Boat Painting FAQ

Of all the questions boatowners ask the experts at Interlux, these 8 are the most common.

Q: How should I choose an antifouling for my boat?

A: Besides selecting bottom paint for the type of water where you boat, whether freshwater, saltwater or brackish, the most important consideration is how often you use your boat. You don’t need any coating on the boat’s bottom if it’s moved constantly. If used once a week, then apply an ablative paint, such as Micron CSC or Micron Extra. Every outing generates a fresh coat of copper, renewing the antifouling properties. Boats that are used more frequently require a hard paint that leeches out, such as Ultra-Kote, rather than wears off. Two or three coats of a hard paint can last up to 18 months no matter how far or how fast you travel.

Q: Does my new fiberglass boat require application of a barrier coat below the waterline?

A: A new boat has a very dry hull After launching, the boat’s bottom immediately starts to soak up water. Though most boatbuilders offer a limited hull warranty, it’s usually prorated over a few years. If you’re planning to keep your boat, it’s worth the expense of a barrier coat. Besides the maintenance factor, you’ll get better return on your investment when selling the boat.

Q: Is it necessary to sand after priming?

A: Some manufacturers offer a no-sand primer, but to minimize any chance of flaking, it’s best to sand the primer before application of antifouling.

Q: How do I prep a hull that has never been painted?

A: You must remove the thin film of mold release wax on the surface, then sand it before applying bottom paint. Wash the hull thoroughly using a Fiberglass Solvent Wash 202 and agitate the surface with a Scotch-Brite pad. Rinse the hull with water, which should sheet off. Where the water beads, you’ll need to repeat the solvent wash and scrub. Continue flushing the hull with water until all wax is removed. Now sand with 80 to 120 grit paper. Hull cleaning is important. Sanding heats any remaining wax on the surface, and then pushes it into the open pores in the gelcoat. That will keep any bottom coating you apply for the first few years from sticking.

Q: I’ve purchased a boat used in freshwater that has Interlux VC 17m on the bottom and plan to launch it in saltwater. How do I prep the bottom?

A: VC 17m is a very thin film. Either strip with B172, an alcohol-based stripper, or denatured alcohol, or overpaint with a compatible paint, such as ACT. To strip, lightly wet sand with 80-grit paper to open up the pores, soak a Scotch-Brite pad with stripper, and scrub.

Q: Are VC 17M or VC Offshore available with Biolux?

A: Apparently these products are in the works but they are stalled in the registration process.

Q: Should I use VC Tar or Interprotect as a barrier coat under VC 17m?

A: Four or five coats of VC TAR comprise the conventional undercoat for VC 17m, as it remains more flexible then an epoxy system. Nowadays, more and more boat owners are using Interprotect 2000E/2001E. Applying five or six coats, sanding the final coat with 320-grit paper, gives a harder and slicker bottom.

Q: How do I get paint to adhere to my propeller, shaft and strut?

A: Painting underwater metals is a four-step process: degrease, etch, prime, then paint. Clean the surface with Fiberglass Solvent Wash 202 or its equivalent. Now etch the metal using an etching solution, such as Viny-Lux Primewash 353/354. Etching provides the chemical and physical bond for the primer. Without etching, the primer and paint will flake off in sheets. Cover with an underwater metal primer, such as Interlux 360R, or epoxy barrier coat. Priming also isolates the different metals. These two steps should last five to 10 years when properly prepped and primed. Apply a copper-based hard paint, such as Fiberglass Bottomkote, rather than an ablative paint. Outdrives require a bottom paint specially formulated for aluminum, such as Trilux.