How to Use a Form Coat Epoxy

Learning how to use a form coat epoxy is important for generating multiple quality castings when using abrasive casting materials. Creating a stable surface to pour concrete will help control and shape it as it cures. These qualities help ensure that the material will set properly and maintain its strength, durability, and longevity when transported and installed at building sites.

However, bare wood, foam, and metal surfaces will not last long without a form coating, so it’s crucial to protect your investment with a strong barrier. Using an appropriate coating will ensure that the surface can withstand the weight of rough casting materials for multiple uses without becoming damaged.

What Is a Form Coat Epoxy?

Form coat epoxies are also called mold coats or bed coats in the precast industry. This is due to their versatility, as they are used to protect large formwork, casting beds, or molds for precast, tilt-up, slip form, and cast-in-place applications. The castings produced from these forms include beams, columns, walls, etc., made of cementitious materials.

A form coating creates a tough, rigid surface that adheres well to wood, steel, and even EPS foam. It acts as a barrier to protect these expensive molding forms from the abrasive effects of various casting materials. The coating will act as a shell over the surface to prevent it from absorbing the casting material, which would otherwise have a hard time releasing from the form or surface. The smooth coated surface is then used to create multiple identical and flat building materials for parking structures, bridges, highway walls, retail shopping centers, and more.

Specially formulated epoxy coatings work well for this application. They are rigid but are formulated to also have the flexibility to resist cracking or deforming from regular use. Because these coatings have outstanding properties that make them strong, they become almost unbreakable, reducing the risk of damage to the underlying surface. Epoxy coatings require minimal maintenance and will endure heavy wear and tear before they need to be recoated.

Importance of Surface Preparation

For excellent adhesion to the following surfaces, you must ensure they are free of dirt, debris, and other foreign materials.

  • Wood forms – Sand new wood panels for good mechanical adhesion of the coating. Clean off the sawdust with a vacuum. Though the coating is moisture insensitive, ensure the surface is relatively dry before application.
  • Steel forms – If the metal contains rust, mill scale, dirt, and other contaminants, you will want to conduct abrasive blast preparation by sandblasting to SP6. Once finished, clean the metal shavings off the surface with a vacuum or broom.
  • EPS forms – While EPS is typically not used for large-scale production, it can be used for casting smaller pieces. The foam must be aged at least 30 days to allow any gas to escape. The higher the density of the foam, the nicer the finish, but any foam between 1-3 PCF is acceptable. The foam should be clean and dry before applying the coating. The coating will not deform the mold shape.

The Form Coating Epoxy Application Process

Materials needed: VFI-4385 82 D Form Coating Epoxy, nap roller, wet film thickness mil gauge, large industrial orbital or rotary sander

Because epoxy can be toxic when inhaled, swallowed, or in contact with skin, use the material in a well-ventilated area. Wear the necessary personal protective equipment (PPE) to avoid exposure.

It is always recommended to work with the material at temperatures between 60-80°F. Remember, you will have a shorter working time when the temperature is higher. After preparing your casting surface, follow the steps below to create a protective barrier on your molding surfaces.

  • Once you have mixed the components together, pour the material onto the surface.
    • Note: Leaving it in a mixing container can cause it to over-generate heat, which causes the material to thicken faster and cure faster. Do not leave material in a mass to cure. Mix up only what is needed to prevent excess.
  • Begin rolling the material evenly at a rate of about 20 mil passes. It can be back-rolled to help achieve a uniform thickness. Coverage will vary in the first application due to the porosity of the surface.
  • Check the thickness with a wet film thickness mil gauge. The coating should self-level.
  • Allow it to cure overnight (minimum of 16 hours).
  • Once cured, power sand the surface to smooth out imperfections or bubbles. Clean the surface of dust and debris from sanding.
  • Apply a second coat following the same instructions. Repeat the process until the overall desired thickness is achieved.
    • Note: Total thickness should not be thicker than 250 mils.
  • Before casting, spray a release agent to prevent unwanted adhesion between the form coat and casting material.
  • Pour the casting material into the coated form and allow it to harden until it can be removed, typically after 24 hours. The surface can then be reused for future castings if the surface is clean, free of dust, and dry.

Once the original form coat becomes worn, a new coat can be applied. All you need to do is sand down the existing coating to remove any previous casting residue and improve surface adhesion for the new coat.

VFI Compatible Products

VFI-4385 82 D Form Coating Epoxy is VFI’s exclusive product for precast manufacturing purposes. It has a convenient 2A:1B by volume mix ratio for easy application with a roller. It is moisture-insensitive, so it can be applied to damp surfaces with no effect. At 82 D Shore hardness, the cured coating will produce a highly rigid yet flexible surface perfect for repeated concrete casting. Contact VFI if you are interested in protecting your wood, steel, or foam surfaces.