Unlike wood, fiberglass surfaces are nonporous, making them unsuitable for spray paint adhesion. Before you can spray paint any type of fiberglass surface, you will need to employ specific preparation techniques to condition the fiberglass to accept paint, or the finish will peel soon after application. In addition, because fiberglass is slick and smooth, you will need to use a particular application technique to promote a smooth, professional-looking finish free of runs, drips, and sagging.
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Clean the fiberglass using dish soap. Rinse the surface, and allow it to dry completely before continuing.
Abrade the fiberglass to promote adhesion by sanding it with a palm sander loaded with 400-grit sandpaper.
Wipe down the fiberglass with a tack cloth.
Cover any areas of the fiberglass you do not want painted with painter's tape. Cover large areas below or adjacent to the fiberglass with drop cloths.
Apply a very light coat of primer to the fiberglass. Spray in intermittent mists to promote a professional-looking finish free of runs, drips, and sagging. Do not apply a constant stream, or you may end up with flaws in the finish coat.
Allow the primer to dry and cure for fours hours, and then apply a coat of acrylic spray paint in the same way you applied the primer.