Surface preparation is the key to achieving a beautiful paint job. The topside paint system you choose will dictate what type of surface prep is needed. Most marine topside paints are either one-part, air-dry products or two-part activated products. Make sure you apply the recommended primer for the paint system you choose.
Surface prep for most one-part topside marine paints requires that you sand the surface with 180-320 grit sandpaper so the paint can achieve the strongest mechanical bond, and a smooth finish. After sanding, wipe the surface with a clean, lint-free cotton rag dampened with the recommended solvent to remove contaminants such as wax, grease, water, oil, dust, dirt, sanding residue, or any other foreign matter which can have a negative effect on the finish and the cure. Change out your rag, as needed, then follow with a clean, dry lint-free cotton rag to remove any remaining residue.
Surface preparation for two-part paints usually involves fairing the surface smooth before priming and painting. Two-part paint systems usually require priming with an epoxy-based primer to form an inert, solvent-resistant surface on which to to apply the paint. The solvents in epoxy primers and two-part paint systems are stronger than in one-part primers and paints, so it's critical to use proper personal protective equipment. Each primer and paint system will have its own list of solvents to use for surface prep, cleanup and application. Don't substitute any of the required solvents because they're created to work with each step in the priming and painting process. Always use clean, lint-free cotton rags when doing solvent wipes, and always follow a solvent-dampened rag with a clean, dry rag. Failure to use a cotton rag for solvent wipes may lead to a coating failure because wo-part paint systems are much more sensitive to contaminants, including grease, wax, oil, dust, water or moisture, sanding residue, or any other foreign substances. Signs of contaminants can include bubbling, blisters, fish eye effects, peeling, areas of improper cure, or spots with an inconsistent appearance. Prime the substrate as directed, allow the primer to cure, and sand the primer smooth. In general, two-part paints create a much stronger bond than 1-part paints, so the surface can generally be sanded with a finer sandpaper than that used for one-part paints. Use the specified solvent-wipe solvent to wipe the surface carefully, and follow with a clean rag wipe before applying paint.
Always use proper personal protective equipment (PPE) for any sanding, solvent wiping, or painting.