Cleaning and painting your boat’s bottom

Published 7:05 pm Monday, July 8, 2019

If your boat is out of the water is its bottom clean? Does it need bottom paint refreshed? A clean bottom improves running, handling and efficiency plus a painted bottom contributes to a clean bottom.

If boating in the Pamlico or Neuse Rivers plus Pamlico and Albemarle Sounds should you use fresh water paint or paint for salt water? The consensus is fresh water paint, even if you occasionally venture into the ocean.

Which paint? The brand is not important, though it should be consistent with the current paint, unless the old paint is removed completely for a new coat.

When a boat stays in water year round it should include a barrier coat between the fiberglass hull and bottom paint. A barrier coat protects from moisture intrusion causing blisters and is worth every penny invested.

Whatever you are painting, home or boat, the key to good, long-lasting results is preparation. Invest twice as much time in preparation as the actual painting. Step one in prep is washing or scrubbing the bottom to remove crud, barnacles, muscles and vegetative carpet. Use a power washer to remove surface dirt then employ a medium grade scrub brush to remove stubborn dirt. The bottom must be clean.

You can now assess the condition of the current paint. Does the boat’s bottom paint need to be replaced or simply need a touch up coat or spotting? In all instances, the bottom must be clean for any new bottom paint to adhere.

For a surface coat or spotting, once the bottom is clean, employ a sanding block to lightly rough the paint’s surface to improve adherence. When spotting where the gelcoat is exposed, feather the edges for a smooth surface. Inspect for and repair any blisters per manufacturer’s directions.

When total replacement is required, employ an 80-grit sandpaper to remove all old paint down to the gelcoat. Next use a higher grit sandpaper to smooth the gelcoat surface. A critical step to a smooth surface with maximum adherence is employing a tack cloth (multiple tack cloths) to eliminate all dust particles. First wash and dry the boat’s bottom. Then, when dry, employ the tack cloths, removing any residual dust. Finally, use a cleaning solvent to remove residue left by the tack cloth. A super clean bottom surface is necessary to achieve multi-year (3-5 year) protection.

Now the boat’s bottom is ready for paint. If a surface coat or spotting, select the same brand and paint type presently on the boat. Applying a different brand along with different type over an existing paint will degrade performance of the new paint surface. Remember, an epoxy barrier coat is strongly recommended for unpainted gelcoat to prevent water intrusion and blisters.

Select a bottom paint specific to your boating locale as well as use. Racing sailboats require a hard, extremely smooth surface for speed while a metal fishing boat needs a paint that keeps the bottom clean. Certain paints are specific to fresh water and others specific to salt water, while a few work well in brackish water like our rivers and sounds. Consult locally for the correct paint for your boating area.

You may roll or brush on bottom paint, depending on the desired finish. Rolling is OK for most applications. For a surface coat or spotting, a single application usually suffices. Employ a 5/16” to 3/8” nap roller for a seven millimeter wet thickness.

Apply two coats to unpainted gelcoat. Remember that bottom paint adds weight to a boat, reducing the vessel’s performance and economy, so a third coat really adds nothing to paint performance. Some boaters employ a different color paint when surface coating to visually see when a new surface coat or replacement is needed. Work from the keel to the water line. Allow adequate drying time between coats according to the manufacturer’s specifications and current weather conditions.

Consult the primary manufacturer of boat paint for exceptional print and online information about top and bottom paint, surface prep along with painting techniques. Local marinas and chandleries are excellent sources of local paint knowledge.

My thanks to Jessica Martin of McCotter’s Marina for her help in researching this article. This article is given courtesy of the Pamlico Sail & Power Squadron, America’s Boating Club. To learn more about our upcoming boating courses, email Linda, our Education Officer at or contact her at 252-964-3009 for upcoming public seminars and courses.

Biff Matthews is a member of Pamlico Sail & Power Squadron.