The Saltwater Magazine for Gulf Coast Fishing!
Below-the-Waterline Painting
by Cam Metz
Antifouling paint protects a boat's bottom from the attachment of fouling organisms, such as barnacles, encrusting zebra mussels and algae. Most antifoulings release copper compounds into the water by leaching or ablative methods. Leaching antifoulings release (leach) copper into the water, dissolving only part of the paint film. The film left behind eventually prevents further leaching and must be sanded off or pressure washed before repainting. With ablative antifoulings, controlled erosion (ablation) of the paint film weakens paint resin and the depleted film polishes off in the water. Ablation results in a continuously renewed surface, with fresh toxicant always available and much less sanding required before repainting.
Once the type of antifouling paint is chosen, then, depending on the type of hull, different steps are required for painting. Here are some general guidelines to follow.
Bare fiberglass hulls: Choose from sanding, no sand or gelcoat blister prevention systems.
For the sanding system, dewax using a fiberglass dewaxer and sand thoroughly with 80 grit production paper. Next rewash with a dewaxer, and apply two coats of antifouling paint.
For the no sand system, first dewax. Next, following the label instructions exactly, apply a thin coat of primer. When primer is slightly tacky, apply two coats of antifouling paint. The drying condition of the primer is somewhat different for ablative paints, so be sure to read the label carefully before using this system.
To use the gelcoat blister prevention system, first dewax thoroughly.Second, sand with 80 grit production paper and rewash with dewaxer. Third, apply multiple coats of an epoxy primer, until a minimum dry film thickness of 18 mils. is achieved, followed by two coats of antifouling paint.
Bare wood hulls: Sand thoroughly with 80 grit production paper, and wipe clean with a tack rag dampened with thinner. Then apply the first coat of antifouling paint, thinned 25% by volume. Last, apply two coats of antifouling paint at full strength.
Bare steel hulls: Sandblast and non-sandblast systems can be used. For the sandblast system, first sandblast to near-white metal (SSPC SP-10 or equivalent), and remove blasting residue with clean compressed air or a clean brush. Next apply multiple coats of epoxy primer until a total dry film thickness of 18 mils. minimum is achieved. Then apply two coats of antifouling paint.
To use the non-sandblast system, first hand-tool clean the hull, eliminating all loose rust, millscale and other foreign contaminants, and remove residue with clean compressed air or a clean brush. Next apply one coat of steel primer, drying until slightly tacky, and apply multiple coats of epoxy primer until a total dry film thickness of 18 mils. minimum is achieved. Last, apply two coats of antifouling paint.
From Kop-Coat Marine Group, 36 Pine St., Rockaway, NJ 07866.Phone: 800-221-4466.
Editor's note: Cam Metz is vice president and general manager of Kop-Coat Marine Group, which produces a broad range of marine paints and coatings.