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Painting aluminum, for the do-it-yourself boat owner, is often a matter of maintaining a pre-existing finish. Painting a new, unpainted aluminum boat, like any other paint job, may seem like it's more about the surface preparation -- degreasing and sanding so the primer coat will stick to the metal and applying the primer immediately to prevent the aluminum's oxidation. The paint is more than a decorative afterthought, however.
Latex (Water-based) Paints
Here's something to think about: latex paints last for 10 years or more in rain, snow and sunlight. The simple explanation is that the water base makes it easy for you to spread the colored chemicals -- the paint's tint -- onto the surface of your boat. When the water evaporates as the paint dries, the molecules of the tint have bonded chemically to the primer you applied. Latex paints offer the same simplicity of application to the aluminum-boat owner as they do the home owner since you can apply them by brush or roller or, if thinned properly with water, by spraying them onto an aluminum boat with an airless sprayer.
Alkyd paints are synthetic, oil-base paints with a very high degree of water-resistance. They require little maintenance once applied. Like latex paints, they may be applied with brush or roller but, if applied with a paint sprayer, they must be thinned with petroleum distillates like naptha, xylol or other mineral spirits. These present issues of flammability, storage and environmental hazard. In spite of this, alkyd-based paints are a suitable coating for your aluminum boat.
Epoxy paints, or two-part paints, are made up of a polymer resin and a polymer hardener. When the two parts are mixed, they begin to cure; when the curing process is complete, they form a durable surface coating. As with alkyd paints, they may be brushed, rolled or sprayed onto your aluminum boat. Like alkyd paints, they must be thinned with specialized thinners before spraying. Because of differences in manufacturer formulas, read the instruction label on your paint carefully for thinning recommendations.
Zinc chromate is described by the Federal Standard 595 Color Server as "an anti-corrosive barrier primer" and "a sort of painted-on galvanizing." It comes in various colors, primarily green or yellow. While the trade names may vary, if you ask for zinc chromate primer at a retail paint store, you'll have no trouble finding it.
Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.