Maintaining your boat’s painted surfaces and periodically repainting the boat is important for more than just your boat’s appearance. Marine paints and finishes help protect your boat’s hull, deck, and other surfaces from the harsh effects of the sun, the corrosive effects of salt water, and algae and barnacle growth. Here are some step by step instructions to help you get the best results when painting the bottom of your boat.
Preparing your boat for a bottom paint job doesn’t have to be difficult — but knowing what to do, and in what order, is essential.
The best time to clean and prepare the bottom of your boat is when you haul it out at the end of the season. Once you let the slime and growth dry and harden it is much more difficult to remove. The easiest method is to have your boat yard pressure wash the bottom as soon as they haul the boat. If your old bottom paint starts flaking off, you should get a scraper and remove all loose flakes. You might want to consider using a paint stripper and removing the old layer completely if the paint is in poor condition.
When to Strip Old Paint:
Remember that the adhesion of the new paint is only as good as paint that it is being applied over. So watch for signs of adhesion failure. Anywhere the old paint is flaking or lifting, the bottom needs to be stripped. You may also have to strip the bottom if you are changing the type of paint. For example, the aggressive solvents in vinyl paints lift other types of bottom paints, so if you are applying vinyl, any non-vinyl paint has to come off. And soft, sloughing paints are a poor undercoat for anything other than a fresh coat of the same.
If your bottom paint is in good condition you really only need to sand it a little with 80-grit sandpaper (you can use a finish sander or a random orbital sander), clean it up, tape it off and roll on another coat.
Antifouling dust can be a major health hazard and you really should be wearing a respirator and particulate filter as well as eye and ear protection for your own safety.
A hull that has not been previously painted has mold release wax on the fiberglass. That will interfere with paint adhesion unless you remove it. Clean the hull surface thoroughly with dewaxing solvent and plenty of clean rags. Sand the de-waxed hull lightly with 80-grit paper. Wipe down the area again to remove all sanding residue. Now apply a primer. Follow the manufactures recommendations for primer application.
You are now ready to apply bottom paint.
The antifouling in bottom paint is often heavy and will settle to the bottom of your can. Make sure you take the time and effort to mix your paint properly. If the copper isn’t evenly distributed, some areas of your hull will not be protected.
If you have a paint shaker, run it for at least 5 minutes to get the copper and the pigment evenly distributed throughout the paint. If you are doing it by hand keep dredging up the copper off the bottom of the can. Each time you add to your roller tray you will want to stir again to ensure consistency.
Roll the paint onto the hull using a short-nap roller cover (usually 3/8 nap). Wear sleeves and gloves to keep the paint off your skin.
Don’t add any thinner to bottom paint unless the manufacturer specifies otherwise. Fill your paint tray with paint. Dip your roller and roll it up and down on the hull. Each time you refill the paint tray, first stir the paint in the can to keep the copper in suspension.
By the time you work all the way around the hull, many bottom paints will be dry enough to overcoat. Check the specifications on the paint you are using. A second coat is usually recommended and will increase the life of almost any bottom paint; copolymers benefit from 3 or 4 coats. No sanding or other prep is needed between coats. Once the paint dries to the manufactures specifications, you are ready to launch.
Be sure you leave all zinc anodes unpainted. If you are installing new zincs make sure you do not paint over their mounting locations. Good electrical contact is essential for zincs to do their job.