Release film

Release film is a plastic film used to cover gelcoat or epoxy while it cures.

There are several reasons for using a release film

• masking an area to protect it from adjacent resin or epoxy repairs.
• covering the surface to make it smooth.
• protect unwaxed gelcoat from air while it cures.

Release films can be made of any low-surface-energy plastic. These include polypropylene, polyethylene, polytetrafluoroethylene (PTFE - e.g Teflon) and others. Household wrap - Saran Wrap is one brand name will also work. The best release films are relatively thick. Household wrap tends to be so thin that it wrinkles easily and results in a poor surface finish.

Some manufacturers of gelcoat repair kits use Mylar film (polyester) as a release film. You have to be careful with Mylar - in its "pure" form, it is a high-surface-energy plastic. There are many different versions of Mylar. Some are coated with surface treatments to enhance adhesion. Others are treated for reduced adhesion. The latter are suitable for use as a release film. However, if you buy Mylar at, say, an art store, there is no way of knowing what the surface energy will be like. Unless the Mylar is specifically sold as a release film, it is best not to use it or test before using it with an adhesive.

Plastics such as polyester (including polyethylene terephthalate or PET), polycarbonate, polystyrene, ABS and many others are unsuitable for use as a release film. If in doubt, do a good test before committing to real work.

For covering unwaxed gelcoat, you can also paint on a layer of polyvinyl alcohol (PVA). It will dry and protect the gelcoat from air as it cures. However, it will not provide the advantages of a smooth surface that a film will.