Painting fiberglass and gel coat take different techniques.
Fiberglass gel coat is not an ideal surface for paint. It is so slick and has such low porosity that paint has a hard time adhering. A primer coat that chemically softens the gel coat and bonds to it should be used prior to applying the first finish coat of paint. Special fiberglass primers are made just for this purpose.
According to International Paint (Interlux), the use of this type of primer results in better adhesion of the finish coat than can be obtained by sanding the gel coat with 80-grit paper. Always choose a primer that is compatible with the finish coat paint. If sanding is chosen instead of a primer coat, the goal should be to remove all gloss and establish a good anchor pattern for the paint.
Primer can be applied with a brush or a roller. Using a roller speeds up the work and provides a more even film thickness.Do not worry too much about looks at this point. Just be sure that the entire surface is given a thin even coat with no skips. To understand how a fiberglass primer works, think of flypaper that is sticky on both sides. The primer softens and bonds to the gel coat on one side. On the other, it provides a chemically compatible base for the first coat of finish paint. Professionals often refer to this type of primer as a "tie coat". The chemical bonding to the finish paint works best when the primer is still quite fresh.
Apply two coats of epoxy primer, sanding in between coats. The next step is to sand the entire surface with 220-grit sandpaper, depending on the hardness of the surface. When power sanding, a variable-speed random orbital sander with a circular foam pad works best. Hold the sander perfectly flush on the surface or you will create dips and swirl marks. Avoid the temptation of tilting the sander from the flat position when sanding areas where filler was used.
When hand sanding, always use a sanding block (rigid or foam) to ensure that you do not add any dips in the surface that may appear in the finished surface.The next day wet sand the entire area with 220-grit paper and lots of water. Then do a thorough water wash and a full wipe down with thinner, rotating and throwing out the rags every couple of feet. Then paint it again. Be sure not to touch the surface after cleaning or you will spread contaminants that can affect the cure.
Products that could be used are:
- Interlux Pre-Kote Primer
- West System 800 Foam Roller Cover
- West Marine has 1/8" nap foam roller with a phenolic core>/li>