To ensure the best possible bond and the most effective antifouling results, take time to assess the type and amount of surface preparation needed. Typically, most ablative bottom paints can be applied over hard paints, but not the other way around. Also most other antifouling paints can’t be painted over vinyl or Teflon bottom paints. Incompatible paints must be removed first. Substrate matters, too, so for example, if you’re painting on steel or aluminum, check that you coat the surface with an appropriate metal primer first. Incompatible bottom paint or previous bottom paint that is extremely deteriorated should be stripped first. Use a chemical stripper that works with bottom paint to remove it.
If you stripped the old antifouling and found hull damage or damage to the barrier coat, or if you’re painting a new boat for the first time, you’ll need to apply an epoxy barrier coat before applying bottom paint.
Cleaning Tips
In many cases, you’ll be painting over a previous bottom paint job that’s in good condition, so you don’t need to strip the paint or sand. Just chip away any loose paint with a paint scraper or putty knife, then abrade with a medium-grade 3M Scotch-Brite pad, then wipe the surface with a clean, lint-free cheesecloth, rag, or tack cloth dampened with acetone or mineral spirits (or thinner recommended by the paint manufacturer) to remove residual dust and grease, let dry, then apply masking tape.
Sanding Tips
If you need to sand, keep in mind that sanding makes a mess, so first lay down some drop cloths under and around your work area. Sanding bottom paint also creates toxic dust, so use a dustless sander. And protect your exposed eyes, skin, and lungs with high-quality protective equipment before you begin sanding.
Masking Tips
For the cleanest line, try to position the masking tape as close to the boot stripe as you can, beginning at a natural start point in the line. Draw the tape out slowly, outlining every 1.5 to 2 feet. In addition, mask around underwater metals to protect them from contact with any copper-based antifouling paint.
Use 80-grit sandpaper to sand the entire bottom to smooth it out and remove any high or uneven spots. Sand lightly so you don’t sand through a protective barrier coat or damage gelcoat. After sanding, wipe down the surface using the solvent recommended by the bottom paint manufacturer.
Wiping
After masking, and before painting, wipe the surface with a clean, lint-free cloth to remove any residual dust or dirt.
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