How to Use Liquid Foam to Make a Mold


Liquid foam sprays are made of polyurethane rubber. Two chemicals combine to produce spray foam that easily coats both large and small surface areas. Using a foam spray also makes it possible to cast items vertically, by not having to remove them from walls. This is great for matching detailed plaster work on ceilings, walls and crown molding pieces. Spray-foam polyurethane rubber is suitable for casting a variety of materials including wax, gypsum and concrete.

Things You'll Need

  • Spray foam applicator
  • Spray foam cartridges
  • Paint brush
  • Putty knife
  • Spray foam plastic coating cartridge
  • Attach tube to the center of the spray foam cartridge set and secure with the plastic washer. Attach spray nozzle to the end of the plastic tube and insert entire cartridge into the foam spray gun. Connect the spray gun tubing to the cartridge nozzle and adjust spray flow with the dial on the nozzle.

  • Coat the object to be molded with the spray foam rubber. Coat the entire piece with enough foam to cover the object completely, about 1/2 to 1 inch thick. Use a paint brush and putty knife to fill in or smooth over any holes or gaps in the coating. This is especially important if the object is on a wall or part of a wall.

  • Let the spray foam rubber cure for at least 1 hour or up to overnight.

  • Clean the applicator and all tubing with warm water.

  • Insert the spray foam plastic coating cartridge into the clean applicator and reconnect all tubes and hoses according to the directions in step 1.

  • Apply the plastic support shell to the foam rubber with the spray applicator. Spray the plastic until the foam rubber is completely covered and no blue foam rubber color is showing through. Pay particular attention to deep grooves and crevices in the object.

  • Let the plastic outer coating cure for at least 1 hour or up to overnight and remove the mold from the object. The mold is now ready to use for casting.

Tips & Warnings

  • Stick a few strips of wood to the object while the plastic outer shell is wet. These will allow you to remove the rubber mold easily. Use as many or few as you need depending on the size and position of the mold.
  • Always use an approved face mask or aerator and protective eye wear when working with any spray product.

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