Why Is My Hard Coat Cracking?

Hard coats are supposed to be durable protection over surfaces like EPS foam for theming, so why are customers experiencing cracking? Cracking is a stress-related failure, which stems from substrate movement, lack of flexibility, extreme temperatures, and improper application.

Reasons Hard Coats Crack

Reason #1: Substrate Issues

Using the incorrect substrate for a hard coat can cause future issues. A general rule of thumb is you cannot apply a rigid coating to a surface that is softer or more flexible than the coating.

Hard coats are high on the Shore hardness scale. VFI’s hard coats are 65-75 D, which makes them feel very plastic-like, similar to a hard hat. Since these coatings have higher hardness properties that limit their flexibility.

Certain surfaces are more flexible and will expand and contract in extreme environments. Because the coating is rigid, it won’t be able to bend and flex with a surface that is more flexible than itself. This lack of flexibility makes them more susceptible to cracking from substrate movement.

Reason #2: Environmental Factors

Your hard coat’s ability to handle stress is closely associated with the environment. If your theming project is exposed to extreme temperatures, sunlight, humidity, and impact, it will degrade eventually.

Hard coats traditionally do not handle thermocycling or weathering very well. Our hard coats have a heat deflection temperature of 107°F, which means they will start to distort under stress at that temperature. This is a reason they need to be supported by a surface. The good thing about using EPS foam underneath is that the coating will hold strong unless the foam fails.

However, if you are installing the project in a location like Las Vegas where temperatures are high year-round, expect cracking to occur over time on dark surfaces. While substrates like EPS foam have good thermal stability, once they reach above 170°F they will start to fail. The failure of the substrate is what causes the coating to also fail and crack.

Reason #3: Improper Application

Coatings can fail if they aren’t applied correctly. If the surface is dirty or contains contaminants before the coating is applied, it can affect adhesion. If the coating is not properly adhered to the surface, it can delaminate, peel, or crack.

Applying the coating outside the recommended thickness range can also cause issues. If the coating is applied too thick or too thin, it has a greater chance of cracking. It will be very brittle unless it reaches a certain thickness.

Solutions

No one wants their hard coat to crack. These failures lead to extra costs, material waste, and project delays. The best way to prevent cracks is to use the right coating system and substrate for your environment.

If temperatures get above 170°F, a hard coat over EPS foam is not the recommended material. For a hard-coated project to last as long as possible, it should be placed in a relatively temperature-stable environment.

There is an alternative to using a hard coat. You can use a softer, more flexible coating. Softer coatings provide the needed flexibility to accommodate stresses and impacts without affecting the underlying surface. You may also need to use a different substrate.

VFI offers several products that will work for various application needs. VFI-3119 70 A Polyurea Hybrid Spray Coating or VFI-3131 65 A Polyurea Hybrid Spray Coating are softer coatings that can be applied to flexible surfaces like flexible foam. They offer great resistance to thermocycling and outstanding durability in diverse climates.

We’ve also seen theming fabricators use other substrates to create more durable structures. EPS foam is only going to get you so far with its thermal stability. If you created your structure from a material like metal or wood, it would have better thermal and structural stability.

VFI typically recommends a polyurea hybrid coating like our VFI-542 High Pressure Spray Bedliner for metal surfaces. It’s a cost-effective material in comparison to some polyurea and polyurethane coatings on the market. At 40-50 Shore D, our bedliners have more of a rubber-like feeling. They also have the ability to withstand cracking, warping, and peeling in extreme hot and cold temperatures.

A few other tips to remember to prevent cracking include:

• Ensuring proper surface preparation and application of your coating.
• Following the manufacturer’s instructions listed on the technical data sheet.
• Remember that if you apply paint as a topcoat, it has to be more flexible than the coating beneath it, otherwise it will crack.

Contact VFI if you need assistance finding the right hard coat material for your specific theming project. We also have recommendations for what you should and should not use to repair hard coat cracks.