PVA (poly vinyl alcohol) is a liquid release agent that creates a thin film over the surface. This film is very strong and resistant to many chemicals, including epoxy and polyester. This makes PVA suitable for use with damaged molds, molds with a poor surface, on surfaces with an unknown or unsuitable composition, such as porous or sanded surfaces, or surfaces that are not resistant to polyester.
The application of polyvinyl alcohol is easy with a brush or a damp sponge. Make sure that the entire surface is covered with polyvinyl alcohol. PVA can also be applied with an spray system. You can dilute the PVA loose lacquer with water or alcohol. Spray a mist coat first, then a wet coat.
After application, the PVA will dry to a tough film in about 1 hour. After drying, you can apply your gelcoat, polyester or epoxy product in the mold.
Apply the PVA in several layers on porous surfaces until it has formed a dense film on the surface.
Release is easy: you add some lukewarm water and this will cause the Polyvinyl alcohol to dissolve low. The final product and mold can also be cleaned with water.