How to Paint Your Own Boat

Painting your own boat can be a daunting process for first timers, however I thought I would share my experiences from the several boats I have now painted.

JB Watercraft is all about DIY, and that goes for the prototype and promotional boats I build to my designs. That's why I decided to paint my own boat using the same type of paint system that my customers would likely use.

My Unicat has had a tough life with almost 10 years of use as a tender for a yacht and was looking very worse for wear. The paint was faded and worn thin, the keels forward of the rubbing strakes had been worn back to the plywood from being dragged up onto the dock after each outing, and the interior was dirty, with paint missing in many areas. The first job was to wash the boat and then strip off all the fittings so that I could paint underneath them. In my case I decided to leave the wheels on the transom as they make it much easier to move the boat around on my own.

Stripping fittings off the Unicat with help from our cat Sox.

With all of the fittings removed, and any remaining sealer or glue scraped away, its about time to begin something that anyone who takes on this job will become very familiar with; Sanding!

If the paint on the boat you are working on is still in fairly good condition with no scrapes, flaky spots or areas where it has been worn back to the substrate, you can simply give the boat a light sand with around 180-250 grit sandpaper to remove the gloss so the new paint will stick. This was not the case on my boat. I needed to repair the damaged keels, and the paint had been worn completely away in places so I sanded the worst areas right back to the fibreglass.

This stage in the process is also a good time to find out what sort of paint you have on the boat in order to make decisions about what sort of paint to buy and use. There are two main types: Single pot and Two Pot. Single pot is cheaper and is often easier to apply but is reasonably soft and less durable. Two pot paints are far more durable and can give a better finish. Two pot can be expensive but will normally last a lot longer. The important thing to remember is that single pot can be applied over the top of old two pot paint, but two pot paint cannot go over the top of single pot.

How do you know what sort of paint is on the boat? Fortunately there is a simple test you can perform. Take a clean, white rag and soak it in some paint thinner. Find an inconspicuous area in the boat and lay or tape the rag onto the paint surface and leave it for around 1 hour. Remove the rag and inspect the surface below. If the paint has bubbled, blistered or softened then you have single pot paint. If nothing has happened then you have two pot paint.

If your boat has single pot paint and you wish to paint it with two pot, you will need to remove all traces of the old paint first.

With all of the initial sanding work done, it's time for any filling and fairing work that may be required. In my case, with the repairs made to the keels, I had to re-fair much of the hull however it is unlikely you will need to do this if it is just a simple re-paint.

If you have dents or chips out of the surface, you should sand inside the damaged area with 100 grit sandpaper to give something for the filler to adhere to, then wipe clean with methylated spirits or isopropyl alcohol. Use an epoxy filler such as Epifill or mix your own using epoxy resin and fairing powder to the consistency of whipped cream.

When applying filler to a small area, use a soft putty knife or a bakers dough scraper. Leave the filler slightly higher than the surface so that it can be sanded back later, while trying to blend the edges into the surface.

Once the filler is dry, sand the filled area by hand using a hard sanding block, starting with 100 grit paper, and working up to around 200 grit as the filler flattens out. As you move to the finer grits, run your hands over the filled area. You should not feel any edge or lump in the area and it should blend smoothly into the surface. I don't recommend using soft sanding pads or power sanders for this job as the soft pads will not sand down the filler flush with the rest of the surface..

For my Unicat I went with the International Toplac system, partly because I already have a box full of the stuff in the shed, but also because I know it to be an easy to use system that gives great results. The Toplac paint system is designed to be rolled on and then tipped off lightly with the brush, a process well within the grasp of DIY'ers. As with almost all single pot marine paints, it is a 3 part system consisting of primer, undercoat and top coat.

As recommended I started with Yacht Primer, a high build single part primer which helps seal the surface and fills in minor imperfections. You can apply this using a roller and tip it off with a brush, however I usually skip the step of tipping off the primer as the roller creates a decent finish and it will get sanded back anyway. I always use Mohair rollers as they create a very smooth finish, and do not leave behind any debris unlike many foam rollers. They also have a longer lifespan than foam and can be washed out more easily.

The finished primer coats on the hull

Once the primer has dried overnight, sand it using 220 grit sandpaper on a hand sander with a foam pad. When sanding large areas such a as topsides or hull bottoms, always make 3 passes: Start with a 45 degree diagonal pass, starting at one end of the boat and working your way towards the other end. Follow this up with another 45 degree at right angles to the first. Finish with a longitudinal pass along the length of the hull. The purpose of this is to keep the surface fair and even, avoiding sanding hollows into the hull.

You can sand the primer using either wet or dry sanding. Wet sanding is excellent if you are working in a small space and want to avoid contaminating it with dust, however it can make it harder to tell when the surface is acceptably smooth. If wet sanding, lay old cardboard sheets on the ground to soak up the water and dust.

Repeat this process until the entire surface is smooth to the touch with no roller or brush marks.

Once you are happy with the finish wipe the surface down with a dry, lint free cloth to remove as much of the dust as possible. Follow this up by wiping the surface with a rag soaked in isopropyl alcohol (AKA Rubbing Alcohol), and then wiping off the alcohol with a dry rag. Always use new, white rags for painting, otherwise they can transfer their colour to the surface or leave behind contamination. Repeat this process until the rags come away from the surface with no visible dust on them. DO NOT use turpentine to wipe the dust off the surface, as it leaves behind an oily residue which the paint will not stick to.

You will more than likely need at least one more coat of primer, so apply this using the same method and then sand back with 320 grit and dust again. Be careful not to sand all the way through the primer as any bare spots will need to be re-coated. Once the second coat of primer has been sanded and dusted, it should feel very smooth to the tough and have a very slight sheen to it when viewed at certain angles.

You are now ready to apply the undercoat. This is like a fine primer with the ability to be sanded to en extremely smooth finish. It also helps the topcoat flow onto the surface more smoothly, providing a better finish as well as helping the topcoat to bind to the primer.

The undercoat I used is called Pre-Kote and is designed to work with the Toplac system.

The undercoat is best applied with a roller and then tipped off with a brush. Once again use a Mohair roller to apply the paint. Use light pressure on the roller, do not push hard as this results in a thinner coating of paint as well as potential runs as paint is squeezed from the ends of the roller.

Start at one end of the hull and work your way along to the other end. Roll the paint evenly over a small section of the hull, approximately 500mm long, and once you have covered this area begin tipping off with a good quality brush. Keep just enough paint on your brush to allow it to flow smoothly, the job of the brush is to smooth the paint out, not to apply any more paint.

Always start with brush strokes going length ways along the hull with one stroke for the whole length of the rolled area, then change to a vertical stroke, and go back over the same area. The vertical brush stroke is less visible to the eye when sighting down the hull, and for the undercoat it's also easier to sand. Use a very light pressure on the brush, just barely skimming the surface enough to knock off any roller marks, hence the name "tipping off".

Finished undercoat on the hull. I tinted the undercoat blue by mixing in a small amount of topcoat. This makes it less likely to show through the topcoat.

Once you have painted this small section with this method, switch back to the roller and start on the next 500mm section, overlapping the last section slightly. The reason for doing small sections at a time is that the paint sets quickly at first and if you roll a large area, you may find it too tacky to tip off properly. Work quickly and be sure to finish each section before the previous section has begun to become tacky. This is called keeping a "wet edge" and it allows each section to blend seamlessly into the next with no visible edge.

Work your way to the other end of the hull and then move on to the second side.

A second person is very helpful when painting as one person can roll and the other can tip off, however it's perfectly do-able with one person.

With the undercoat applied, let it dry overnight and then give it a light sand with around 300 grit sandpaper. Try to eliminate all brush and roller marks without sanding all the way through the undercoat. Use the 3 part sanding technique outlined before.

Once the undercoat has been sanded, you are now ready for the top coat. Once again, wipe the surface down thoroughly with Isopropyl Alcohol to remove all contamination. Ideally top coating should be done inside in a dust free environment, but if this is not possible, choose a day with little to no wind and a mild temperature. Painting below 5 degrees Celsius can affect the gloss of the paint and painting in high temperatures above 35 Degrees Celsius makes the paint cure so fast that it is difficult to apply. I also recommend not painting late in the afternoon or evening as the cooling temperatures and condensation overnight can cause a loss of gloss on the paint.

A small amount of thinner is normally required, especially on warmer days, but only use the correct thinner for the paint. Traditional products such as Turpentine and linseed oil should not be used to thin modern paint!

Apply the topcoat with the same roller and brush method as you used with the undercoat, keeping the paint coating thin and even and avoiding adding any extra paint with the brush. It is always better to do several thin coats than one thick one! Remember to paint small sections at a time to keep a wet edge and help it all blend nicely into one. Otherwise enlist a helper to roll the paint on while you tip it off. Once the paint has dried for at least 24 hours, the paint can either be sanded back lightly with 300-400 grit paper or lightly scoured with a Scotch Bright or similar abrasive pad. This provides a slightly textured surface for the second coat to stick to.

Any runs in the first coat can be sanded back carefully by hand using a hard sanding pad. At the topcoat stage, I highly recommend wet sanding as it helps keep the dust to a minimum.

Finished the first topcoat on the hull. Now needs to be sanded and re-coated

Once sanded, the second coat can be applied using the same method as the first. You will always need at least 2 coats of paint, possibly even 3 if you are using lighter colours.

I have worked at several marine chandlery stores over the years and customers asking for advise on paint often stated "I'm in a hurry and want a paint that only needs one coat!". My response was always that no such product exists. Any paint worthy of being called a marine paint will need more than one coat to achieve a good looking and long lasting finish.

Once your final coat has been applied and you are happy with the finish, you can remove the masking tape and call it job done. From here the only thing needed is a good wash and polish every 6 months or so to keep it looking good.

The finished paint job!