The way to get the best end result before applying primer to your boat is to do a lot of preparation. Boats made out of different materials must be prepared differently. This includes the way they are sanded, washed, and painted. When applying your primer, don't stress too much about the finish, as it gets covered by the anti-foul or topcoat of paint.
Firstly, you must wash down your boat. You need to get everything off your boat whether it be dirt, sand, marine life, or seaweed. You can use a high pressure hose, a scraper, or rags. There are some products on the market that can help with this process and help with the removal of wax. However, do not use acetone as it flashes too quickly and does not remove all the surface contaminants. If using one of these products, either follow the instructions on the product, or if no instructions have been provided, then use the following:
- Use the wax remover generously so that you wipe off the residue; do not just spread and smear it around. Apply the dewaxer using the two rag method: one rag to apply and one rag to remove. As you will be needing to change rags often, make sure you have plenty of clean rags handy.
- Applying over a 2' x 2' section at a time to ensure that every bit of the boat has been covered. Continue doing this until the entire boat has been done.
- Lastly, wash the boat with a strong detergent that includes TSP (Tri-sodium-phosphate). This further helps degrease the surface.
Next, fill any dents or gouges. You can fill any gouges with an epoxy fairing compound. When applying the putty, let it stand 'proud' above the surrounding surface so that it can be faired and smoothed when you start sanding to get an even finish. Rough sand the patch with 60 grit before switching to 120 grit to get the final contour.
When sanding your boat, there are a few things to take into consideration:
- If the coat of paint you have on your boat is flaky or damaged, you will need to strip it and sand it away completely.
- If the old paint is a different type to the one you plan to apply, then remove it completely.
- NEVER use a belt sander on your boat.
It goes without saying, make sure you are wearing all the appropriate PPE (personal Protection Equipment), but take particular care to ensure you are wearing eye protection as paint chips are toxic.
Now that you are up to sanding and applying the primer to your boat, it depends what material your boat is made out of. Depending on whether it's made of wood or fibreglass, there are different processes that must be done to get the best possible finish.
If you are preparing and painting a wooden boat, there is a different process for both previously painted boats and unpainted boats. If the boat has been painted previously, and the paint has been looked after, you can sand the boat with 220-grit paper to knock off the gloss. This will help expose some paint that is blistered or flaking, which will need to be scraped off. If you have these spots, they will need to be sanded down to bare wood. Such areas should have a coat of filler type primer applied and be hand sanded to 'feather' them into the rest of the existing paint. If the boats' paint has been neglected, it must be removed entirely. Once the old paint is gone, prepare the hull as if it were new bare wood that hasn't been painted before. Bare wood that hasn't been painted before should be sanded with 80-grit paper before application of a filler type primer. The main purpose of this primer is to fill in the grain of the wood. Allow the first coat of primer applied to dry for 24 hours before sanding with 220-grit sandpaper. You will want to sand it down to the thinnest possible paint film without sanding down to bare wood. Some bare wood will inevitably show and require a second or third coat and sanding. Primer coats and sanding should be continued until the grain of the wood is completely filled and the surface is smooth.
When painting a boat made out of fibreglass, you need to sand the gel coat with 80-grit sandpaper, as the gel coat is so slick and has such low porosity that paint has a hard time adhering to it. There are primers available that chemically soften the gel coat and bond to it prior to applying the first finish coat of paint. Always choose a primer that is compatible with the finish coat of paint. Apply two coats of primer, sanding in between the coats, and then sand the entire surface with 220-grit sandpaper. When sanding, always use a sanding block, whether it be rigid or foam, to ensure that you do not add any dips in the surface that may appear in the finished surface. The following day, wet sand the entire area with 220-grit sandpaper and lots of water. Also do a thorough water wash and a full wipe down with thinner, rotating and throwing out the rags every couple of feet, then paint it again.
When applying primer or paint to a boat, a recommended approach is the 'roll and tip' method. This is when one person rolls a thin coat of paint and the second person follows the roller with a brush tipping out the edges left by the roller. The brush removes the 'stipple' created by the roller and produces the smooth finish. When painting, roll the paint on in about a 2' x 2' square area. Roll out the paint in a big W and then re-roll the dedicated area to distribute all the paint evenly in the 2 foot square area. First roll horizontally, then tip vertically with a good unloaded 3" bristle brush. Each time the tipping brush is used, clean it with solvent. This keeps the brush from loading up and brush strokes in the paint fine. You will need to work and move quickly and efficiently because if you move too slow, the paint will already be setting and the brush strokes will not level out.