The saying that "a paint job is only as good as the preparation" is one of the most important things to consider before starting a new paint job. The first step is to select a paint system. This will dictate how to prepare the surface properly. Choosing a paint system is a compromise of cost, the painter's ability and skills, application method, color options, environmental conditions, as well as the longevity and durability of the paint. Most marine topside paints can be broken off into 1-part air-dry products and 2-part activated paints.
Surface preparation for 1-Part Paints
One-part paints cure on their own without the requirement of any other components. They are generally more forgiving than 2-part paints, they are more cost effective, but they are not as hard, durable, abrasion resistant, or solvent resistant. One-part paints also do not have as long of a useful life. Always use proper personal protective equipment (PPE) for any sanding, solvent wiping, or painting.
The substrate should be fair and smooth before any primer or paint is applied because the primer and paint will directly reflect the smoothness, or the texture of the surface beneath. One-part paints can generally be applied over 1-part primers, or in many cases, directly applied to fiberglass, wood, and in some cases, metal. Epoxy-based 2-part primers can also be used before applying 1-part paints, but may be deemed excessive, due to the cost, strict mix ratio, and stronger solvents needed to prepare the surface for the epoxy primer.
Most 1-part marine paints require the surface to be sanded smooth with 180-320 grit sandpaper for the paint to have the best mechanical bond possible, with a smooth finish. After sanding the substrate smooth, the surface should be wiped with a solvent to help remove any contaminants. Grease, wax, oil, water, dust, dirt, sanding residue, or any other foreign substances can all be considered contaminants, which can have negative effects on the cure, or finish, of the paint being applied. Generally, less aggressive solvents can be used for removing sanding residue and cleaning the surface before painting. Always use a clean, lint-free cotton rag with any solvent wipes because some solvents can break down synthetic rag materials, leaving a residue. Only use the recommended solvents with 1-part primers or paints because using harsher solvents or incompatible ones can cause damage to the substrate, or prevent the paint from applying or curing properly. Dampen a rag with the solvent, and wipe the surface clean, changing out rags, as needed. Then follow with a dry, clean, lint-free cotton rag to collect any remaining contaminants that are sitting on the surface. Apply the paint as directed, when all environmental conditions allow, for a thorough dry time.
When applying a 1-part paint to a previously painted surface, the substrate must be in good condition, with no signs of peeling, bubbling, or other paint failure. Dewax the substrate, removing any grease, wax or oils first, using an appropriate solvent, and sand the surface according to the paint's surface preparation instructions. Wipe the surface, as directed above, with the specified solvent wipe, and apply the paint as directed, when all environmental conditions allow, for a thorough dry time.
Surface preparation for 2-part paints
Two-part paints are far more sensitive in their surface preparation needs. As with 1-part paints, the surface needs to be faired and smooth prior to priming and painting. These paint systems usually require an epoxy-based primer to form an inert, highly solvent-resistant surface to apply the paint to. Some primer systems can be designed for high-build for minor fairing, and others are designed for thin, fine application, as a tie-coat for the paint. The solvents in epoxy primers and 2-part paint systems are much stronger than with 1-part paints and primers, making it more vital to use proper PPE.
Each primer and paint system usually has its own list of solvents to use for preparation, cleanup, and application. Do not substitute any of the specified solvents, as they have been specifically blended to work with each step in the priming and painting process. Always use clean, lint-free cotton rags when performing any solvent wipes, and always follow a solvent-dampened wipe with a dry rag. Failure to use a cotton rag for solvent wipes may lead to a coating failure.
Two-part paint systems are far more sensitive to contaminants, including grease, wax, oil, dust, water or moisture, sanding residue, or any other foreign materials or substances. Symptoms of contaminants can include bubbling, peeling, blisters, fish eye effects, spots of improper cure, or spots of an inconsistent appearance. The stronger solvents used can break down synthetic rag materials, leaving a residue of contamination behind. Two-part paints and primers are much more sensitive to any sorts of contaminants, so extreme care must be taken. Prime the substrate as directed, allow the primer to cure, and sand the primer smooth. In general, 2-part paints create a much stronger bond than 1-part paints, so the surface can generally be sanded with a finer sandpaper than that of 1-part paints. Wipe the surface clean with extreme care, using the directed solvent-wipe solvent, and follow with a clean rag prior to applying any paint. Only apply 2-part paints when the environmental conditions allow, for proper cure.
When applying a 2-part paint to a previously painted surface, it is imperative to make sure you're applying it to a previous 2-part paint or primer. The solvents in 2-part paint systems can soften or destroy most 1-part paints, resulting in an inevitable coating failure. Remove any coatings that are bubbling, peeling, otherwise failing, or showing signs of poor adhesion. For substrates in good condition, use the directed solvent wipe to remove any surface waxes, greases, oils, or other surface contaminants prior to sanding the surface. Sand the surface as directed by the paint manufacturer. Remove any sanding residue and wipe the surface clean with extreme care, using the directed solvent-wipe solvent, and follow with a clean rag prior to applying any paint. Only apply 2-part paints when the environmental conditions allow, for proper cure.