There is literally an A-to-Z (algae-to-zebra mussels) assortment of marine life waiting to make the bottom of your boat its home, which is why antifouling or bottom paint is so important to protect your boat against marine growth. A clean hull ensures that your boat performs at its best speed, maneuverability and fuel economy.
When the paint needs to be refreshed, owners usually paint over previous coats, and while this is acceptable for a few seasons, you eventually need to strip all the layers and start with a new coat of paint.
The most common ways to remove bottom paint are sanding, sand blasting and soda blasting, but there is another method: applying a removal chemical and then scraping the bottom paint away. That’s what I did recently on my boat before applying new bottom paint. Here’s how.
The easiest way to remove and apply bottom paint is to have unobstructed access to the hull, and therein lies the potential rub. The biggest obstacle for a DIY bottom-painting project is safely removing the boat from its trailer, which I covered last month in Boating World (DIY, “Separation Anxiety,” p. 26). Whether you use my method or one of the many ideas you can find online, remember this: Boats are heavy! Be sure you safely secure the boat to the support system.
You must thoroughly wash the hull before applying bottom-paint remover. I used a bucket of soapy water, since my boat is in my garage. If you are working outside, you could use a water hose or a pressure washer. Once the hull is completely dry, use painter’s tape to protect any areas you don’t intend to paint.
I decided to use Marine Paint Remover from West Marine ($59.99/gallon). In addition to being environmentally friendly, it is described as being able to remove five layers of paint with a single application. One important note: The container states in bold letters, “Stir only. Do not shake.” James Bond would be disappointed.
At a hardware store, I found a $10 painter’s kit with everything I needed to apply both the remover and the paint: one brush, three roller brushes, a paint tray and a can opener (picture 1). I also bought two paint-tray liners, a metal paint scraper and a plastic drop cloth.
I covered the area under the boat with the drop cloth, placed a liner in the tray, stirred the remover — a fluorescent light-green color — and then poured it (picture 2). I used a roller brush to apply it (picture 3), but you can use a regular brush or a putty knife. The remover needs to be applied thick; it should have texture to it. I used one gallon to cover the bottom of my 16-foot boat.
When the paint-stripping action is complete, the remover turns off-white or light blue. The color change may take anywhere from four to 24 hours, but you can actually start removing it before the color change.
Scraping the Bottom
After about six hours, the remover changed color and appeared dry and flaky. I used a metal paint scraper to test scrape a few areas of the hull (picture 4), used a paint brush to apply more remover to areas where the paint was harder to strip (picture 5) and waited about an hour to rescrape those areas. Some of the paint wouldn’t come off with the scraper, so I used a wire brush and a metal putty knife to remove it. Once the paint was scraped off the bottom, I lightly hand-sanded it — first with 150-grit, then 220-grit sandpaper — to smooth out the bottom’s surface before washing the hull and allowing it to dry.
Paint the Town
For my new bottom paint, I selected West Marine’s BottomShield black ($129.99/gallon), which requires vigorous shaking before it is applied. You’d be smart to use a mechanical paint shaker at a hardware store.
Using the second tray liner and a fresh roller brush, I began to apply the paint, starting at the bow and working my way aft with long, slightly overlapping brush strokes. West Marine’s paint covers approximately 400 square feet per gallon, and if you are applying several coats, allow each coat to dry before applying a new one.
Don’t forget to paint the areas that are covered by the structures supporting your boat. You will need to reposition your supports, and be careful when doing so. Make sure the boat is secure and stable. Once it is, follow the same process to remove the old paint and apply new paint to the areas. When you are completely done applying new bottom paint, wait another 24 hours before reuniting your boat with its trailer.
The better job you do removing old bottom paint and applying new paint, the better job it will do protecting your boat. If you don’t properly CYA (cover your asset), marine life certainly will.
Note: Any unwanted paint, remover, or paint-covered items should be disposed of at a Hazardous Household Waste collection facility.