Choosing the right type of paint for fiberglass parts will help your part last longer, and look better for the length of time it is in use. It can also add additional qualities like glosses, matte finishes and shines that can make your new part match your old parts, or give whatever it is you are building the look you want.
Assess the fiberglass part you are making. How big is it and what is your budget for paint? Many paints will be fairly expensive, so be prepared to spend a lot to protect your new project.
Decide what type of finish you want your object to have. Fiberglass paints are available in high gloss, gloss, matte and flat finishes. In addition, you might find flake metal paints that can add additional texture and a unique flashy look.
Decide what kind of protection you need from water and sunlight. Both can cause damage to fiberglass over time, because fiberglass is susceptible to incursion by water and sunlight causes resins to break down. Once you decide this, you can start to narrow down your choices. Many gel coats, which are basically fiberglass-like gels with pigments in them, do not hold up well to sunlight. Other paints provide thicker coats and more protection against nicks and scratches.
Pick a paint based on the type of fiberglass you used. If you use an epoxy resin fiberglass, consider using an epoxy-based paint. Interlux makes a good epoxy-based paint for marine uses. If you are using a polyester-based resin, a polyester-based paint is a good choice. Both will adhere better to the surface because their compounds are similar.
Determine whether you want to use a self-drying or catalyst drying fiberglass paint. Catalyst drying paints must be mixed with a drier in order to dry. The advantage is you can speed up the drying time by adding more compound and drying the part at a higher temperature. The disadvantage is the additional mixing involved.
Assess the surface of the part. If it has small grooves or pits, a self-leveling fiberglass paint is a good choice. These paints will actually seek out pits and fill them first, creating the smoothest possible surface.
