Marine plywood is a higher grade of plywood than that used around the home. It needs special care and attention when painting because of its immersion in water due to the effects of water erosion. Knowing how to paint marine plywood makes the difference between preparing a boat that will last years and painting one that will last only months.
Clean the boat thoroughly using a sponge and a bucket of warm water. It is essential when starting that the boat be free of dirt and other surface impurities that might otherwise be worked into the wood, as these can ruin your finish. Once the boat is clean, allow it to dry, then sand down the surface to remove any existing paint or paint fragments.
Paint the wood with a coat of epoxy resin. This will dry quickly in warm weather, so it is best to do this fairly quickly in order to ensure a reasonably even coat. Allow the resin to dry and soak into the marine plywood, forming a protective barrier. Sand down the surface to remove any “fuzzing” caused by the epoxy and apply a base coat of latex primer. Leave the primer to dry.
Check the plywood for holes, gouges and other surface imperfections. Fill these with the surfacing putty filler and allow it to set. Sand the filler so it is smooth with the rest of the marine plywood surface. Apply another coat of latex primer and allow it to dry. Finish off by painting at least two coats of part urethane paint.
Choose a colour of primer that will enhance the finish of your boat. Although with modern paints, it is difficult to see the primer underneath, a light-coloured primer will still “lift” or brighten the colour of your part urethane paint finish. Similarly, a darker primer will deepen the paint. Choose the colour of primer that will give your top coat the finish you are looking for.
Filler sets harder than primer, so it needs a little more effort to sand down. However, it can be easy to forget this when sanding, causing you to sand away the primer surrounding your filler. If this happens, you will need to touch up missing primer before continuing. When applying resin with a paintbrush, the resin will set solid and solvents to remove it will eat through bristles. Be prepared to throw the brush away.