Prime Resins is a leading manufacturer of chemical grouts, foams, adhesives and coatings for infrastructure repair and protection. We provide solutions for problems in structural repair, leak sealing, coating/lining, slab lifting, and soil stabilization.

If you are looking for more details, kindly visit Yourun Synthetic Material.

Scope of our business

Our clients range from multinational engineering firms and DOT's to independent contractors. We have customers, dealers, and distributors across North America and around the world.

Prime Resins also provides R&D services special applications for other manufacturers (OEM solutions), and partners on industrial projects sold nationally and internationally.

 Join us October 14-15,  in Conyers, Georgia for our Chemical Grouting Institute.

The Prime Resins Chemical Grouting Institute will teach you the art and science of using chemical grouts for leak sealing, concrete repair, slab lifting and soil stabilization. We go beyond just one application of chemical grouting to give you a whole range of skills to add to your arsenal.

Learn more HERE. 

Understanding the properties of expanding urethane foam is important to optimize performance and success when using the material. They are typically used for part-making, rotocasting, or backfilling purposes. If you’re new to using polyurethane materials, you may not know which properties are most important for your desired application. This comprehensive guide will direct your attention to the essential properties and why you should know what they mean.

What Physical Properties Are Important?

The physical properties of urethane foam refer to the properties of the material when it is in its cured state. As opposed to most other urethane products, urethane foams have few and very different physical properties that matter to the user. They are tested using standard methods from the American Society for Testing and Materials (ASTM) and other in-house lab tests. The following properties are the most important to consider before purchasing urethane foam.

Foam Density / Approx. Poundage

Definition: Foam density is a measurement that indicates the compactness of the foam upon expansion in a given space. In other words, it indicates the weight a cube (12” x 12” x 12”) of foam holds. It is expressed in pounds per cubic foot (PCF). Density can be calculated by dividing the total weight of the foam by the total number of cubic feet. Ex: 100 lb. / 20 cubic feet = 5 PCF.

Importance: Foam density is one of the most critical aspects of choosing the right material for your application. The density selected will depend on the intended use for the foam. The application will also determine if you need a more rigid or flexible foam. There are rigid, semi-flexible, and flexible foams available with similar densities. However, you should only compare densities of like materials (ex. rigid foam to rigid or flexible to flexible).

It is a key indicator of the overall feel and performance of the foam. It determines the durability, strength, and support of the foam as well. Expanding foam densities vary, but common ranges include 3-24 lb. Each will be unique in its characteristics and uses.

The denser the foam, the more compact the material is. Foams at a higher density will typically be more durable and supportive because of their ability to withstand more pressure and compression without losing shape. They will also generally last longer because they are less prone to deformation over time.

Lower-density foams are best for non-structural applications such as taxidermy, lightweight parts, props, and backfilling. They’re typically easier to sand and carve.

Higher-density foams are suitable for similar projects or larger, heavy-duty applications like manufactured and cast stone projects or dunnage because of their durable, load-bearing characteristics. These foams are also more capable of holding objects like nails, screws, and more if needed.

You can also overpack a mold to produce a higher-density foam or a denser skin on the foam. You need to be sure that the mold can withstand the pressure. Overpacking is also a way to save money since you’ll need more dense foam to fill the same space as a less dense foam.

Foam density also directly correlates with expansion rate. The higher the density of the foam, the less the foam expands, and vice versa.

Color

Definition: The color that the material cures to.

Importance: Most urethane expanding foams will be beige/yellow or white, which provides a good base for top coating, if needed. The color doesn’t typically matter to a lot of users due to it being a common backfilling material, so no one will see the material anyway. Painting is recommended if appearance is a concern. For a UV-stable part, we recommend using an in-mold coating that is applied to the mold before the foam is poured or injected.

Some foams can even be formulated to cure to spintoecific colors. They can be pigmented if a solid color is desired for applications such as archery targets. Pigments are added to the polyol (B side) to achieve the desired color before the pot life begins. Too much pigment, however, can affect the cell structure and overall quality of the foam.

Compression at Yield (Rigid Only)

Test Method: ASTM D

Definition: Compression at yield is a measurement that determines the specific amount of stress the foam can withstand under a compressive load before it begins to permanently deform. When compression exceeds the yield point, the material cannot return to its original shape, even after the load is removed. This property is for rigid foams and is expressed in units of pressure like pounds per square inch (psi).

Importance: This property will indicate how well a rigid foam withstands pressure before losing shape. It is not typically relevant for semi-flexible or flexible foams because they are made to compress. Foam with a higher compression at yield will support more weight and handle stress better before it deforms. If you need your foam to be more structural, you’ll typically want to use a high-density foam with a high compression at yield.

Compression at yield is also a factor that determines how firm the foam may be, since it is a measurement of the foam’s ability to resist compression. The higher the compression strength, the harder the foam will be.

What Liquid Properties Are Important?

Liquid properties are the bulk of what foam users want to consider when choosing a urethane foam. These properties apply to the material as a liquid, which are most important when you’re actively working with the material.

Mix ratio

Definition: Mix ratio is a property that tells users of materials with two or more components the exact amount they need of each to produce a solid final product, like urethane foam. The property is expressed as a ratio of the A and B side materials (A:B). Mix ratio can be listed in two ways:

• By weight – The exact proportions of Part A and Part B that must be combined to elicit the correct reaction, measured using an accurate scale. (Ex: VFI- has a mix ratio by weight of 100A:85.12B)
• By volume – The exact proportions of Part A and Part B that must be combined to elicit the correct reaction, measured using mixing containers with volume measurements. (Ex: VFI- has a mix ratio by volume of 1A:1B)

Importance: Accurately measuring the two parts for expanding foam is critical to achieving a proper cure, expansion, and full properties. Not mixing the material correctly can result in a failed or uneven cure. Staying on ratio is important to elicit the best expansion reaction; otherwise, the foam may be brittle, shrink, or not expand fully, making it unusable.

Most urethane expanding foam users choose to measure their material by volume. This is because these foams have simple mix ratios by volume of 1A:1B or 1A:2B, which makes processing convenient and relatively easy. Once measured and added to the same cup, the expansion process will start shortly after mixing. If you don’t stick to the correct mix ratio, you might be at risk of wasting material.

Mixed Viscosity

Test Method: ASTM D

Definition: Mixed viscosity is the combined material’s (A and B side) resistance to flow. It is expressed in centipoise (cps). The chart below lists the viscosity of common household items to help you better compare the mixed viscosity of urethane foam.

Material Viscosity Water 1-5 cps Corn syrup 50-100 cps Maple syrup 150-200 cps Castor oil 250-500 cps Urethane expanding foam 200- cps Honey - cps Molasses - cps Chocolate syrup - cps

Importance: Viscosity is a property that affects the workability of the foam when it is in a liquid state. Foams with a lower viscosity will be much easier to mix, which is essential because of their limited pot life. The easier it is to mix quickly, the better the foaming reaction will be.

Foam with a lower viscosity will also be easier to pour and let flow into a mold. This is nice if you have a complex mold. However, once the foaming reaction starts to occur, the flow of the material will change, and the foam will get thicker. It will also go in the path of least resistance until it is done expanding. This viscosity increase is essential for the foam to reach its final density.

Mixed Liquid Density

Test Method: ASTM D

Definition: Mixed liquid density is a measure of the mass per unit volume of the mixed foam components when it is still a liquid. It is typically expressed in pounds per gallon (lb/gal).

Importance: The liquid density of the foam will not be nearly as important as the density after the foam cures. It can help with calculations to determine how much material you need to fill a specific volume. Most rigid and semi-flexible foams are around 9 lb/gal.

If you determine how much combined material you will be using in weight per gallon and divide that by the mixed liquid density, it will tell you what the starting volume will be. Multiplying the starting volume by the volumetric expansion will tell you the free-rise volume in gallons.

Cream Time (Pot Life)

Definition: Cream time, also called pot life, is the time after combining the two components that you will have before the foam starts to expand. This time frame is usually expressed in seconds to minutes when working at room temperature (77°F).

Importance: Urethane foams are sometimes harder to work with compared to other urethane materials because of their short pot life. It is important to take note of the pot life to successfully use these materials without generating waste. The second the two components touch is when the pot life starts. Some foams only have 30 seconds for you to mix and pour them before the rising process begins. Having everything laid out before mixing the material will make it easier to stay within the cream time.

Consider the size of your project when looking for an expanding foam to use. If you’re working on a large project, you’ll want to make sure you have enough time to mix up the amount of foam you need before the rising reaction occurs.

Several things will impact the pot life, including temperature. If you use the material in really warm working conditions (above room temperature), that will speed up the pot life, which isn’t ideal when the pot life is so short.

Rise Time

Definition: Rise time is the time between the initial foaming reaction and the time at which the foam stops expanding, reaching its highest volume. During this time, the foam will grow and fill whatever cavity or structure it is poured into. This property will usually be expressed in minutes since the foam’s viscosity changes, which causes it to slow down as it rises.

Importance: Rise time is important to know because it will determine how quickly the foam will expand and then begin curing. Having a controlled rise time also allows for proper filling of the mold to prevent defects in the foam, like voids.

A fast rise time may result in an incomplete fill, while a slow rise time gives you more time to work with the material before it fully sets. This makes it nicer for filling more complex-shaped molds. It can also make it easier to sufficiently clamp a mold shut before the foam rises too much. Foams with a longer pot life will also have a longer rise time, handling time, and demold time.

Like pot life, temperature can also affect the rise time. If you’re working in a warmer environment or your mold or material is too warm, your rise time might decrease. If you need the foam to be more pliable for a longer period, you’ll want to work in room temperature conditions or conditions that are slightly cooler.

Tack Free Time (Handling)

Definition: Tack free time, also known as handling time, is the point at which the foam forms an outer skin and loses stickiness. It can be touched and then demolded shortly after. Depending on the foam formula and its pot life and rise time, this property can be expressed in seconds or minutes.

Importance: Tack free time indicates when the foam will no longer be able to pick up dust or debris in the work area. These contaminants are undesirable because they may compromise the appearance and performance of the foam.

Knowing when you can handle the material can be important for certain molding applications, especially when the foam is used as a backfilling material. You’ll be less concerned about when you can remove it from a mold and more concerned about when you can post work and move it. When the foam has lost its tackiness, it will soon be ready for further processing, like sanding, machining, and painting, without compromising the final properties.

Demold Time

Definition: Demold time is the time the material should be left in the mold or form at room temperature (77°F) before it is removed. It is usually expressed in minutes for urethane foams specifically, but other urethane products can take hours.

Importance: All demold times are typically based on a room temperature cure unless otherwise noted. Demold time will vary based on volume, temperature, mold type, and more. It’s important to wait for the foam to cure fully before demolding to prevent deformation. Most foam demold times are pretty fast (same day) for a quick return to service.

If you are making a foam part, you’ll want to know how soon you can remove it from the mold and begin post-work. Shorter demold times are desirable for processing parts quickly. You also want to be careful when demolding so you don’t tear the foam. Most rigid foams should not have a problem, though.

However, demold time is not always an important factor for foam, depending on the application. If the foam is used for backing material, you’re probably less concerned about demolding. In this application, the foam is meant to stick to a thin film of plastic or rubber to make the interior lightweight with a durable outer shell.

Cure Time

Definition: Cure time is the amount of time it takes for the foam to reach its full physical properties. Most cure times are listed as hours.
Importance: On initial cure or when you are able to handle the foam, it will not have developed full properties. Once the foam has cured, it will perform as per the properties listed on the technical data sheet. The cure time can be affected by many factors, with temperature being the most common.

Approximate Volumetric Expansion

Definition: The approximate volumetric expansion of a foam determines how much it will expand by its original liquid volume once fully risen.
Importance: Foams that are lighter in density will typically fill more volume and expand at faster rates. For example, a 3 PCF foam like VFI- will expand nearly 23 times its original liquid volume, while a 20 PCF foam like VFI- will rise under 4 times that.

The expansion rate can be affected by multiple factors, including temperature, mixing technique, humidity, and mold shape. Higher temperatures and humidity will increase the reaction. If you rapidly mix the material, you may also see a greater foaming reaction. However, if your mold is thin and tall, you may see less reaction.

Where to Find Material Properties?

VFI urethane foam properties can be found on all product pages and technical data sheets. Navigate to the product page of any foam product, and you will be able to find physical and liquid properties listed on the right-hand side of the page or the TDS listed under resources. For mobile users, these tabs are at the bottom of the product page. The VFI- Series has a special family sheet, which lists all our rigid foams and their properties in one place.

We pride ourselves on providing accurate properties for all our products, so various test methods are used to determine these properties before they are posted.

Contact VFI if you need further assistance finding foam properties or determining a foam that’s perfect for your project.

Because urethane plastics tend to have high surface energy, most can be primed and painted, providing part makers with a range of color options to improve aesthetics, create a production quality finish, or blend with other parts. If you’re having issues painting your industrial, rotocast, or prototype part, there may be something on the surface preventing the paint from adhering properly. Alternatively, the paint or primer you’re using may be incompatible with the plastic.

Most VFI urethane plastic products are neutral or white after cure and are made to be fully paintable. Make sure to read the technical data sheet for the specific product you are using to ensure you are creating a good surface that will accept paint.

Reasons Urethane Won’t Accept Paint

1. Poor Surface Preparation

The biggest reason paint fails to adhere to a urethane plastic part is due to poor preparation of the surface. Issues will typically arise most in indentations, creases, or other hard-to-reach areas. Poor surface preparation can mean that you have failed to do the following:

     a. Clean the Part

As with any coating application, it’s essential for the surface to be clean for proper adhesion. After demolding and allowing the new parts to sit, they may attract dirt, debris, or oils from being touched. Leaving these contaminants can disrupt the adhesion of the paint you’re trying to apply.

Another contaminant is mold release. The majority of urethane parts are cast into metal or silicone tooling. While release is not required for silicone molds, it may still be used to ensure longevity of the tooling due to the wear and tear that urethane can cause. For metal or urethane prototyping molds, release is necessary; otherwise, the materials will bond together. If any release residue is still on the plastic part when you try to paint it, you’ll have issues getting it to stick. The paint may even bead up on the surface. And some release agents are hard to remove, so you need to be cautious.

     b. Prime the Part

Urethane surfaces typically turn out glossy, smooth, and non-porous, so it’s hard for paint to grip onto. Not preparing the surface with primer can prevent the part from accepting the paint. Even if a primer is not always necessary, sometimes it’s recommended to ensure that a bonding layer is created for the successful painting of parts.

     c. Sand the Part

The surface of the urethane after cure will not be acceptable for painting if it hasn’t been primed. Alternatively, if the surface is not abraded in some way, the paint might not be able to grip onto the surface. The shinier and smoother it is, the harder it will be for the paint to adhere long-term to the part.

2. Poor Mixing / Mix Ratio

If your urethane part feels oily or sticky after it has cured, this can be a problem when applying paint. The paint might not dry or may come off the part easily. It’s likely that either the material wasn’t mixed thoroughly enough, which resulted in uncured material throughout the part, OR the wrong mix ratio was measured, which resulted in too much of one material (typically the B side, Poly) being used. Mistakes during this part of the casting process are usually due to rushing when using plastics with limited pot lives.

3. Incompatible Paint

Not all paints are compatible with urethane plastic. While urethane adheres to almost anything in its liquid state, it doesn’t have the same properties once cured. Based on the properties of the paint and the urethane, some generic paints might crack, peel, or scratch off the part easily. If you use a highly rigid or DTM (direct to metal) paint, it might not have enough flexibility to be compatible with the urethane part.

Solutions

When mixing the material, make sure you use the proper ratio by weight or volume to ensure you end up with a fully cured part. Also, make sure you are mixing thoroughly to prevent streaks of unmixed material that may affect the surface of your part. If you need a longer working time, find a material that accommodates this, so you can manufacture quality parts. Allow the part to cure for several days before painting.

Wash your part to get rid of any release residue, dust, grease, and other contaminants. Typically, a mild detergent and water are recommended. Some part makers have seen success by wiping it down with isopropyl alcohol. Also, some release agents won’t make it as difficult to paint your urethane part, so consider finding one that won’t interfere with painting.

If you want to avoid using release altogether so you don’t have to worry about another post-processing step, use platinum silicone tooling over metal or urethane.

Apply a primer specifically made for plastics, like an automotive primer. In some cases, rather than priming the casting after demolding, some part manufacturers put a light coat of primer on their tooling surface after a release agent is applied. The primer will bond to the urethane plastic and should come out of the mold ready to paint. Allow the primer to dry for the time recommended by the manufacturer to get the best bond.

If you don’t want to use a primer and don’t need a smooth finish, sanding the surface will be your next best option. Lightly scuffing the surface with fine-grit sandpaper or sandblasting will create a rough surface for the paint to adhere.

You want to find a paint that will provide high adhesion to the part. Several acrylic and autobody paints have been proven to work well for these parts. Individual testing for paint compatibility may be necessary. When applying the paint, apply multiple thin coats as specified by the manufacturer to avoid excessive drying, warping, or poor adhesion between layers.

If you don’t want to worry about painting your part, find a pigmentable plastic that you can tint to your desired color. If necessary, ensure the plastic has UV stability to prevent color shifting from occurring.

Paintable VFI Plastics

• VFI-110 75 D Injectable Plastic is fully paintable when primed.
• VFI- 80 D Injectable Plastic is fully paintable when primed or sanded.
• VFI- 70 D Fast Casting Plastic, VFI- 70 D Casting Plastic, and VFI- 75 D Slow Casting Plastic provide a neutral color that can be primed or sanded, then painted after full cure.
• VFI- Polyurethane Casting Plastic Series (VFI-, 81, 82, 85, 86) are neutral for easy priming before top coat application.
• VFI- 85 D Prototyping Polyurethane Plastic flashes white and is paintable after post-cure.

Contact VFI if you need help finding the best paintable urethane plastic for your project.

VFI offers several products to accommodate the application of spray-on truck bedliner. The two methods most utilized are Qwik Spray and high-pressure. These types of spray equipment are vastly different from each other, so do you know which is best for your autobody shop?

Cartridges are an inexpensive way to enter the bedliner industry, especially if you’re only planning on spraying at lower volumes or providing patch repairs.

High pressure bedliner is better for autobody shops spraying consistently at mid to high volumes. This is more so due to the upkeep associated with the equipment.

Regardless of the method, bedliner application helps protect truck beds from scratches, rust, and wear caused by hauling tools, materials, and heavy cargo—extending the life of the vehicle and boosting resale value.

While the technical side of spray equipment matters, so does having access to a trusted platform for parts, tools, and solutions tailored to vehicle professionals. Blue Wrench has emerged as a resource for mechanics and autobody technicians seeking dependable automotive repair products, streamlining everything from diagnostics to refinishing tasks.

In that context, bedliner application isn’t just a one-off service—it becomes part of a comprehensive approach to vehicle care. Whether a truck is in for collision repair, custom work, or routine maintenance, applying a durable bedliner demonstrates a commitment to long-term protection and client satisfaction.

Integrating it into your workflow ensures your shop stays competitive while delivering practical value to every customer.

VFI has put together this guide to help bedliner applicators weigh the pros and cons of these polyurea hybrid products and the associated spray equipment.

Note: You will need a designated spray booth for proper ventilation. Always wear personal protective equipment, such as an approved respirator, when spraying.

Qwik Spray Gun & Requirements

The recommended applicator for this spray method is the VFI- Qwik Spray Gun with GS-15 Static Mix Tips. Cartridge-based equipment like this utilizes air to atomize the material. Air compressor requirements to run the Qwik Spray Gun are dry air capable of supplying 10 cubic feet per minute (CFM) at 100 pounds per square inch (PSI) minimum.

The trigger on the Qwik Spray Gun uses a continuous flow and should not be stopped once pressed. If you stop, the material will cure in the static mix tip, and you’ll have to swap tips before restarting.

VFI’s cartridge-based bedliner is VFI-544 Qwik Spray Bedliner.

High Pressure Spray Rigs & Requirements

Recommended rigs for this spray method are plural component Graco air, electric, or hydraulic sprayers that can accommodate temperature and pressure recommendations. High pressure rigs utilize heat and pressure to produce a fine, even texture. The equipment should be able to provide a minimum of 2,000 psi of constant pressure at 150-155°F.

High pressure guns have a controlled trigger, which can be released during application. You do not need to spray constantly, as the material mixes right before it leaves the spray gun.

VFI’s high pressure bedliner is VFI-542 High Pressure Spray Bedliner.

Qwik Spray vs High Pressure Material Properties

Properties High Pressure (VFI-542) Qwik Spray (VFI-544) Hardness Shore D 57 D 40 D Tensile Strength 2,410 psi 2,182 psi Elongation 80% 110% Tear Strength 241 pli 187 pli Yield Strength 12,987 psi 551 psi Gel Time 4 seconds 4 seconds Tack Free 28 seconds 28 seconds Recoat Time 2 hours 4 hours

Cartridge-Based Spraying Advantages

1. Portable

As long as you have an adequate air compressor and the lightweight applicator, you should be able to take your bedliner on the go if you don’t plan to only spray at your shop. High-pressure equipment is heavy, and most rigs can’t be transported easily, so cartridges are a great alternative. Note: Portability will also depend on the size of your air compressor.

2. Cost-Effective for Limited Spraying

If you’re looking to have bedliner application as an additional service to your autobody shop, you’ll probably be more interested in Qwik Spray equipment. It’s a great addition to your offerings if you’ll only be spraying a few truck beds per month.

The initial startup costs of the Qwik Spray Gun are much lower than if you were to work with a high-pressure rig. While the material might cost more, you won’t have to justify the equipment costs if you’re not spraying consistently. Typically, a single case (6 cartridges) covers an entire truck bed.

This spray method also reduces labor costs because there’s less setup and cleanup. With the two components already pre-measured in the cartridges, you don’t have to worry about pre-mixing materials, checking for correct mix ratios, etc. All you need to do is make sure the rest of the truck is taped up and covered to protect it from overspray.

If your spray load increases substantially, you may then consider upgrading to high pressure equipment to save on material costs. A cartridge kit is just under a gallon of material and is more expensive than purchasing gallons or drums.

3. Limited Training Needed

Before cartridge-based bedliners were created, you had to have specialized training and knowledge to use high pressure machines effectively. Now, the material is more accessible with this user-friendly application method.

VFI’s Qwik Spray applicator is easy to use from start to finish, with minimal training necessary. We even offer a guide with pictures on how to use the Qwik Spray System. With a built-in airflow regulator, you’re also able to easily adjust the flow and pattern you desire while spraying.

Note: New bedliner applicators will need to practice to achieve a consistent, textured finish.

4. Reduced Equipment Maintenance & Easier Cleanup

With the Qwik Spray applicator, you have few replacement parts to worry about if the gun breaks down. It has no hoses, fittings, pumps, or other expensive machine parts like a high-pressure system has.

Disposable cartridges and static mix tips also make cleanup much easier. You don’t have to worry about flushing spray lines with solvents or doing regular maintenance on your rig to prevent downtime. If you’re not constantly spraying or cleaning the machine enough, old material can clog up the lines as well.

5. Improved Non-Slip Protection

The VFI-544 Qwik Spray Bedliner is a bit softer than its high-pressure counterpart, which gives it a bit more grip. Because cartridge-based bedliners spray at a lower pressure, a less fine texture is produced, which creates a better skid- and slip-resistant surface. If you need the bedliner to have these features, the Qwik Spray Gun might be a better option.

High Pressure Spraying Advantages

1. Best for High Project Volume

If your autobody shop has enough business where you’ll be spraying truck beds consistently, high pressure is more cost-effective in the long run. It has a higher initial investment due to equipment costs, but high-volume spraying should help you make that back quickly. Drums and tote prices are typically more affordable due to the way the material is packaged vs cartridges.

High pressure equipment also has to be used regularly for maintenance purposes. If you’re spraying almost every day or a few times a week, you shouldn’t have to worry. If you do not have plans to use your high-pressure rig for an extended period, make sure to flush the lines to prevent bedliner buildup.

2. Allows for Versatile Material Options & Applications

Premium bedliner options like polyurea coatings are available for high pressure spray equipment. The VFI-200, VFI-201, or VFI-202 50 D Polyurea Coatings are recommended if you want a higher-end bedliner. However, polyurea hybrid coatings work just as well and can be sprayed in a high pressure and cartridge format.

You’re also not limited to spraying truck beds. If you need to make the cost of the equipment worth your while, you can spray different parts of the vehicle or other recreational vehicles like ATVs, boats, side-by-sides, and even utility trailers, ramps, work trucks, etc. We’ve also provided these products to users with vastly different applications like tank pads, table edging, and speaker boxes.

3. Better Control When Spraying

Because you don’t need to constantly hold onto the trigger while spraying, you can control how and where you spray. This makes it easier to get a consistent thickness across the board, as well as a desirable, uniform texture for the final finish.

High-pressure creates a very fine texture, which is much nicer than some low-pressure options. Because cartridge-based coatings utilize lower pressure and no heat, they produce a less fine texture. If texture matters, this may be something to consider when choosing equipment and materials.

You’ll also save material with high pressure because you can stop at any time once you’ve completely coated the truck bed and reached a desirable thickness. The spray equipment only mixes what you need, so you can store leftover material with a nitrogen purge once you’re finished. Most truck beds utilize 2-3 gallons of material, depending on the size of the truck.

4. Higher durability

Because the VFI-542 High Pressure Bedliner has higher tensile and tear strength as well as higher hardness, it is more resistant to physical damage, wear, and tear. This makes it durable and reduces the amount of chips, scratches, and dents over time. It is also less susceptible to the effects of temperature changes.

5. Good for On-Site Spraying

For the most part, bedliner is typically sprayed in a consistent location. There’s not usually a reason to go somewhere else to spray unless that’s a service you would like to offer. So, if portability isn’t desirable to you, look into a high pressure rig.

Regardless of the equipment you choose, both coatings provide similar, durable protection for truck beds.

Contact VFI if you need further assistance choosing the right bedliner and equipment. We also have a separate low-pressure version, primer, and UV-stable top coat to round out your line.

In the part making and prototyping world, understanding the properties of urethane plastic is essential for choosing the best material for a specific application. If you’re new to using thermoset polymers like urethane, you may not know which properties are most important for making plastic parts. The answer will vary based on how you need your parts to perform. This comprehensive guide will lead you through all the essential properties and why you should know them.

What Physical Properties Are Important?

The physical properties of urethane pertain to the material when it is in a cured state. These properties will tell a urethane user how their cast parts will hold up in their desired application. They are tested by manufacturers and third-party laboratories using standard methods from the American Society for Testing and Materials (ASTM). The following are the most popular properties that manufacturers list on their technical data sheets:

Shore Hardness

Test method: ASTM D

Definition: Shore hardness indicates a material’s resistance to indentation or deformation. Materials are compared using different scales based on similar characteristics. The higher the number on the scale, the greater the plastic can resist indentation, meaning the part is increasingly harder.

Importance: Shore hardness is a factor that indicates the durability, flexibility, and machinability of urethane plastic. High performance plastics are measured on the D scale from medium hard to extra hard (20 D – 90 D).

A rigid material is typically more durable, abrasion-resistant, and can bear more weight than softer, flexible materials. Many high performance plastics are rated 60 D and above, indicating that they are very tough and resistant to tears with limited flexibility, if any.

These hard plastics are a great choice for making parts that will experience a lot of wear and tear, such as production parts and equipment housings. They are highly suitable for applications where rigidity, wear resistance, and dimensional stability after cure are crucial.

Note: When looking at VFI urethane plastics, you will notice that they all include the Shore hardness in their names to make it easier to find what you’re looking for (i.e., VFI- 70 D Fast Casting Plastic).

Tensile Strength

Test method: ASTM D638

Definition: Tensile strength is the maximum load a material can support before it breaks or fractures when stretched. It has also been called a tension or pull test and is expressed in pounds per square inch (psi).

Importance: Parts are often subjected to various types of stress (tension, compression, bending, etc.), so tensile strength is important for determining if a urethane part has the structural integrity and durability to resist tension forces. The ability to sustain higher stress than other materials is one of polyurethane ’s greatest qualities.

A part with high tensile strength can withstand significant loads without breaking. Applications where the material will be subjected to constant stress, such as industrial parts, rotocast parts, and tooling, can benefit from high tensile strength. These parts are less likely to fail, so you can count on them to perform in tough situations. Materials with higher tensile strength also tend to be rated higher on the shore hardness scale.

Tensile Modulus

Test method: ASTM D638

Definition: Tensile modulus is closely associated with tensile strength as it relates to the ratio of tensile stress to strain when a material undergoes deformation when stretched. It is a calculated number that uses the same test method and measurement (psi) as tensile strength since both test tension (pulling) force.

Importance: Tensile modulus is a property that helps you determine how stiff or rigid a urethane plastic part will be under tension. It will also tell how much the part will deform or elongate under that force. A high tensile modulus is great for applications that require high stiffness and minimal deformation to increase the longevity of the part.

When a part has a high tensile modulus, it means it will resist stretching. It has great dimensional stability to maintain its shape under consistent loads. Like tensile strength, it is often associated with hardness. Harder parts may have a higher tensile modulus, though some custom formulas can break this standard.

Flexural Strength

Test method: ASTM D790

Definition: Flexural strength measures the maximum force needed to bend a material until it breaks. Like tensile strength and modulus, it is expressed in pounds per square inch (psi).

Importance: Many applications subject plastic parts to bending forces in everyday use. A part with good flexural strength can handle this stress without snapping, breaking, or warping. Knowing flexural strength will make it much easier to identify if a material is strong enough to resist deformation. High flexural strength parts are durable and will keep their shape and function better for longer. If a material’s flexural strength is on the lower end of the spectrum, it might mean that the material is more brittle. Plastics with higher flexural strength will usually be rated higher on the hardness scale, which helps them resist the bending force.

Flexural Modulus

Test method: ASTM D790

Definition: Flexural modulus measures a material’s stiffness or resistance to a bending action. It uses the same test as flexural strength and is expressed the same (psi). It is different from tensile modulus because it tests a material’s resistance to deformation when bent, whereas tensile modulus tests this resistance when stretched. Both properties, however, indicate a material’s rigidity.

Importance: Flexural modulus is important because many part makers require a certain degree of stiffness in their plastic parts to withstand bending forces. A higher modulus means the material is stiffer and will bend less under a specific load. Understanding this property and how it affects the performance of plastic parts makes it easier to create quality components for high-stress situations.
Parts with a high flexural modulus are also strong and rigid, so they can provide support where needed. Rigid parts are used for applications like automotive parts, gears, furniture pieces, etc.

Shrinkage Linear

Test method: ASTM D

Definition: Linear Shrinkage is the change in the length of a material along linear dimensions (length, width, and height) as it cures. The contraction is usually expressed as inches per inch (in/in) and tests a 12 x ½ x ½ sample.

Importance: Part makers should know that urethane plastic shrinks as it cures, which could affect a part’s final dimensions. Most shrinkage will occur when the part is cooling in the mold, and a small amount can occur after demolding.

The rate of shrinkage is dependent on several factors. Some plastic materials might not have thermal properties to withstand shrinkage. Processing conditions like temperature, pressure, and flow rate can increase the shrinkage of a part as it cures. The part size, if you are using a lot of material to make large parts, can also cause shrinkage.

When you know how to work around linear shrinkage, you can maintain consistent part dimensions throughout production runs. If a part is undersized, it might not be able to perform its intended function, which can be a waste of time and materials.

Izod Impact

Test method: ASTM D256

Definition: Izod impact is a test method that measures a material’s toughness or resistance to impact. It is used in the polymer manufacturing industry to determine the toughness of plastics. It is typically measured as the amount of work required (ft-lb) to break the material a certain amount (in). The two ways Izod is tested are:

• Notched: It tests impact resistance from a swinging pendulum with energy focused on a notch. This measures the material’s ability to absorb impact despite having a flaw (the notch). Calculated values are typically lower because a notch is much easier to continue breaking and simulates real-world situations better.
• Unnotched: It tests impact resistance from a swinging pendulum with energy focused on the entire test piece so force is distributed more evenly. There is no premade notch because it measures the material’s overall toughness. Calculated values are typically higher and might not represent real-world situations where imperfections are likely.

Importance: Good impact resistance is essential for plastic parts that might experience sudden force, shock, or blows. It allows part makers to determine which materials will have the necessary toughness needed to create durable, long-lasting parts. Understanding impact resistance can also help prolong the life of your part and prevent it from failing in high-impact scenarios.

A material’s impact resistance can vary based on the type of material, how thick it is, and external conditions. Urethane plastic can be customized with different properties and has the benefit of being as soft or hard as you want it to be. Softer urethane plastics are going to be better for impact resistance.

However, Izod impact is just one property that can tell a user how tough a material is. Other factors that affect the strength of a material include tensile and flexural strength, which may be more important depending on the application.

Heat Deflection Temperature

Test method: ASTM D648-18

Definition: Heat deflection temperature (HDT), also called heat distortion temperature, is a thermal property unique to polymers and plastics. It tests the maximum temperature at which a material deforms under a given load. Depending on the material, it will be tested at 66 psi or 264 psi.

Importance: HDT determines if a plastic part can remain rigid and keep its shape under high temperatures and constant loads. When a part reaches its HDT for an extended time, it will lose its load-bearing capability and may fail. This is why you must look at the HDT if you know you’re making a part that will be exposed to elevated temperatures.

A material’s HDT can be affected by several factors. The longer the material is exposed to heat, the more likely it will deform. If the direct or indirect temperature rises slowly, the material might have a higher HDT. The size and shape of the part can also change the HDT, as the thicker the part, the higher the heat transfer rate.

When urethane plastic has a high HDT, it’s better at retaining its shape and functionality in high-heat applications. Some industries where HDT would be important include packaging components, automotive parts, electronic pieces, and medical devices.

Note: VFI also has plastics with fire-retardant in their formula for part-making in a variety of industries, such as medical, automotive, and aerospace.

Cured Color

Definition: Cured color is the color that a material cures to.

Importance: Cured color can affect your plans when making a urethane plastic part, as it is not the same for every product. Some products have a manufacturer’s standard color, but most come neutral, white, or even UV-stable clear to make them customizable to the user. Neutral-colored plastics allow part makers to paint the cured surface for a production-quality finish. However, painting can be avoided by using dyes and pigments to alter the color. Pigments are added to the polyol (B side) before mixing for more time to achieve the desired color before the pot life begins.

However, cured color may not always be important for an application. If your part is hidden from sight or used as an internal component, you probably don’t need to be concerned about this property or UV stability. Most plastic materials on the market are aromatic, and that is okay for most users. If you need a UV-stable part, you should look for products marketed as UV-stable.

What Liquid Properties Are Important?

While not all companies separate physical properties from liquid properties, VFI does, so you can identify which applies to a material when it’s a liquid and when it’s a solid. The following properties are important to know when working with liquid urethane plastic:

Mix Ratio

Definition: Mix ratio is a property that establishes the exact amount of material to combine to produce a solid final product, such as urethane plastic. This property is reported as a ratio for materials with two or more liquid components that must be mixed together. A mix ratio can be expressed in two ways:

• By volume: Using equal-sized containers or dispensing equipment to measure the exact proportions of two or more components that must be combined. It is not dependent on weight.
• By weight: Using an accurate scale to measure the exact proportions of two or more components that must be combined. It is not dependent on the volume.

Importance: Following the mix ratio of any urethane plastic is crucial because it directly affects the chemical reaction that allows the plastic to cure. The combination of materials will ensure that the plastic will develop strong cross-links that lead to a durable, high-strength part.

If these materials are mixed incorrectly, it can result in an incomplete cure. The plastic might be weak, soft, or sticky and won’t function as needed. In some cases, it may never develop full physical properties. Use the proper mix ratio to be sure your parts produce consistent results from batch to batch and reduce material waste.

Viscosity

Definition: Viscosity is a measure of a fluid’s resistance to flow at room temperature (77°F). Many manufacturers list several viscosities for their materials if they include more than one component (i.e., A side, B side, and mixed). It is expressed in centipoise (cps). For a better understanding of the viscosity of urethane plastic, here is how it typically compares to some household items:

Material Viscosity Water 1-5 cps Corn syrup 50-100 cps Maple syrup 150-200 cps Castor oil 250-500 cps Urethane plastic 80- cps Honey - cps Molasses - cps Chocolate syrup - cps

Importance: Viscosity is an important property that impacts how you work with a material and affects some of the cured material’s final characteristics. It helps determine how easy it is to pour the urethane into a mold. A low-viscosity material will have a better time flowing into intricate molds with tight corners for detail reproduction.

Low viscosity urethanes are also less likely to trap air bubbles while curing. As the material flows into a mold, the bubbles dissipate more easily to minimize voids and imperfections in the cured plastic. Not only does the surface finish look better, but fewer voids help the material exhibit better performance characteristics.

For quality assurance, you can vacuum degas and pressure pot materials to reduce air entrapment further. These techniques are essential if you are making clear plastic parts.

Pot Life/Work Time

Definition: Pot life or work time is the time it takes for a material’s viscosity to thicken to a state where it is deemed unworkable. More simply, it is the amount of time you can work with the material before it becomes too thick and begins to cure. This can be expressed in minutes or hours, depending on how fast the material sets at room temperature (77°F).

Importance: Since urethanes are customizable, the pot life can be varied depending on a user’s processing needs. There are unique plastic materials that are extremely fast and can only be worked with for 2 minutes, and there are some materials that have a working time of 2 hours or more.

Pot life can always be affected by the temperature of your material, environment, and mold. If you are working above room temperature, your pot life is guaranteed to decrease, which means you’ll have even less time to work with the material. However, some people are okay with increasing the temperature as this can also decrease the time it takes for the part to be ready to demold.

Depending on how big of a part you are making, make sure the material you choose provides enough time to mix, degas, and pour the material. For a material that has an extremely fast pot life, a different casting method is recommended. You will typically not have enough time to mix and pour the liquid before it sets, so injection molding is the processing method that would utilize fast resins.

Gel time

Definition: Gel time is the time it takes a material to stop flowing or become gel-like. It is typically measured in minutes or hours, as it comes shortly after the pot life ends. Like pot life, it is assessed at room temperature (77°F).

Importance: While gel time might not be as important as pot life, it can help you plan your project so you know your workable window. It will also help you avoid mistakes caused by exceeding the workable timeframe and prevent you from wasting material.

Demold time

Definition: Demold time is the time a casting should be allowed to cure before removing it from a mold. It is usually expressed in minutes or hours, depending on factors like pot life and gel time.

Importance: Your material’s demold time is important for part production. Like pot life, demold time can vary depending on the formula. If you are processing parts that must be ready quickly, you’ll want to find a material with a short demold time. If you need to pour large parts, you’ll need a material with a longer working time, but this will result in a longer demold time.

Something to note about demold time is even if your part is ready to be demolded, it will not have full physical properties. Some plastics are unique and require post-curing in an oven to achieve full physical properties. Heat can help any material obtain its properties faster; otherwise, your parts will take a few extra days to obtain the properties listed on a technical data sheet.

Where to Find Material Properties?

It is very important that material properties are correctly listed so that users can trust the material will perform as expected. Our on-site lab uses various standard ASTM test methods to determine the unique properties of each material. Once they have been reviewed thoroughly, we post them on all our product pages and the technical data sheet for each product. Technical data sheets can be found on any product page under resources.

So, you’ve done everything right in the process of making your mold, but after you’ve demolded it, it’s begun to deform. We’ve seen this happen to urethane rubber users periodically, and there can be several reasons this defect occurs. The biggest reason is time. You’re either demolding your mold or casting into it too quickly.

How you make the mold, use it, and store it can also affect its ability to hold shape over time. Once a mold becomes deformed, its usability is greatly reduced. This leads to a shortened lifespan, which increases production costs and downtime from having to remake the mold. The best way to maintain your mold is by reading the technical data sheet (TDS) and adhering to the instructions and guidelines listed by the manufacturer.

Reasons Your Mold is Deforming

1. Demolding Too Early

Many factors affect how fast your mold cures, including temperature, mold wall thickness, mold size, etc. If you don’t adhere to the recommended guidelines when making your mold, the pot life and demold time can change. If you lose track of them, you may run into issues.

If you demold too soon, the rubber might not have hardened enough to maintain its shape, causing it to warp or deform when you remove it from the mold box. Early removal can also cause damage because it is soft and prone to tearing. Even if the mold seems cured on the surface, it probably hasn’t cured internally.

At this point, since the mold is distorted, your future casting probably won’t be an accurate representation of the original object. If you want to demold it faster, you’ll have to use a faster material.

2. Casting Too Soon After Demolding

Many newer polyurethane users think that once the mold can be demolded, it’s ready to use. However, if you use it right after you pull it out of the mold box or form, you can deform or distort it.

Urethane initially cures after 16 hours and can be demolded, but it still needs to develop the necessary strength for various casting scenarios. Most manufacturers will recommend an additional waiting period after demolding before you use the mold. For products with demold time of 16 hours it is recommended to wait 72 hours.

Note: The longer you wait to cast into your newly made mold, the stronger it will be. Urethane develops full physical properties after 7 days. If you don’t want to wait, heating the mold can typically increase its physical properties faster.

3. Not Storing the Mold Properly

If you aren’t casting into your mold for a length of time, you’ll probably want to store it for later use. Do not store it vertically or on its side. Urethane can distort if it’s not stored on a flat surface. If a corner is curled, the mold is on top of another object, or something is lying on top of it, it may never go back to its original shape.

Also, don’t store it outside or in direct sunlight. Elevated temperatures and UV rays can negatively affect the mold. This may prevent you from getting accurate castings the next time you use it because the mold may have shrunk, expanded, or degraded.

4. Using the Mold in Extreme Temperatures

The type of deformation extreme temperatures cause will not ruin your mold, but it will change its shape. These extreme temperatures cause the mold to change because the rubber will expand and contract with the weather.

In most cases, this change might only be temporary. If the mold has expanded, it’s probably due to high temperatures, but if it has shrunk, it’s probably due to low temperatures. Dimensional changes often occur because you are not using the mold in the same conditions that you made it.

If you are constantly working in extreme temperatures, your mold may never return to its original size. This results in your castings being an inaccurate representation of the original model(s).

Note: Some solvent and oil-based release agents can also cause your urethane mold to expand. Unlike temperature, this will deform the mold permanently and cannot be reversed.

5. Mold Design Does Not Accommodate the Casting Material

Before you even begin to make your mold, you need to consider the design, what materials you are using to make it, and what materials you will be casting into it.

The thickness of your mold walls plays a big part in preventing your mold from distorting. We know you want to save money on material costs, but if you don’t make your walls thick enough, they may bulge in the casting process. Molds with complex shapes are prone to warping as well.

If you’re making a mold with thin walls, you must be sure it will hold up to the material you’re casting into it. Materials like concrete are heavy, and if your mold isn’t strong enough, it will distort during the casting process.

The hardness of the mold can also determine how it might deform if not designed well. If you use a softer rubber (25-45 A), you cannot pour the walls thinner than ¾ – 1 inch thick. Otherwise, it might not accommodate the weight of the casting material, especially if you are casting something big.

Also, thinner areas of the mold can take longer to cure. You might think you’ve given your mold enough time before casting, but it takes a little longer for thinner parts to gain the strength necessary to do so.

Solutions

Take your time, and don’t rush when demolding your newly made mold or casting into it. Check the manufacturer’s TDS to be sure you are following recommended cure times and temperatures.

When making the mold and casting, do so at room temperature (77°F) for the best results. All VFI products are tested with properties obtained at room temperature. Anything outside of that temperature will change the pot life, demold time, and dimensional stability of the rubber.

VFI recommends leaving your demolded urethane mold on a level surface at room temperature (77°F) for an extra 3 days. This will maximize the performance of the mold and allow it to gain enough properties for casting. You’ll be able to repeatedly cast into it without worrying about distortion.

A good rule of thumb is to use a harder rubber when making large castings. This way you can make the mold walls thinner because the rubber will have more tear resistance and can support heavier loads. On the other hand, if you use a softer material, make the mold with thicker walls to help cure it quicker and to give it additional structural support.

Urethane will cure quicker in thicker areas. Be sure you’re following the thickness requirements recommended by the manufacturer to withstand the pressure of casting materials. VFI’s recommended wall thicknesses are listed on every TDS. If you’re pouring under what’s recommended, you’ll need a rubber with a higher Shore hardness.

Since urethane rubber is meant to be reusable, you want to do everything you can to keep using it. The best way to extend the life of your mold is with proper care and storage. That means when you’re not using the mold, you want to store it flat, in a dry, temperature-controlled location, away from direct sunlight.

Do not stack urethane molds on top of or underneath other molds. They might stick to each other, which will require force to tear them apart and weaken the rubber. If you store them in contact with molds made of different materials, this can cause swelling, shrinking, and distortion from the transferring of oils or plasticizers.

Contact VFI if you are still having problems with your urethane mold distorting or if you have other technical issues.

Before making a mold, the most important thing to consider is how much liquid rubber you’ll need. Several factors will affect the amount, including the complexity, depth, width, and length of your model(s). Also, consider how thick you want to make your mold to ensure longevity and reusability.

If you use too much rubber, you’ll end up wasting material, but if you use too little, you may run out during the mold-making process and have to scramble to mix up more.

Before you can begin estimating, the first step is making a mold box or form. You must determine how far apart to place your models if you’re molding over multiple objects and the overall mold wall thickness. Then, you’ll have a better understanding of the empty cavities that need filling.

Why Mold Thickness Matters

Mold wall thickness is a critical element in the design of your urethane mold. It considers the thickness of the sides and bottom of the mold. How thick you should pour the rubber is determined by if the mold is going to be supported in a mold box and the number of incuts and intricate details that are present.

All VFI molding rubbers have a minimum pour depth that can be found on our TDI specification sheet or the individual technical data sheet (TDS) for each product. Follow these specifications to have the necessary tear strength of flexibility for proper demold and use of the mold.

Lower durometer rubbers (20-60 A) are softer and more flexible, which is why they must be poured thicker. If they are poured too thin, they can be weak and prone to tearing. They are recommended to be poured ¾ of an inch to 1 inch thick. Molds made of these rubbers are typically used for cast stone and manufactured stone projects.

A thicker mold will prevent the mold from deforming during the casting process and increase tear resistance. Thinner walls might make a flexible mold bulge from the pressure of the casting material. The castings created will not be exact replicas of the original. To prevent this, you would need to build a mold box to keep the mold from deforming.

As the rubber’s durometer increases, the minimum pour thickness decreases. The material is less flexible but will have good tear strength. These higher durometer rubbers (70-90 A) are typically best for larger precast concrete projects like formliners, stamps, or rollers.

Thinner pours (between 3/8 of an inch to ½ an inch) use less material, which also keeps material costs lower. They can be very large, which is why mold makers want them to be as light as possible for easier handling during the casting process.

Note: Thinner pours of urethane can take longer to cure. When less material is used in certain areas, it creates a smaller exothermic reaction. The less heat generated, the slower the material will cure.

Also, as a rule of thumb, we generally recommend pouring at least half of an inch above the tallest point on your master. This will create a thick enough mold bottom that withstands the abrasive effects and weight of materials like concrete.

How To Calculate Mold Size

Once you’ve determined how thick you need to make your mold walls, you can assemble your mold box and find out how much material you need to fill it.

There are a few calculations used to determine how much material you need. First, you need to find the volume of the mold box in cubic inches. Most molds are square or rectangular in shape, so we use the simple math formula length x width x height to determine the volume.

• Formula: L x W x H = volume (cubic inches)

Ex.) Box dimensions: 11 ½ inches x 5 ¾ inches x 2 inches = 132.25 cubic inches (in3)

Once you find your mold box volume, you also have a model(s) inside that will take up space. This will reduce the amount of material you need to fill the space. You can calculate the volume of your model(s) using the same formula.

Ex.) Stone dimensions: 9 ½ inches x 3 ¾ inches x 1 inch = 35.625 in3

If you’re using multiple models, you’ll need to determine the volume of each. You can then add each model volume together to get an overall total model volume.

Once you have both volumes for your mold box and model(s), you’ll need to subtract them from each other to figure out how much of the space needs to be filled.

• Formula: Box volume (cubic inches) – model volume (cubic inches) = total volume of material needed (cubic inches)

Ex.) 132.25 in3 – 35.625 in3 = 96.625 in3

The next thing you’ll need to do is convert your volume into a weight measurement, like pounds (lb). The information you’ll need to do this is specific volume. VFI provides this property for all our products under liquid properties on each product page and technical data sheet. We typically recommend using 26 in3/lb. because it will accommodate some extra material in the event that waste occurs.

You’ll need to divide the cubic volume by the specific volume to determine the total weight of material needed, which means the combination of both A and B side materials.

• Formula: cubic volume ÷ specific volume = weight (pounds)

Ex.) 96.625 in3 ÷ 26 in3 = 3.7 lb. (Part A + Part B)

We would then round that number to a whole number (4 pounds). You would then look at mixed liquid density, also known as weight per gallon, to determine how much material to order. Most of VFI’s rubbers, with the A and B sides combined, are 8-9 pounds per gallon. Because VFI’s rubbers come in 1-gallon kits, 5-gallon kits, drums, or totes, we’d recommend a 1-gallon kit of material for this specific project.

Note: Many people have poured water into their mold box to determine how much material they need. However, this can be risky because urethane is sensitive to moisture. Getting your mold box and models wet can cause adhesion, curing, and bubbling issues. Some models will be very porous, so ensuring they are dry and sealed properly before pouring the rubber is essential.

Accounting for Waste

Material can be lost through accidental spills or as it clings to the sides of mixing containers and mixing equipment. Since waste occurs, it is recommended to add 5-10% more material to your estimate.

In most cases, having more material saves time and money when accounting for this waste. If you don’t have enough material, it might disrupt the mold-making process and create more waste than anticipated.

Contact VFI if you need further assistance determining how much rubber you need to make your molds.

The two most common spray methods VFI hard coat products utilize are Qwik Spray and high pressure spray. Spraying, in general, provides applicators with several advantages – speed, uniformity, and reduced labor costs – compared to roller and brush applications.

Those new to spraying can benefit by starting with a cartridge-based applicator. However, it can also be hard to know if it is the best application method for you. There may come a time when your production line could benefit from upgrading to a high-pressure spray rig. Maybe you started making small displays and signs for retail stores but have recently been contracted for bigger work by theme park and attraction companies. VFI has excellent technical and customer service support to guide you when making this important decision.

Note: Always wear proper protective equipment (PPE), including an approved respirator, regardless of what equipment you’re using. Also, utilize a well-ventilated spray booth where necessary.

Qwik Spray Gun Requirements

VFI- 70 D Qwik Spray Hard Coat is the cartridge-based polyurethane formula VFI recommends for protecting smaller EPS theming elements. To use the material, you will need a VFI- Qwik Spray Gun capable of holding 750 mL dual cartridges, an air compressor that supplies clean, dry air at a minimum of 100 psi and 10 cfm of constant pressure, and GS-15 Static Mix Tips.

VFI- is stored in cartridges with two separate chambers for the A (Iso) and B side (Poly) materials. The design of the cartridges ensures a precise 1:1 mix ratio by volume that achieves a quality protective finish. Once the trigger is pulled, the components are pushed into and mixed through the static mix tip, which initiates a chemical reaction that cures the material after it exits the tip. The GS-15s have an 11-inch mix tip with a 3/8-inch inner diameter, which creates a fine texture on surfaces.

High Pressure Spray Rig Requirements

VFI- 70 D Spray Hard Coat is the high pressure polyurethane formula VFI recommends for protecting larger EPS theming elements. To use this material, you will need a two-component air, electric, or hydraulic sprayer that runs at a minimum of 150-155°F and 2,500 psi of constant pressure, with heated lines. Some spray rigs that accommodate these requirements are:

• Graco A-XP1 air sprayer
• Graco Reactor 2 E-XP2 electric sprayer
• Graco Reactor 2 H-XP2 hydraulic sprayer
• Graco Reactor 2 H-XP3 hydraulic sprayer
• PMC PHX-2 hydraulic sprayer
• PMC PHX-25 hydraulic sprayer

Advantages of Using the Qwik Spray Gun

1. Portability

A big reason the Qwik Spray System is so desirable to many users is because all you need is the lightweight applicator and enough cartridges to cover your piece at the desired thickness. Since this method is typically recommended for smaller projects (under 90 square feet), you’ll probably only need a kit of material, which is just 6 cartridges. With improved portability of the material and equipment, you can go from job to job much easier and aren’t held down to a single location for spraying. Note: This will also be dependent on the size of your air compressor.

2. Cost-effective for Small Projects

If you’re spraying small sculptures, custom signs, scenery, or props for a museum, retail store, theater production, etc., the VFI- formula is preferable. Small projects typically include pieces 4 feet x 6 feet and under. Anything over this size will generate a large amount of overspray. Other small jobs this material can help with are if you need to repair an existing hard coat that has become damaged or adhere large EPS pieces together for a larger project.

The Qwik Spray Gun is more affordable, and while the material might cost more, you’ll save a lot on equipment if you’re not hard-coating massive theming projects. If you want a quality spray rig, they can cost upwards of $20,000-$80,000 or more. The higher end would be for mobile rigs with compressors and generators, so your spray equipment is easier to transport.

3. Better for Minimal Spraying

Many applicators can’t justify the price that comes with high pressure machinery if they are not spraying frequently. The Qwik Spray System is a great alternative if your production only calls for spraying a couple of times per month. However, there are situations where applicators have justified upgrading even if they only spray once a month.

Someone might eventually switch to high pressure if their spray load increases substantially, as they would save upwards of 60% in material costs if they switched from Qwik Spray. Two cartridges are just under a gallon of material and are significantly more expensive than purchasing in gallons or drums.

4. Limited Training Necessary

Another reason users desire the cartridge-based applicator is due to ease of use. Because the machinery is less advanced, applicators don’t need as much training to use it. If you’re new to the Qwik Spray System, check out our how-to-use guide with pictures for easy assembly and tips on spraying.

VFI recommends this spray applicator to get users started when they don’t have any previous experience. It allows applicators who are used to applying coatings with brushes or rollers to experience a low pressure version of spraying. Note: If you’ve never sprayed before, it will take some practice to achieve a consistent, desirable finish.

5. Low Maintenance

A big perk about cartridge-based spray application is that there are no spray lines to clean after spraying. Empty cartridges and static mix tips can be thrown away after use, so there’s limited mess and maintenance. The cartridge-based applicator does not require frequent use to keep it in working condition.

On the other hand, high pressure spray equipment requires a lot of maintenance to prevent downtime from chemical buildup, corrosion, and other factors. You have to clean spray nozzles, pumps, lines, etc. frequently. VFI offers VFI- Pump Flush for cleaning spray lines to prevent material from clogging the equipment. It also has more parts that can wear over time, so it’s important to inspect and replace them to ensure your equipment is in working order.

Advantages of Using a High-Pressure Spray Rig

1. Better for Increased Project Volume

If you’re suddenly spraying almost every day vs a couple of times per month, it may be time to upgrade to a high pressure spray rig. As mentioned, the material costs for a cartridge-based system are more substantial. When you start to notice that you’re buying cases upon cases of cartridges, switching over to drums or totes can make a huge difference.

Are you interested in learning more about catalyst for pu grouting? Contact us today to secure an expert consultation!

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Note: High pressure spray rigs must be used often to keep them in working condition. If you do not have plans to use the spray rig, you should flush the spray lines so that coating residue is not left to solidify or crystallize.

2. Better for Versatile Spraying

When you have a high pressure spray rig, there’s no limit to the types of jobs you can work on. Whether your carved EPS structure is small, medium, or large, the spray rig will accommodate it.

Another thing that makes high pressure rigs so versatile is that they can be used with different materials. Polyurethane and some hybrids are typically the only material that can be used with cartridge-based equipment. If you’re looking for a material that’s a bit softer than a polyurethane or hybrid coating for your theming project, high pressure polyureas have been used in their place.

3. Better for Fixed Location Spraying

While the portability of the Qwik Spray Gun is desirable, if you’re not going on-site to spray a hard coat, that portability doesn’t always matter. Many theming designers have workshops where they do it all: carve shapes and forms, spray hard coats, and paint over them. These shops typically also have a designated spray booth to contain overspray and protect their work environment and workers from harmful spray fumes.

4. More Control While Spraying

A negative part of the application process when using a Qwik Spray Gun is once you start spraying, you’re not supposed to stop. Continuous spraying is necessary because if the flow is stopped, the coating will clog up in the static mix tip. You need to plan your spray route ahead of time for a consistent, uniform finish. If you want to stop, you’ll have to switch applicator tips before you start again.

With a high pressure spray rig, you can start and stop when you need to. Having control also reduces the amount of material used, so there’s less waste.

5. Improved Cured Surface

Something that tends to be insignificant to some applicators but can save on time and labor costs is how the coatings cure. The high pressure hard coat formula comes out smooth, seamless, and free of blemishes due to the pressure and speed at which the coating exits the applicator. It has less time to interact with the environment, which could cause potential issues.

The Qwik Spray formula, on the other hand, is slower and doesn’t come out of the applicator with as much force. This gives it more time to interact with the environment, which creates a foaming effect from moisture in the air. While the surface irregularities aren’t that noticeable, it will be more textured. This might create more post-work, such as sanding before the application of a top coat can occur.

Contact VFI if you’re still trying to determine whether the Qwik Spray or high pressure hard coat is better for your unique project.

How to Use a Brushable Hard Coat + Testing for Recoat Window

Knowing how to use a brushable hard coat can save you money on labor costs and material waste. Before you begin working with new materials, always read the labels on the supplied containers. If it is difficult for you to read the labels, VFI offers technical data sheets with thorough instructions on every product page under resources.

If you’ve never worked with a brushable hard coat, you can also check out our detailed how-to video here.

Through this article, we will provide various tips for using one of these products. An important aspect of using a brushable hard coat is adhering to the recoat window. So, we also wanted to show you how we test for that.

Preparing Your Foam for Hard Coating

Typically, users apply these coatings to EPS foam. We recommend 2 PCF foam for the best cost-to-quality ratio. Allow the foam to age for 30 days minimum before coating it.

After carving the foam, it must be free of particles that might disrupt adhesion. Clean off the piece with a vacuum or compressed air. Also make sure the piece isn’t damp as this could also affect adhesion.

PPE for Applying Brushable Hard Coats

VFI recommends using personal protective equipment, including gloves, long sleeves, and safety glasses, when working with these materials. Please see the material SDS for more information.

Even though the coating is not sprayed, a respirator is required when sanding. Inhaling or ingesting these materials as particles can be toxic.

If you have a spray booth, it’s a good idea to work inside it while sanding. The fans will help keep the sanded hard coat particles inside the booth and away from your facilities.

Preparing Your Workspace

First off, these materials are sensitive to moisture. It is highly recommended that you work in a temperature-controlled environment around 72°F with low humidity.

If you don’t, bubbles will accumulate during mixing and application. These bubbles will then cure on and in the finished surface. The entire piece will require sanding and a new coat, depending on your desired finish.

Measuring the Materials

These are two component materials with a mix ratio of 1A:3B by volume. Since the B side is thicker and more of it is needed, we recommend measuring that material first. It’s much easier to pour the A side into the B side when ready.

We also recommend measuring how much of each material you need by weight rather than by volume. To do this, you will need an accurate gram scale. It helps you avoid making errors that could occur when measuring by volume.

Another tip when using these coating materials is to never use a full kit of material. Doing so will shorten the working time, which includes the time it takes to mix and apply it.

• VFI- 75 D Brushable Hard Coat has a mix ratio of 1A:3.44B by weight. To make calculations easier, we recommend using 100 grams of A side to 344 grams of B side. For an even smaller amount, use 50 grams of A side to 170 grams of B side.
• VFI- 65 D Brushable Hard Coat has a mix ratio of 1A:3.55B by weight. To make calculations easier, we recommend using 100 grams of A side with 355 grams of B side. For an even smaller amount, use 50 grams of A side to 175 grams of B side.

Note: when you’ve set aside the material you will be using, nitrogen purge both containers before closing them to extend the life of the unused material. You can find nitrogen purge kits on Amazon if you don’t have one readily available.

Mixing the Components

The second the materials touch, a reaction occurs, and the pot life begins. You’ll want to mix them using the double-bucket mix method. We recommend using a 1-gallon paint stir stick. You can find them at any home improvement store. Make sure to scrape the sides and bottom of the mixing container. Once you are done mixing in one container, pour the material into a new, clean mixing container and mix again.

It’s somewhat easy to tell when you’re done mixing because of how different the materials look. The Iso (A side) is very dark, and the Poly (B side) is very light. When the combined material is a uniform, neutral color, you’ve probably mixed it thoroughly and can begin applying it. You don’t want streaks of either material in the mix; otherwise, areas in the coating will be tacky and may never cure.

Applying the Brushable Hard Coat

When applying the material, use a non-shedding chip or foam brush. You can use a roller if you desire, but it must be a sponge roller, not a nap roller.

If you’re applying it to non-horizontal surfaces, you’ll want to wait a few minutes for the material to thicken so it doesn’t drip. If the coating does sag, you must sand it for a smooth finish.

Apply at least 60 mils to ensure a uniform film. Use a mil gauge to test the thickness of the layer.

If you plan to apply additional coats, you must stay within the recoat window. VFI- has a recoat window of 4 hours at 50 mils. If you apply it at a greater millage, it may affect the recoat window. If you miss the recoat window, you must sand the coating before applying another layer.

Setting up to Test VFI- for Recoat Window

While on the topic of recoat windows, we wanted to explain how we would test for this property. The test method is arbitrary, so there is no industry standard.

A recoat window is the time after an initial coating has been applied that a secondary coating can then be applied, ensuring a strong bond between the two layers.

For the test, we mixed up small batches of the VFI-. To ensure we had a sufficient amount of material, we used 206 grams of Poly (B side) and 60 grams of Iso (A side) by weight.

We applied the coating to a pre-sanded board of VFI- 70 D EPS Form Hard Coat, which is a similar urethane hard coat. We spread the brushable coating onto the board at 50 mils thick with a square film applicator.

The temperature was 75°F with a relative humidity of 70%. Because the humidity was so high, we immediately noticed bubbling in the mixing cup and the coating as it started to cure on the surface. This wouldn’t affect what we were testing for, but it is something to avoid if you want a smooth, bubble-free finish.

We didn’t think we would get good results if we tested the material in half-hour intervals at the start, so we applied a second 50 mil coat after the first had cured for 1 hour and 2 hours. These second coats were applied at 79°F with a relative humidity of 66%.

We also coated a second board to test in half-hour intervals from 2.5 to 4 hours. The first coats were again applied at 50 mils with the square film applicator. The temperature was around 71°F with a relative humidity of 70%. With the humidity still around the same as the first board, we noticed bubbling in the coating again.

We then applied another 50 mils on top of the first coat after it had been curing for 2.5 hours, 3 hours, 3.5 hours, and 4 hours. Note: A 5-hour test was also tacked on since we had room on the board.

The temperature was between 70-71°F with a relative humidity between 70-76%. The new layers also started to bubble. Increased bubble formation may have occurred because the previous coating was still off-gassing as well.

Testing Adhesion for Hard Coat Recoat Window

We left the boards to cure for the rest of the day before we could prepare them to test their intercoat adhesion for the recoat window.

The surface was sanded before we applied dollies from the Elcometer 106 Pull-Off Adhesion Tester to each test section with an epoxy adhesive. We left the adhesive to cure for 3 days to ensure the dollies were firmly attached to our testing surfaces.

With the dolly cutter (bimetal hole saw), we cut around the base of the dolly so lateral bonding wouldn’t interfere with the test. We then removed the excess coating and adhesive shavings.

The base support ring was placed over the dolly to ensure a flat surface. The tester claw was then clamped onto the dolly, and the wheel on top of the tester was tightened to apply a perpendicular force that would pull the dolly off. The indicator on the tester retains a PSI value at which the coating separates from the surface.

Results of the Recoat Test

We wanted to see two things from the pull-off test:

• An acceptable PSI for tensile strength
• The two coatings still adhered together

If we only saw one layer of coating and/or a low PSI, that would be a failure.

The 3.5-, 4-, and 5-hour samples failed at 200 PSI, while the 2.5- and 3-hour samples failed at 400 PSI. The 2.5- and 3-hour samples maintained intercoat adhesion, which was a success. While the 5-hour sample failed at 200 PSI, it maintained intercoat adhesion.

That’s how we determined that a second coating could be applied at 50 mils up to 4 hours after the first. We also determined that reapplication 1-2 hours after applying the first coat is not recommended. The recoat window can always change depending on the film thickness, application surface, and temperature.

Applying VFI- after 4 hours will compromise the adhesion between coats. After this time, the initial coat would have to be sanded and/or primed before another could be applied.

Contact VFI if you need more assistance when applying multiple coats of a brushable hard coat.

Differences Between Silicone, Latex, and Urethane Molding Rubber

Learning the differences between silicone, latex, and urethane molding rubbers can help you determine which material is best for your next project. Regardless of the material you choose, they are all flexible and capable of producing highly detailed, durable molds. Their unique features can make one better for a certain application compared to another.

What Is Silicone Rubber?

Silicone is a synthetic rubber used to make brush-on or pour molds. It is a two-component material, and these parts are combined to cause a chemical reaction that converts the liquid into an elastomer.

Its main structure is composed of siloxane chains (silicon and oxygen). The manufacturer can adjust these chains to enhance the rubber’s properties for a desired project.

It is the most expensive rubber molding material. There are two common catalysts used to cure silicone:

Platinum-based

This type of silicone is also known as addition curing and uses a platinum catalyst. It’s a premium molding rubber that lasts longer than tin-based silicone but is also the most expensive.

This material can be formulated for various uses, including brush or pour application, skin-safe application, or food-safe projects when needed. Little shrinkage occurs when making molds, plus the material has great temperature stability and chemical resistance.

Tin-based

This type of silicone is also known as condensation curing and uses a tin catalyst. The tin catalyst makes it less expensive than platinum silicone.

It is used for general mold-making and prototyping, but it is not as long-lasting as other materials. As it ages, it will wear, lose elasticity, and become brittle.

Unlike platinum-based silicone, it is not prone to cure inhibition and can be used with most materials. It can create fine and intricate details for polyester, epoxy, gypsum, wax, concrete, and plaster casting. However, it is not suitable for skin application, even after curing.

It is prone to shrinking over time and as it cures. Its shrinkage partially comes from the release of methanol during the reaction. So, the bigger the mold, the less stable it will be. Fillers can make it more stable, but it will lose tear strength and become heavier.

Benefits of Silicone Rubber

• Its most appealing feature is that it does not require a release agent, so it demolds easily from most materials. It will also be able to withstand several casts without wearing significantly.
• Silicone can have varying properties, including Shore hardness, elasticity, working times, and curing times. This versatility makes it easier to choose one that meets your needs.
• Silicone is mostly formulated on the Shore A hardness scale. A lower hardness and ability to replicate details make them a great choice for historic restoration. There is a reduced chance of damage to the original or master.
• Regardless of where you need to make your molds, silicone works well for molding on or off-site. Various formulas offer fast cure times for easier in-field molding.
• It is not sensitive to moisture, so you can work in various conditions without worry of bubbles forming in your mold.
• It is desirable as a brush-grade material because it gets thicker better than urethane. Brushable formulas also replicate complex designs for specialty projects more easily. It is best for creating what’s known as a skin or glove mold. These molds will need wood or plaster backing.
• If you need your mold to withstand high temperatures, silicone works better in these environments.

Cons of Silicone Rubber

A downside to using silicone molds is that with repeated use, they will not last very long. Depending on the mold, they start to disintegrate or tear. They also lose their detail over time.

Because of cost, silicone molds are usually made with mold boxes or additional support, which will take added time and experience to develop.

These molds have poor abrasion resistance, so they’re not always recommended for casting concrete or materials like it. If you cast concrete, they work for low-volume production.

What Is Latex Rubber?

Latex is naturally sourced from rubber trees and was the first widely used rubber. It’s typically composed of rubber particles, water, proteins, and sugars, which all work together to provide a unique set of properties.

Compared to other molding rubbers, it is a thin material that can be brushed onto surfaces or sold as a sheet good. A brush-on mold can be desirable compared to solid molds as it saves on material costs.

Unlike other room-temperature vulcanizing rubbers, latex cures by evaporating the water and ammonia in its formula. Once cured, it leaves a highly elastic, durable mold that replicates perfect detail.

Benefits of Latex Rubber

• It’s the most affordable molding rubber and is extremely durable, so you benefit from a more cost-effective, long-lasting product.
• It has good strength, tear resistance, and flexibility, which all contribute to its longevity. It will last a long time in production if maintained and stored properly.
• In terms of ease of use, as a single-component material, it does not require measuring and mixing. Like silicone, little or no release agent is required to prepare the molding surface. It’s also water-based, so cleanup is easier and faster.
• Due to its abrasion resistance, it is good for casting abrasive materials like concrete and cement as well as wax and plaster. It is perfect for making flat molds for ornamental concrete projects like stone veneer and two-dimensional architecture. It can also be used for limited resin casting.
• Like silicone, it makes a good thin-walled glove mold but cannot be applied to the skin during or after application. By applying it with a brush, you can create molds with irregular shapes or very intricate molds with fine details.
• It is biodegradable, which makes it more environmentally friendly. This also means that, over time, when exposed to the elements, it can rot, degrade, and crumble.

Cons of Latex

Latex has a strong ammonia smell, which is undesirable during the extensive application process. When it’s not in use, it has to be stored at room temperature. If it freezes, it is unusable and must be disposed of.

While latex is strong, it has a high shrinkage rate as it cures. It can shrink as much as 10-20%, which causes it to lose fine details. It’s generally not recommended for casting urethane, polyester, or epoxy resins.

Because this material is used to make thin-walled glove molds, it requires rigid backing or a support mold. An unsupported latex mold will deform and stretch out of shape while casting.

Like silicone, certain materials can inhibit its cure like Vaseline and sulfur-based clay. Touching the surface of one latex layer before you add another can prevent it from curing. It’s also known to cause allergic reactions in some people upon skin contact.

Even though it is the cheapest molding rubber option, its multiple thin layer application method increases labor costs. Since only one layer can be applied at a time, and many coats are needed, it may take several days or weeks to make a single mold.

What Is Urethane Rubber?

Urethane rubber is another synthetic molding material for use in a variety of molding and casting applications. Like silicone, it is 2 part rubber that must be measured and mixed accurately. The chemical reaction occurs between an isocyanate and a poly. It is best for concrete casting.

Polyurethane is an affordable molding material. It is also more versatile because it can be formulated into different materials like plastics, foams, and coatings. It ranges between the A and D Shore hardness scale to accommodate various application needs.

Benefits of Urethane Rubber

• It has excellent physical properties that make it tougher than other molding materials. High properties include elongation and tensile strength for extended wear and tear, which are also customizable to meet specific performance requirements.
• Urethane is more dimensionally stable than silicone or latex, which means low shrinkage when making molds. It also maintains stability after substantial pressure is applied for consistent castings.
• It is more versatile than silicone or latex. Due to its range of property options, it’s used for a wide variety of projects. It can be formulated harder than other rubbers, which is better for tooling projects like stamps and formliners.
• Because it is highly durable, it can be reused over and over, especially in abrasive applications. Its reusability makes it the best material for high-volume production.
• Its ability to transfer pigment is better than other molds, which makes the color of the casting more vivid. It’s also more friendly to in-mold coatings and other modifications like painting. This ability is important to enhance the look of casting materials.
• Since urethane molds are thicker and solid, they typically don’t need rigid backing like silicone and latex glove molds. However, wood backing can be beneficial for large, flat molds to prevent shrinking in extreme temperatures.
• While release is required to prevent urethane from sticking to other surfaces, VFI offers a line of urethane rubbers that demold more easily. They have best-in-class release characteristics and are proven to lower breakage rates by 80%. This can be especially beneficial when demolding from delicate undercuts and details.

Cons of Urethane

The biggest downside of urethane rubber is that it requires a release agent before casting. It is highly adhesive and will bond to any surface. When making the mold, porous surfaces, including wood and natural stone, also have to be sealed properly.

Another downside of urethane is that it is moisture-sensitive in its liquid form. This can make it hard to work in warm and humid environments. If moisture finds its way into the mixture, it causes bubbles to form, which may affect your final mold surface.

Which Molding Rubber Should I Use?

What material you choose depends on several factors, including:

1. What is your budget?
2. What is your model or master made of?
3. What properties do you require? (i.e., high tear strength, high hardness)
4. What level of detail do you require? (i.e., extreme vs simple detail)
5. What material are you casting into the mold?
6. How many castings do you need to produce, or how long do you need your mold to last?

Molding Material Comparison Chart

Urethane Silicone Latex Application Pourable Pourable and brushable Brushable (needs 12-20 coats) Cost Cost-effective for high-volume production Highest upfront cost, depends on catalyst Most affordable Composition Two-component Two-component Single component Cure time 16-24 hours 4-24 hours 1 hour per coat; 24-72 hours after final coat Ease of use Mixing can be difficult, and release is required Can be difficult to mix, but release is not required Time-consuming to apply, but release is not typically required Wear resistance Very durable and reusable for abrasive casting Durable but wears over time when used with abrasive materials Most durable but can degrade over time Casting materials Concrete, plaster, wax, and other abrasive castings Concrete, plaster, wax, urethane and polyester resin castings Concrete, cement, wax, and plaster castings Storage Stability Does Not Freeze Does Not Freeze Will Freeze

Understanding the Properties of Industrial Polyurea and Hybrid Coatings

Understanding the properties of industrial polyurea and hybrid coatings is essential for proper use. Some industrial coatings enhance or protect surfaces, while others improve something as simple as aesthetics. Polyurea and hybrids are used almost solely for their protective purposes. VFI compiled information about the most important properties of these materials so you are better equipped to choose the right one for your project.

What Physical Properties Are Important?

When it comes to properties, there is a bit of a difference between polyurea and polyurea hybrids. Pure polyureas tend to have consistently higher physical properties than hybrids. However, both vary by formulation.

There are certain applications where polyurea is more desirable, such as environments where moisture is a concern. If moisture isn’t a concern, hybrids still have advantages and can be more cost-effective. The following physical properties are important to know regardless of coating type:

Shore Hardness

Test method: ASTM D

Definition: Shore hardness tests the resistance of a material to localized deformation or indentation. The material is tested using a durometer tool and is ranked on different scales between 0-100. Which scale is used is determined based on the material’s qualities.

Importance: Hardness is an adjustable property. Materials can come in different hardnesses to suit a customer’s needs. Industrial coatings will protect underlying surfaces when the correct hardness is chosen based on the specific application.

Polyurea or hybrid coating hardness is typically measured on the Shore A or Shore D scale between 40 A and 80 D. Materials on the A scale are typically softer, while materials on the D scale become much harder. For example, VFI-270 70 A Polyurea Spray Coating will be more flexible and rubber-like, while VFI- 68 D Polyurethane Spray Coating will be more firm and almost plastic-like.

A harder material is desirable for its resistance to scratches, dents, or gouges from abrasion. This is important in applications that experience daily wear and tear, such as truck bed liners, secondary containment, speaker boxes, table edging, and more. Lower hardness provides more flexibility and is desirable for applications like reinforcing foam for amusement ride padding due to higher impact resistance.

Polyurea and hybrids typically offer a good balance between hardness and flexibility to prevent cracking. They can bear weight or maintain their shape under various stresses. They will also resist punctures and penetrations.

Note: Most VFI products will have their Shore hardness in their name, specifying whether they are on the A or D scale, to make it easier to find what you’re looking for (ex. VFI-200 50 D Slow Polyurea Coating vs. VFI- 70 A Polyurea Hybrid Spray Coating).

Tensile Strength

Test method: ASTM D412

Definition: Tensile strength is a property that tests the maximum pull a material can withstand without tearing or breaking when being stretched. It is expressed in pounds per square inch (psi).

Importance: High tensile strength increases a coating’s ability to resist pulling forces, providing a higher tolerance to stress.

Good tensile strength is essential where surfaces experience impacts, expansion, contraction, or vibrations. In the instance of impacts, high tensile strength will help absorb the impact energy and prevent damage or deformation from occurring on the surface.

Like hardness, tensile strength also works with flexibility. A highly rigid coating could be prone to cracking, even with impressive tensile strength. That’s why polyurea and hybrids often offer a balance between all these properties to prevent failure. Certain hybrids might have a lower tensile strength, but this can be the trade-off for other desired properties like increased elongation.

Elongation

Test method: ASTM D412

Definition: Elongation is tested with tensile strength by stretching a material and measuring the increase in length it will achieve before breaking. It is expressed in a percentage (%) of the original length.

Importance: Industrial coatings can have high elongation, which is important for applications that encounter impact. Polyurea’s inherent flexibility is a factor that contributes to its ability to elongate and move with the surface without cracking or losing adhesion. They are formulated to be strong and flexible, which is dissimilar to other coatings that may break from movement or vibration. Elongation can also help absorb impacts, which is beneficial for applications like truck beds, recreational vehicles, trailers, or work trucks.

A higher elongation will mean a lower tensile strength, which makes it more elastic than rigid. If it is highly elastic and stretches easily, it might lack the hardness needed for certain applications. Polyurea offers a good balance of elongation with other properties to provide desired flexibility and durability. Hybrids might have lower elongation, but this can be made up with other higher properties.

Tear strength

Test method: ASTM D624 C

Definition: Tear strength tests the maximum force required to start a tear in a direction perpendicular to the stress. It is also known as tear resistance and is expressed in pounds per linear inch (pli).

Importance: Tear strength is another critical property for coating users. It tells you how well a coating will resist tearing and maintain its integrity as a protective barrier. High tear strength will prevent small punctures and abrasions from turning into large tears that could compromise the coating’s ability to protect the surface.

Even in an application with abrasive wear, the higher tear strength will prevent minor abrasions from turning into large tears that expose the underlying surface. In the event of impact damage, tear strength prevents the development of tears from a forceful blow.

Polyurea provides good tear strength and flexibility. Hybrids may have lower tear strength, but what they lack in one property, they can make up for in another one.

Water Absorption

Definition: Water absorption is the amount of water absorbed by a material. It is measured as a percentage (%) of the weight of water absorbed to the weight when dry. It can also be called moisture absorption or water swelling.

Importance: One of the most desirable uses for industrial coatings is waterproofing. They produce a seamless, impermeable barrier, preventing moisture from reaching the underlying surface. You will see a low percentage (under 5%) of water absorption if the material works well as a water-resistant barrier.

Polyurea and hybrids are non-porous, which helps prevent them from absorbing liquids. If water is absorbed and then freezes, it will expand and cause the coating to crack. High water absorption can also cause swelling, which results in dimensional change, loss of strength and adhesion, delamination, or fracture.

Water absorption will also tell you if a coating is suitable for interior and exterior use. A low absorption rate is necessary in outdoor applications, especially in climates with heavy rainfall or freeze-and-thaw cycles. If it has low water absorption, its strength and durability will be maintained over time with water exposure.

Water Vapor Permeability or Permeance

Definition: Water vapor permeability is the rate at which a material allows water vapor (water in its gas form) to pass through. It is stated in perms and is often also called permeance or breathability. Lower numbers indicate a lower permeability. It is not directly related to water absorption.

Importance: Along with water absorption, permeability can impact the performance and durability of coatings in waterproofing applications. A high permeability controls the rate at which water vapor passes through, preventing moisture build-up that could lead to mold growth, blistering, bubbling, and delamination.

Low permeability can also prevent corrosion, discoloration, and other forms of damage. If a coating with high permeability is applied to a metal surface, trapped moisture could accelerate the formation of rust. If the coating is breathable, the water vapor can escape, reducing corrosion.

Permanent Set

Definition: Permanent set refers to a point where irreversible deformation of the material occurs even after stress is removed. The property is recorded as a percentage of the total deformation compared to the original length.

Importance: Permanent set can be affected by various factors, including the type and amount of stress applied, temperature, and stress duration. Knowing a material’s permanent set will help you understand its behavior and properties under stress. It can be reduced by using materials with higher strength and stiffness and by controlling the temperature and duration of stress.

Cold Temperature Flexibility

Definition: Cold or low temperature flexibility is the ability of a material to resist cracking when flexed in low temperatures. This property is not listed for every material but will receive a pass or fail as a test result.

Importance: Though temperature and weather are out of our control, manufacturers can control how well their products hold up in these conditions. Polyurea and polyurea hybrids are unique because they withstand the fluctuating temperatures of various climates. Even in low temperatures, these coatings can maintain their durability and properties. Other materials might have impressive strength, but they can become brittle at low temperatures, which leads to cracking or failure.

Good cold temperature flexibility means the coating has enough flexibility and elongation to stretch without breaking over a mandrel bend. Flexibility is essential for the coating to expand and contract with the surface in low temperatures.

Adhesion Strength

Definition: Adhesion strength measures a coating’s resistance to separation from a surface when perpendicular tensile force is applied. It may also be called bonding strength. It is expressed in pounds per square inch and is typically tested for prepared steel and concrete surfaces.

Importance: Adhesion is one of the most, if not the most, important properties for a coating. It ensures that the material will adhere to the surface for long-term protection. It will do so even in the most aggressive conditions.

Polyurea or hybrids have excellent adhesion to several substrates, including concrete, steel, foam, and wood. Bonding increases with proper surface preparation. Cleaning the surface is always necessary to prevent adhesion failure. While not always necessary, priming the surface can provide the best adhesion results. Factors that may cause poor adhesion include temperature, cure time, moisture, and inadequate surface preparation.

Poor adhesion can cause peeling, flaking, blistering, and delamination, allowing substances to penetrate underneath. It can compromise the coating’s effectiveness in waterproofing, impact resistance, chemical resistance, and other properties. These problems can be costly to fix, so you’ll want to find a coating with good adhesion to your specific surface.

What Liquid Properties Are Important?

Unlike most manufacturers, VFI differentiates between physical and liquid properties. This differentiation helps tell you which properties pertain to the coating when it is in its liquid state vs its solid, cured state. Liquid properties help more during the application process, while physical properties tell you how it will perform throughout its lifespan. The following are important liquid properties:

Solids by Volume

Test Method: ASTM D

Definition: Solids by volume is a measure of the total volume that remains on the surface once the material cures, expressed as a percentage (%).

Importance: Low solids content means there is solvent within the product. Solvents evaporate as the coating dries and can be harmful to applicators since they may be volatile organic compounds (VOC). The evaporation of the coating significantly reduces the amount of material that cures on the surface. That’s why several coats must be applied to have the same thickness as a 100% solids coating.

A coating with high solids will have a higher concentration of solid components. They are more environmentally friendly because little to no solvents are emitted during cure. Also, they maintain the same level of thickness once cured. Not having to apply multiple coats means less material and less time are needed during application. There’s also a reduced risk of adhesion problems if extra coats are not required.

A great characteristic of polyurea and hybrids is that most are 100% solids. This makes applying them much easier because you know the amount of material you are putting down is the amount of material that will remain. You don’t have to worry about applying or buying more material to make up for the thickness that would evaporate if you used a low solid coating. Also, because there are no solvents, this contributes to a faster cure for reduced downtime and quick turnarounds.

A common misconception is that all solvents are VOCs. A common solvent that disproves this is water and it contains no VOCs. A solvent is part of the total solution and acts as a carrier for the entire system.

Mix Ratio by Volume

Definition: A mix ratio is assessed for liquid materials that require two or more components to be mixed together to produce a chemical reaction that will allow them to cure. Mix ratio by volume uses exact proportions, expressed as a ratio (ex. 1A:1B), measured using equal-sized containers.

Importance: Some coatings may have a mix ratio by weight, but due to the speed of polyurea and hybrids, there is not enough time to mix them together before they cure. They are applied by high-pressure spray rigs where the material is pumped through lines and mixed right at the gun tip so the reaction can occur without clogging the lines or gun.

Exact mixing proportions must be followed for proper curing. Too much or too little of one component can inhibit the cure. It might feel too soft or sticky and won’t offer the desired properties to protect a surface. It might never develop full physical properties, which wastes time and material if reapplication is necessary. Being off ratio could also affect adhesion and lead to peeling, flaking, or delamination from the surface.

Viscosity

Test method: ASTM D

Definition: Viscosity measures the resistance of a liquid to flow, or rather, the relative thickness/fluidity of a liquid. It will be listed on a technical data sheet in centipoise (cps) for each liquid component and sometimes for the mixed material. To better understand viscosity, below is a list of household items and their relative viscosities:

Material Viscosity Water 1-5 cps Blood 10 cps Corn syrup 50-100 cps Maple syrup 150-200 cps Castor oil 250-500 cps Honey - cps Molasses - cps Chocolate syrup - cps

Importance: Viscosity can directly affect how a coating behaves during application. Because polyureas are applied by high pressure spray, they are most desirable at a lower and similar viscosity. The lower viscosity is desirable because it enhances the workability of the coating and makes application easier. The speed at which they are applied and their low viscosity can also reduce the amount of trapped air in the finish.

Low viscosity is also needed to evenly distribute the coating for smooth and uniform application. A higher viscosity would be desirable for brush applications because it prevents dripping and sagging.

Polyureas will not typically list a mixed viscosity. It’s hard to assess the combined viscosity while it is still a liquid because it cures quickly once combined.

Gel Time

Definition: Gel time is the time it takes for a material to stop flowing or become gel-like. A tack free time might also be listed for some products. Tack free is when the material is no longer sticky.

Importance: Polyureas and hybrids are incredibly fast setting, so their gel time typically happens within seconds of application. The speed is desirable for most users because the faster they gel, the quicker they cure and can be placed into service.

Their fast reaction time also means they are less likely to react with humidity and moisture in the environment. Low sensitivity to moisture allows them to be applied over cold or damp steel, concrete, wood, or foam surfaces.

Gel time can also affect the surface finish. As the material is sprayed, the gel time can make it come out fine and smooth or heavily textured. The texture can be further altered by adjusting the air pressure or gun tip size.

Their speed can also be a bit of a hindrance. Because they are so fast, they are a bit harder to work with. They are typically only sprayed through high-pressure rigs, and you must have adequate training to apply them effectively. The quality, thickness, uniformity, and texture may vary depending on the applicator’s experience. Sometimes, they can be slowed for a smoother flow on intricate surfaces.

Recoat Time

Definition: Recoat time is specific to coatings and is the time frame an applicator has to apply a subsequent coat or topcoat with ensured adhesion. It can also be called the recoat window.

Importance: Some coatings are applied in single passes, but multiple coats must be applied to build thickness. You must apply those extra coats within the recoat window. The longer the first layer cures, the less likely a subsequent coat will adhere to it.

If the recoat time passes, using a primer can ensure adhesion to the original coat. In some cases, roughing up the surface by sanding or grinding before applying the next coat can also increase adhesion. If you don’t adequately prepare the recoat surface, it can lead to peeling, cracking, or delamination between layers.

Place into Service

Definition: Place into service tells you the amount of time needed for a material to cure before it is ready for use.

Importance: For polyurea and hybrid coatings, the place into service time frame can be the same day (within 4-8 hours) or the next day (at least 24 hours). This is due to the speed at which they cure. Once they cure to a point where they have enough of their properties, they can be used.

The place into service time can vary based on application. If the coated surfaces will be in contact with chemicals, the material may need more time to cure. In other circumstances, such as truck bed liner, the coated surfaces might be ready for light use in a shorter amount of time, which can be desirable for faster turnaround.

Full Cure

Definition: Full cure is the time it takes for a material to develop full strength and properties for repeated daily use.

Importance: No material develops full properties upon initial cure. Most have to sit for a few days at room temperature to obtain full strength, hardness, and other properties listed on technical data sheets. This property is typically listed so users understand that failure can occur if too much pressure is put on it before it obtains its properties. Once the full cure time has passed, the material will perform as per the properties listed. Full cure can be affected by many factors, including temperature.

Where to Find Material Properties?

Once rigorous testing has been conducted on a product, our lab staff generates the physical and liquid properties. It’s important that customers can easily find properties for all our products. We list them on all technical data sheets and product pages. To find the technical data sheet, you can navigate to any product page, and it will be off to the right-hand side under the resources tab. For mobile users, the resources tab is at the bottom of the product page.

Contact VFI for more information on properties so you can find the best material for your project.

For those who have been spraying two-component polymer coatings for a while, you may be wondering if it’s time to upgrade your Qwik Spray Gun to a high-pressure spray rig. The Qwik Spray Gun is VFI’s cartridge-based spray equipment for use with specific coatings that have been on the market almost since the beginning of the company. In fact, we were one of the first to sell a cartridge-based spray system for spray on truck bedliner and EPS theming hardcoats. It has been desirable to many due to low maintenance, portability, and ease of use.

Even though the pneumatic cartridge gun comes with many benefits, there might come a time when you’ll need something else. There are several things to consider that can make the decision to switch to high pressure much easier.

Why Switch to a High-Pressure Spray System?

1. Better for Spraying Large Pieces or Areas

Maybe you started spraying small props, custom signs, truck beds, or other equipment but have since been offered bigger projects. VFI’s Qwik Spray Gun and similar cartridge-based equipment on the market are recommended for small to medium-sized projects. If you’re spraying a piece or area larger than 4×4 or 4×6 feet, a cartridge-based system will not be as efficient. The size of the project can be extended, but it is not recommended. These projects are also pretty flat, with a limited amount of detail.

Those who do use cartridge-based equipment on larger projects accept that they will encounter a lot of overspray. That overspray will cause more required post-work as the piece will probably need to be sanded, depending on the desired finish for the project. Otherwise, this can be avoided by spraying in smaller passes, but the application will be more labor-intensive and time-consuming.

2. Better for Increase in Project Volume

Another reason applicators typically stick to the Qwik Spray System is due to the amount they are spraying. This equipment is desirable for custom jobs where applicators work on one small project at a time or are only spraying a couple of times per month. It doesn’t make sense to spend money on an expensive spray rig. However, if you’re spraying more than you initially were, purchasing high pressure equipment can save you money in the long run due to material costs.

For example, businesses that spray less than 10 truck beds a month would benefit from spraying cartridges of VFI-544 Qwik Spray Bedliner, but if you’re seeing more traffic come through, you’ll probably need an upgrade to accommodate. VFI-542 High Pressure Spray Bedliner sprayed through high pressure equipment is recommended if your business is growing and you’re taking on more projects.

Also, high pressure equipment, because of the increase in pressure and temperature, cures coatings faster. A faster cure is extremely desirable for applicators who need to spray at high volumes so they can get onto the next project quicker.

3. Better if You’re in a Fixed Location

With the Qwik Spray Gun, as long as you have air pressure, you can take the equipment anywhere. However, if you’re not taking your spray gun to various locations for spray jobs, you don’t need portable equipment.

High pressure equipment is not as easily transported, which is why it’s not the go-to for many new sprayers or those who do low-scale, low-volume jobs. Once you know that the location you’re spraying at will be permanent and you have enough space, upgrading your equipment is ideal.

4. Increased Control

A downside of the Qwik Spray Gun is the lack of control when spraying. Once you pull the trigger, you must keep going until the cartridge is empty. If you were to stop midway through the application, the material would become clogged in the static mix tip because it is mixing the material as it exits.

While training is required to use high pressure equipment, once you get the hang of it, you have complete control while spraying. The trigger on the spray gun allows you to start and stop when needed. This is because a mechanical proportioner is typically used to meter out the correct ratio of material and mixes only what is necessary. It’s also desirable because it can pump, mix, and apply coatings with short pot lives very quickly.

5. Increase in Material Options

Not every material is offered in a cartridge-based format; in fact, most materials aren’t. The cartridge-based system, due to its low pressure outlet, is typically used for polyurethane and polyurea hybrid materials. However, urethane and polyurea hybrid formulas will not all work in the Qwik Spray Gun either. If you’re itching to try something new, you may need to get the application equipment to accommodate it. When you switch to a high-pressure spray rig, you get access to more materials and more formulas.

Polyurea is an incredibly fast setting material and requires high-pressure, high-temperature equipment to apply it. Cartridge-based spray guns typically only spray at a maximum of 100 psi and 10 cfm of constant pressure to push material through a static mix tip. If you use a fast material like it in a pneumatic, air-driven gun, the material wouldn’t provide a good mix without gelling and clogging the tip, so it would not have enough time to exit the gun.

6. Improved Cured Surface

While not exactly a catalyst for switching from a cartridge gun to high-pressure, there is also the benefit of having a more uniform, smooth surface. A downside of the Qwik Spray equipment is that you’ll never get as desirable of a finish as you would with high pressure equipment. Due to the lower pressure and atomizing tip on the cartridge, the material reacts more as it exits the gun. The Qwik Spray System’s reaction occurs slower, which allows the moisture in the air and the environment to create foaming. The foaming is the reason it comes out less smooth, with a bit of texture.

For example, the VFI- 70 D Qwik Spray Hard Coat is lighter and has a subtle splotchiness in its finish. In comparison, the VFI- 70 D Spray Hard Coat, sprayed through high-pressure equipment, comes out more uniform and slightly darker.

As mentioned before, if you are spraying VFI- on larger projects, it will require more post-work than a high pressure spray. If the foaming reaction is not an issue for you, it’s best to stick with the Qwik Spray Gun, especially if your project size and spray volume have not increased.

High-Pressure Equipment Recommendations

VFI manufactures polyurethane, polyurea, and hybrid materials that are mostly applied using high-pressure industrial spray equipment. We recommend finding a high-pressure, plural component spray rig that can run at 130-155°F and 2,500 psi of constant pressure with high pressure heated hoses and 10ft whip hoses. Gun tips will vary by the project and will need to be adjusted on-site. The following machines are capable of meeting these specifications:

• Graco A-XP1 air sprayer (up to 3,500 psi, 170°F, 1.5 gal/min output, & 210 ft hoses)
• Graco Reactor 2 E-XP2 electric sprayer (up to 3,500 psi, 190°F, 2 gal/min output, & 310 ft hoses)
• Graco Reactor 2 H-XP2 hydraulic sprayers (3,500 psi, 190°F, 1.5 gal/min output, & 310 ft hoses)
• Graco Reactor 2 H-XP3 hydraulic sprayers (3,500 psi, 190°F, 2.8 gal/min output, & 410 ft hoses)
• PMC PHX-2 or 25 hydraulic sprayers (up to 3,000 psi, 190°F, 2 gal/min, 210-410 ft hoses)

Graco equipment can be used with Probler P2 or Fusion guns. PMC equipment can be used with AP-2 Air Purge, PX-7 Mechanical Purge, or Xtreme Spray Gun.

Whether you’re using the Qwik Spray Gun or high-pressure equipment, you must always wear proper personal protective equipment. Also, spray in a well-ventilated spray booth whenever possible.

Contact VFI if you need technical assistance when deciding if you should make the move to a high-pressure spray rig.

Understanding the properties of urethane hard coats is essential to picking the best material for theming projects. They are designed to harden surfaces like Styrofoam or EPS foam to protect architectural shapes and forms, custom signs, and props. If you’re new to hard coatings, you may not know what properties are essential to look at compared to other coatings. VFI has put together a comprehensive guide to help you learn more about them and how they function due to their properties.

What Physical Properties of Urethane Hard Coats Are Important?

Physical properties will tell you how the material will perform when cured. Most users look at these properties to help them decide if the coating will withstand the demands of their unique project. These properties are tested using standardized methods from the American Society for Testing and Materials (ASTM). The most prominent ones listed can include:

Shore Hardness

Test method: ASTM D

Definition: Shore hardness is a material’s resistance to indentation or compressive forces. It’s measured using a tool called a durometer and rated on various scales depending on the characteristics of the material. The most common scales for polymer materials are Shore A, which rates softer materials, and Shore D, which rates harder materials.

Importance: Hardness is a property that will tell you a lot about a urethane hard coat’s wear resistance, strength, and service life. It directly impacts the material’s ability to protect an underlying surface from scratches, abrasion, and other physical damage. A harder material will give more strength, while a softer material will give more flexibility.

Polyurethane hard coats most often use the Shore D hardness scale. They will typically be in the 65-75 D range, which has a similar feeling to a plastic hard hat. When they drop below this range, they feel more flexible or rubbery. When they go above this range, they will have high resistance to deformation but can also be brittle unless they reach a certain thickness.

Achieving a good balance of hardness and flexibility while also maintaining good weathering characteristics is important. Coatings with a higher hardness have less flex and can be more susceptible to cracking when applied to surfaces that expand and contract as temperatures change. Because they have less flex, they have a limit on substrate usage and are best applied to EPS foams for theming projects. Hard coats are not recommended for surfaces softer than themselves. However, other properties can contribute to them having more flex, even at a higher hardness.

Note: All VFI EPS theming hard coats list their hardness in the product name (ex: VFI- 70 D Spray Hard Coat) to help you find what you’re looking for.

Tensile Strength

Test method: ASTM D638

Definition: Tensile strength is the maximum amount of stress that a material can withstand before it fails when being stretched. It subjects a test specimen to an applied force or load until it reaches its breaking point. That force is then measured and expressed in pounds per square inch (psi).

Importance: Tensile strength is an important property that determines if a urethane hard coat is suitable for your application. It can tell you a lot about structural integrity and durability. Coatings with high tensile strength should be capable of withstanding significant force without breaking or deforming. They are often used to protect and support delicate substrates from heavy loads. Demanding applications that would require high tensile strength include EPS foam projects within touching distance of people.

The strength of a hard coat helps it maintain its integrity under stresses such as wind, vibrations, and pressure to prevent deformation. Even small impacts can cause stress, but high tensile strength helps it absorb those forces, preventing damage from occurring.

Elongation

Test method: ASTM D638

Definition: Elongation is a property that measures the percentage (%) increase in length of a material before it breaks when stretched. It has an inverse relation with tensile strength and uses the same test method (stretching force).

Importance: Elongation is a very important property for urethane hard coats due to their rigidity. Their job is not necessarily to resist stretching force, which is why they will have high tensile strength and low elongation. However, this property ensures some flexibility and complements the strength offered by hardness and tensile strength. It is the balance of all of these properties that allows hard coats to perform the way they are designed.

Elongation will provide some necessary give to the hard coat to resist cracking even with high tensile strength and hardness. It will absorb some energy from impacts and distribute stress more evenly. Elongation with a high tensile strength also provides thermocycling capability that would not be possible with high tensile alone.

Tear Strength

Test method: ASTM D624

Definition: Tear strength or tear resistance is measured by assessing the maximum force required to tear a material in a direction perpendicular to the direction of the stress. More simply put, it is a measure of how well a material can resist tearing. It is expressed in pounds per linear inch (pli).

Importance: Tear strength is another property that can tell you about the durability and lifespan of lower durometer urethane hard coats. In a hardcoat, tear strength is a hard property to obtain unless the coating is under 65 D, but it is a good sign for thermocycling if the tear strength is high with good elongation.

After damage has been endured, the tear strength will tell you how the material will hold up. It will also tell you about its resistance to rips, punctures, and cracks. Minor nicks, scratches, and cracks can be a starting point for bigger issues if tear strength is too low. Tear strength makes the coating more resistant to damage, preventing a problem from occurring that compromises its ability to protect the underlying substrate.

Elastic Modulus

Definition: Elastic modulus is a material’s resistance to elastic deformation when stress is applied. Elastic deformation is the temporary change a material goes through when under stress, so the material will return to its original shape or size once the stress is removed. This property is expressed in pounds per square inch (psi).

Importance: Elastic modulus is a material’s ability to bear loads without significant deformation (temporary bending or indentation), which can be very important for urethane hard coats. The stiffer the coating, the higher its elastic modulus will be.

A high elastic modulus will allow it to perform effectively by handling impacts and other forces without cracking, scratching, or denting. This is because these coatings can store more elastic energy before deforming. So, the hard coat will absorb the impact energy from a blow and prevent it from transferring to the substrate.

A lower elastic modulus will allow a coating to deform rather than crack. This is useful when an object might be kicked or something sharp will hit it. It will also allow the coating to deform and not break to protect the foam. This is also important if water and outdoor elements are a concern.

Impact Resistance Unnotched/Notched Izod

Test method: ASTM D256

Definition: Impact resistance is a test that measures a material’s resistance to impact from a swinging pendulum. Unnotched Izod tests do not make a premade notch in the test specimen, so the impact energy is focused on the entire test piece. Not creating a notch will test the overall toughness of a material. The value, in pounds per inch (lb/in), will be a less accurate representation of real-world impact situations and give an elevated number. An alternative test method is a notched Izod impact resistance test with a preset notch to accurately direct the force.

Importance: Urethane hard coated projects, especially ones placed outdoors, may experience sudden forces, shocks, or blows throughout their lifespan. Impact resistance provides an understanding of whether the material has the toughness needed to protect theming applications long-term. High impact resistance will help shield the substrate from damage by absorbing the blow, preventing the coating from cracking or chipping.

Softer coatings are better at taking impacts because they have more flexibility but have a low impact strength. Usually, softer coatings will not have an impact strength tested because they will flex out of the way and provide a low number as a result. However, impact resistance is only one property that will help determine the material’s toughness. Consider the tensile strength, hardness, and elongation for a better understanding of the material’s strength.

What Liquid Properties of Urethane Hard Coats Are Important?

Not all manufacturers divide up their properties between liquid and physical. VFI does this so our urethane styrofoam hard coating users know which properties apply to the material when it’s in a liquid state versus when it has fully cured. The following are liquid properties we typically list:

Solids by Volume

Test method: ASTM D

Definition: Solids by volume or volume solids is the percentage (%) of the total volume of a material that remains once cured. In the context of coatings, it’s how much material will remain on the substrate and how much will evaporate into the air.

Importance: The amount of volume solids lets applicators know how much material they’re actually putting down, which is important when trying to build it to a certain thickness. Some manufacturers specify a millage that must be applied to achieve optimal protection, so making sure you know what you’re putting down is that much more important.

Luckily, most urethane hard coats are 100% solids, meaning no material evaporates during cure. The amount of material you apply to a surface is guaranteed to be the amount that remains once cured. Because of this, you also don’t have to worry about calculating wet and dry film thickness using the solids by volume.

Note: Be careful of shrinkage on extremely long parts as it can change depending on your thickness causing your part to warp.

Mix ratio

Definition: A mix ratio is a ratio that entails the exact measurements needed from multiple components to be mixed to produce the needed chemical reaction for a material to cure (ex: 1:1 or 2:1). A mix ratio can be expressed in two ways:

• By weight: Uses an accurate scale to measure the amounts of each component needed to cure. This property will typically only be listed for hard coats that can be applied by brush or roller.
• By volume: Uses same-sized mixing containers to measure the amounts of each component needed to cure. This property will typically be listed for sprayable and brushable hard coats.

Importance: Urethane is a very touchy material. If you don’t follow the mix ratio properly, then it might not cure to the desired effect. Adding too much or too little of one component can make the coating feel sticky or goopy rather than plastic-like when it sets. Typically, when this happens, it won’t develop physical properties, so it cannot effectively protect the substrate it is applied to. Affected physical properties can include hardness, adhesion, and resistance to abrasion or impact. The coating might be softer and not adhere to the substrate, leading to peeling or flaking.

Incorrect mixing of the components can also lead to material waste. Not only are you wasting material from each mixed component, but you may also have to scrap the entire project you’re working on and start fresh. This problem can be costly as these foam pieces take time to carve, so you don’t want to mess up.

Off ratio material will also affect the final finish of the project. When you try to paint over a hard coat that has iso-rich spots, you might be able to get away with it. However, the paint might peel off more easily when placed in the sun. When you try to paint over a hard coat that has poly-rich spots, the paint might react more with the sun and cause the paint to bubble because it is not breathable.

Viscosity

Test method: ASTM D

Definition: Viscosity is a fluid’s resistance to flow or change in shape and describes the internal friction of a moving fluid. It is often referred to as the thickness of a liquid and is measured in centipoise (cps). Viscosity can be listed for each component (A and B sides) and the material when combined. To understand viscosity, here is a list of household items and their relative viscosities:

Material Viscosity Water 1-5 cps Corn syrup 50-100 cps Maple syrup 150-200 cps Castor oil 250-500 cps Honey - cps Molasses - cps Chocolate syrup - cps

Importance: Viscosity will tell you a lot about how a urethane hard coat will perform. It determines how easily the coating can be brushed, rolled, or sprayed onto a surface. With a very high viscosity, they can be hard to spread evenly but prevent dripping or sagging. On the other hand, a material with a very low viscosity might not provide adequate coverage because it is too runny.

The ideal viscosity will depend on the application method and desired film thickness. When a material is applied by brush, the viscosity will be higher to allow easy application without excessive dripping or running. The higher viscosity also allows for better control when using this application method. When using spray equipment, lower viscosity coatings are required for even distribution, fine atomization, and a desirable finish. A similar viscosity A and B side is also highly critical to maintaining a nice even spray. Not considering the viscosity when choosing your application method can result in surface defects, such as brush marks, orange peel texture, or uneven coverage.

Viscosity affects the final thickness of cured coatings. Higher viscosity materials will generate a thicker film build, while lower viscosity materials will have thinner builds. A lower viscosity also ensures that the material can level and flow effectively to minimize imperfections in the surface finish.

Air bubbles are also typically generated in the application process. High viscosity materials are more prone to trapping air bubbles, which can create imperfections in the cured finish. Low viscosity materials allow more of the trapped air to come to the surface and escape before cure. Because the bubbles leave easier, you’ll achieve a smooth, uniform finish.

Pot Life

Definition: Pot life is the length of time a material can be used. Depending on the material, pot life can be as quick as seconds or as long as hours.

Importance: Pot life is not a property that is listed for every urethane hard coat. Since a chemical reaction happens much faster for spray coatings, you’ll see it as a property for brushable ones. It’s specific to these coatings because you need to know how much time you have to brush or roll the material onto the surface before it becomes unworkable.

Within the pot life window, your mixture maintains a viscosity for smooth and efficient application. Once the pot life ends, viscosity increases, making it hard to spread. Ensuring you have adequate time to apply the coating will minimize defects in the finish, such as orange-peel texture, air bubbles, and incomplete coverage. Also, mixing more material than can be used within the pot life leads to material waste. In some cases, mixing less material can even extend the pot life. Finding a coating with an acceptable pot life for your project is crucial for optimal protection over your theming project.

Tack Free

Definition: Tack free determines the amount of time after mixing that a material will no longer feel tacky (sticky). Depending on the material, this can happen in seconds or minutes.

Importance: Unlike pot life, this property is usually listed on sprayable coatings because it tends to happen shortly after the pot life. After a hard coat is sprayed, it needs some time to cure and become tack free so it will no longer adhere to dust, debris, or other objects that come into contact with it.

This property is essential to know for handling and assembling a coated project. If it is still tacky, it can pick up contaminants that compromise its appearance and performance. These contaminants can come from airborne dust or someone touching the surface before it has solidified enough. The material then traps these particles, marks, or smudges once cured.

Most users will want a fast tack free time. The speed will allow further processing, such as sanding or painting, to occur much sooner. It also helps if the coated component needs to be assembled with other parts. The faster an applicator can post-work their project, the faster their production cycles are. However, a fast tack free time can limit the working window, especially for larger projects.

Note: A long tack free time also creates a great window for recoating and will help with better adhesion. Always check your technical data sheet (TDS) for recoat windows to prevent bad adhesion or additional sanding.

Cure to Handle

Definition: Cure to handle is the time until a material can be handled after application. It usually comes between the tack free time and the recoat window since the material has not completely cured. Most cure to handle times happen minutes after application.

Importance: Cure to handle time directly affects how soon you can handle a coated object after application. It can also tell you how soon it is ready to be sanded, painted, or assembled without compromising the final properties.

It needs sufficient time to cure and develop its properties. If you handle the coated project too early, the surface can crack or become damaged by touch. Handling it too soon can also lead to uneven curing, weak spots and inadequate protection of the underlying surface. Different urethane hard coats will have different cure to handle requirements.

Recoat Window

Definition: The recoat window is a property specific to coatings as it is the time frame between which a previous application can receive a subsequent coat or topcoat. Depending on the coating, a recoat window can extend from minutes to hours and may have different requirements based on the specific formula.

Importance: Some urethane hard coats must be applied in layers to build the thickness. Adding layers is usually done for more adequate protection of the underlying surface. During the recoat time, you can be sure the subsequent coat will have excellent adhesion with the prior one. This property is also important if you must paint over the coated surface for theming purposes. You can be sure that the paint will stick to the hard coat.

If you apply a new coat outside the recoat window, there will be weak adhesion between the coats. That weak bond can compromise the overall integrity of the coating, making it more likely to peel, crack, or delaminate. Poor adhesion can also compromise scratch resistance, impact protection, and other properties. In some cases, the initial coating can be sanded or scuffed to create better mechanical adhesion for the second coat. A strong bond between them will allow them to perform consistently across the entire project.

How to Find Urethane Hard Coat Properties

Because material properties are so important for users to know before they purchase a product, we display them accurately after meticulous testing and review. They can be found on technical data sheets or product pages of any product. Technical data sheets can be found under the resources tab on any product page.

Contact VFI if you would like more information on properties to determine the best product for your project.

Cast Stone vs Manufactured Stone Veneer: Which Should You Use?

You may think the architectural elements you see on commercial and residential buildings are made of real stone, but it is becoming more common for them to be made of concrete. It is hard to tell if an accent wall in a lobby or the columns on a front porch are made of natural stone because man-made products are so realistic.

For years, natural stone was upheld as a premier building material for its beauty and stability. The reason why people are turning to other building materials is due to cost, weight, and sourcing difficulties. Manufactured stone and cast stone were created as solutions to these problems.

What is Natural Stone?

Natural stone is a durable material that is obtained from the earth. It has been used for centuries due to its strength and longevity. To make it an effective building or decorative material, it is cut down, shaped, and finished for an assortment of projects. Though, it is much more difficult to cut than man-made products.

A desirable feature of natural stones is their uniqueness. As a product of nature, no stone will have the exact same pattern, look, texture, or coloring. There is an abundance of natural stone types, including limestone, granite, marble, slate, etc. While each natural stone’s distinct graining and coloring give it character, it prevents uniformity and consistency throughout a project.

What Is Natural Stone Used for?

• Natural stone was once used to create some of the most famous historic structures, monuments, and sculptures around the world, and still is.
• It can be used as decorative architecture on interior or exterior floors and walls. An example could be an accent wall or a fireplace.
• For larger outdoor projects, it can be added to your landscape when designing fishponds, patios, outdoor kitchens, or boundary walls, among other things.
• Natural stone can even be used for furniture like countertops or showers to give your home a makeover. Granite and marble are most favored for these projects as they create elaborate displays that are easy to clean and maintain.

What Is Cast Stone?

Cast stone is a man-made concrete building material whose main purpose is to replicate natural stone at a lower cost. It is used to create complete architectural elements. Cast stone is often mass-produced, meaning you’ll likely find identical pieces across one project, which creates a uniform appearance with consistent quality. Its availability is also not limited by geographical factors, which means it is accessible wherever you are.

It has unmatched design flexibility as it can be molded into various shapes and sizes to achieve your desired aesthetic. It can also be pigmented to match and blend with other building elements. Cast stone can have intricate details, replicating diverse textures, shapes, and patterns without the need of skilled labor carving the shape each time.

Because it’s made of a synthetic material, it often costs less and is lighter than natural stone. As a lighter-weight material, transporting and maneuvering concrete pieces on a site is much easier, especially for larger projects. The manufacturing and installation processes are easier, with less time and labor needed. And even though it is lighter, it is still durable and has high strength as a concrete product.

How Is Cast Stone Made?

Cast stone can either be wet-cast or dry-cast concrete. The wet cast method is commonly used for casting large, structural, and complex elements. A mixture of Portland cement, aggregate, and pigments is combined and poured into molds. The texture of the material will be similar to natural stone and produce finishes that are difficult to distinguish from the original material.

Cast stone can be molded using various materials, including wood, fiberglass, plastic, or rubber. The material you should use depends on the architectural element being replicated and the amount of detail required.

One of the best mold materials is liquid urethane rubber due to its abrasion resistance and tear strength. It handles concrete well without breaking the cast piece and can produce as many as 100 pieces in a single mold with the same consistent detail.

By first casting over an original model, these molds will easily replicate the original piece’s features into the concrete. Due to their flexibility, they are also great for elements with deep undercuts. For most cast stone projects, a 20-30 A material is recommended to obtain desired shapes and details.

What Is Cast Stone Used for?

• It is often used in architectural restoration projects because it is able to replicate and replace the old and deteriorated stone on historical buildings.
• It is popular for decorative elements, trim, ornaments, or facings for buildings and other structures, such as columns, porticos, balusters, pier caps, copings, watertables, window surrounds, door entries, and more.
• It makes great concrete furniture and décor, including tables, benches, plant pots, etc.
• It is found on and in homes, condos, churches, banks, courthouses, and more.

What Is Manufactured Stone?

Manufactured stone veneer is often called a handful of other names, including faux stone, artificial stone, or cultured stone. Like cast stone, it is a man-made material designed to replicate the look of natural stone at a lower price and weight. It differs from cast stone because it is veneer, a thin layer of molded concrete applied to another surface, like wood or flat concrete. It is often used for non-load-bearing decorative detailing, as it does not provide any structural support.

Stone veneer products offer an array of shapes, sizes, and color options that are indistinguishable from natural stone unless closely inspected. As a concrete material, they are strong and durable to be used in indoor and outdoor spaces.

They are not the same thickness and weight that a natural stone would be, making them easier to install in hard-to-reach places. A faux stone can be 15 pounds or less with no support needed when applied to various surfaces.

How Is Manufactured Stone Made?

Manufactured stones are typically pre-cast using wet-pour concrete. Like cast stone, they are made of water, cement, superplasticizers and lightweight aggregate materials. This mixture makes them durable and able to withstand the elements. It is the coloring and molding of the concrete that makes them look like natural stones. When poured into molds with pigment, the concrete mixture is able to resemble marble, granite, limestone, and other desirable stones.

The actual process begins by making a mold. The mold is typically created as the negative of a real stone, so the concrete can mimic the look and texture accurately. When urethane molds are used, the veneer stone will pick up all the details of the stone it is replicating. When making the molds, a 30-50 A urethane material is recommended, as it provides more strength than a lower durometer rubber would.

A small mold of one stone can be made, as well as a large mold with multiple stones that vary in size, which are then packaged together. As a veneer, it is typically cast at about 1 inch thick. Some of the stones will have repeated textures and designs, but that ensures your project will be consistent in quality and appearance.

Manufactured stone veneer will have a flat back for easy installation over a variety of surfaces. While cast stone is typically custom-made, manufactured stones can be laid out and cut to suit the project.

What Is Manufactured Stone Used for?

• The main use of manufactured stone veneer is to create exterior facades and unique statement walls.
• They can be used both indoors and outdoors to elevate the architecture and appearance of office buildings, restaurants, roadways, hotels, medical facilities, etc.
• Due to their flat-back nature, they can be installed over metal, wood, masonry, brick, or poured concrete to add a decorative element to various spaces.
• They are used to elevate the architecture and appearance of various buildings. They can be placed around fireplaces, fire pits, outdoor kitchens, water features, walkways, patios, and more.

If you’re interested in cast stone or manufactured stone, VFI makes a variety of 2 part urethane rubbers that make perfect molds for these projects. Contact us today for assistance in finding the best material.

Urethane Molding and Casting Materials

Industry professionals can greatly benefit from various molding and casting materials when it comes to making structural and architectural concrete elements. Among some of the best materials to use are urethane rubbers.

They are very versatile two-component kits that can be used to make molds, formliners, and stamps for sturdy, functional, and artistic concrete projects. Their versatility comes from the ability to be formulated with varying properties, including a range of Shore hardnesses, which allow the materials to be used for small, detailed projects as well as large structural projects.

What Is a Concrete Mold?

Concrete molds, also called forms, are a type of molding and casting material used to shape fresh, liquid concrete. Once hardened and left to strengthen, these concrete pieces are demolded to be used as building components, decorative elements, or artistic displays.

A concrete mold must be sturdy and abrasion-resistant to ensure it won’t deform during the casting process and the concrete will demold without damage. Molds can be made of various materials, including rubber, plastic, silicone, latex, wood, and metal. Urethane rubbers are among one of the most robust materials for concrete casting. These molding and casting materials can be made into a range of shapes and sizes with various designs and textures. These details are transferred into the wet concrete to influence the final finish of the piece.

The hardness of the mold is an important factor to consider when casting concrete and depends on the piece you intend to produce. The softer the rubber, the easier it will release from a complex, detailed concrete piece. However, softer rubber is not as durable as harder rubber. As urethane’s hardness increases, it is less flexible but more durable. This is why more detailed stone molds (ones with more incuts and the need to compress) use 20-50 A material and large form liners and stamps use 70-90 A material.

How Is It Used to Cast Concrete?

A single urethane mold can be used to make repeated concrete castings that mimic natural materials. It captures high surface detail and can be reused over and over, making it the material of choice for high-volume production. These molds are used to cast concrete in many different ways, including:

• Precast panels – Harder rubber is typically used to make larger structural elements. The concrete material is poured into massive flexible form liners off-site, in a controlled environment. These detailed liners can then make decorative panels, fences, retaining walls, and more.
• Manufactured Stone – Rubber ranging from 30-50 A is great in general assembly lines to make molds for lightweight concrete stone facades and/or decorative exterior elements. Urethane rubber’s dimensional stability is perfect for the repeated casting process required. These stones are used on homes, restaurants, and more.
• Cast Stone – Urethane rubber is made primarily for wet cast stone and is used to create corbels, wall caps, crown molding, and other advanced shapes. Urethane rubber is mainly used in cast stone when compression of the mold is required.
• Hardscape – Rubber stamps or rollers are capable of turning wet concrete into natural-looking, textured pieces that mimic real brick, flagstone, slate, etc., for outdoor decks, patios, walkways, and more. Rather than using expensive natural stone, stamping concrete with urethane can create pavers, steppingstones, small retaining walls, and curb walls for less.
• Décor & furniture – Concrete can be cast into molds to make large statues or art pieces for decoration or even functional elements like benches, countertops, planters, fireplaces, and outdoor kitchens. These creations can utilize stone veneer as a finish or cast stone for complete pieces.
• Architectural Restoration – Softer urethane rubbers are great for restoring old stonework on buildings. The lower durometer makes it easier to demold around complex shapes and undercuts without damaging the original piece.
  Whatever your project is, it is important to use an appropriate mold release when casting concrete. While urethane is an extremely durable material, it can also create strong bonds with many surfaces.

Not using release can have disastrous effects on the mold and concrete pieces. Even with a release, you may have to use a tool to pry the piece out of the mold if it’s stubborn. VFI, however, has developed new easy-releasing urethane rubbers for ease of use and reduced breakage when used with release.

Are there Alternatives to Urethane?

Choosing the right material is essential to ensure it will meet the needs of your project. And while urethane does come with great benefits, there are alternatives that might be better for your application. Other materials must be non-porous, non-reactive with concrete, and rigid enough that the mold won’t change shape once the concrete is cast.

1. Silicone rubber molds

Silicone is another flexible molding and casting material that produces intricate designs and textures on concrete elements. It has outstanding demolding characteristics that don’t require mold release. It works well for architectural restoration since it is able to keep the original model intact without damaging it.

However, polyurethane has more variety when it comes to hardness so it can be used in a variety of concrete applications that silicone may not be able to. Silicone is also more expensive and not great for large-scale, high-volume concrete casting. Shrinkage is another major concern with silicone when repeatedly casting concrete.

2. Plastic forms

If you desire a more affordable material, various plastics like ABS have been used to cast concrete for decorative and artistic pieces. They can offer high detail in the cast part, producing complex shapes and fine textures. They are also relatively easy to use due to their lightweight nature. However, making these molds requires certain skills and techniques you don’t need with urethane. Most plastic molds will need to be purchased from a manufacturer and will have a preset design. They also will not last as long as other materials, producing only about 10 castings per mold.

3. Wood forms

Wood molds can be custom-made and are easy to construct for large-scale structural elements. They are versatile, tough, and strong, and because wood is readily available, they can be more affordable for certain projects. However, these molds are not as durable as other materials and are not suitable if you want intricate designs or curves in the concrete. To increase the usability of these forms, a form coat epoxy can be used to protect the casting surface from abrasion.

4. Metal forms

Most metal molds are made from either steel or aluminum and can be used for structural or decorative concrete purposes. They are durable, made to last, and, like wood, produce smoother finishes. Similar to making plastic molds, metalworking requires specialized tooling and skills for precision. Metal is ideal for repeated, high-volume use when making concrete pieces for larger industrial projects that require strength and durability over aesthetics. Most metal molds will be small because of cost restrictions. A form coating epoxy can be used for long-term protection of these forms as well.

5. Latex molds

Because of its low viscosity, latex is applied to a model by brushing on multiple thin layers until the desired thickness is met. Having to apply multiple layers is a big drawback to using this material. Some latex molds can take as long as 2 weeks to finish because they don’t cure as quickly as silicone or polyurethane. So, if you require quick production, this is probably not the material you want to use. Also, due to latex being used as a thin film, you will always need a rigid backer mold for casting. However, it is probably the strongest and most resilient material, leaving you with long-lasting molds for years.

Why is Polyurethane Rubber Better?

• It is a long-lasting, reusable molding and casting material. Due to its high abrasion resistance and strength, it is more durable than other materials.
• It creates highly detailed and accurate concrete pieces that mimic natural materials. With high flexibility, the material is able to form around complex undercuts and other details to make perfect copies of the original.
• It is easy to work with. While it requires a release agent for demolding, it requires little effort to separate it from delicate details once the concrete has set. There are also easy-releasing urethanes available at VFI, which makes using these materials more desirable when heavy release cannot be used.
• It can be a cost-effective option compared to silicone and metal molds. Silicone has a few benefits that urethane lacks, but they’re fairly equal in their abilities. While it is more expensive than wood or plastic, it makes up for that cost in its longevity, flexibility, and reusability.
• It is an extremely versatile material that can come in a range of hardnesses to complete both large and small projects. There’s really no limit to what urethane molds can be used to create.

VFI manufactures a variety of urethane rubbers for various concrete casting projects. Contact us today if you need help finding the best material for you.

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