How to paint your sailboat topsides with two-part polyurethane
why use two-part polyurethane?
If you decide to tackle painting your topsides, you’re starting a fairly big job no matter what the size of your boat.
However, you do have an alternative – you can pay a professional $200-$300 per foot ($825-$1000 per meter) to do the job for you.
If that number frightens you and you decide to paint the topsides yourself, you should know that you’ll spend 80% of your time preparing the hull for painting and 20% of your time actually painting.
So, having spent all that time on preparation, it seems reasonable that you should use the best possible finish you can.
If you’re looking for a finish that:
- lasts at least twice as long as the one part product
- has better abrasion resistance
- has better chemical resistance
- has better UV protection
- and looks at least twice as good as a one part product.
you should use a two-part polyurethane.
the new polyurethanes
Up until recently two-part polyurethane was the preserve of professional spray painters. But today many paint manufacturers including Epifanes, Pettit, Awlgrip, Fabula, Insignia, Blakes, Seajet, Sterling and International (Interlux) are producing two-part polyurethane’s that they say are suitable for application by the roller and brush method.
That is, suitable for painters like you and me.
International, or Interlux as it is known in the US, has a product called Perfection which has been produced specifically for non-professional painters using the roller and brush method of application. By all accounts painters like you and I can achieve excellent results with this product as long as we followed the directions for preparation and painting outlined in their bulletin available here
things you should know about Perfection
- You cannot paint over any one-part polyurethane or Alkyd marine paint. You must remove all the old paint before painting with Perfection. Old paint should be removed with a paint stripper. Do not sand the old paint off as you will contaminate the gelcoat with the old paint.
- You cannot paint timber hulls except diagonal plank or strip plank hulls covered with epoxy finish. Two-part polyurethane on clinker or lapstrake hulls will crack as it is not flexible enough to absorb the movement in these hulls.
- Perfection’s high-gloss finish will highlight, not hide, any underlying imperfections in the hull. So preparation is very important.
- It can be applied over gelcoat, epoxy finishes and other two-part polyurethanes.
- Perfection should be applied in dry, calm condition and out of direct sunlight. Temperature should be between 50 and 85°F (10 and 29°C) and humidity less than 65%.
Painting two-part polyurethane by roller and brush method is relatively simple. You’ll need good quality, high-density, closed cell, solvent resistant foam rollers and China bristle or Badger hair brushes for tipping off.
To apply the finish the paint is rolled on in thin coats and then tipped off with a brush to eliminate any air bubbles in the paint film. Tipping off is done vertically. It is best to work with a two-man team, one cutting-in and rolling and the other tipping off, always maintaining a wet edge. Clean and change the brush every 20 minutes and use a fine line masking tape such as 3M.
Practice makes perfect
You don’t want to go out and buy your paint, thinners, rollers and brushes and start painting your boat. You need to practice first. You need to get a feel of what you can do with this paint.
Two-part polyurethanes are sensitive to temperature and humidity and you need to understand how humidity and temperature affect the way the paint goes on.. You need to have an understanding of the amount of thinner you should be adding to the mixture for your conditions.
You could go out and practice on your dinghy or a surfboard, but by far the best idea comes from that guru of boat maintenance – Don Casey.
the glass method
Don recommends you practice on a sheet of window glass.
This will give you a very good idea of how the paint will flow on your hull, and you’ll be able to see the results of adding more or less thinners to your mix.
Don also recommends you cut a foam roller into three sections and buy a 3 inch roller frame. This way you get three small rollers and can do three test panels for the price one roller.
To do your tests on the glass, clean the glass thoroughly and stand it upright. Mix about 3 ounces (100 grams) of paint, that is 2 ounces (60 grams) of base coat plus 1 ounce (30 grams) of curing agent – and add about 1 teaspoon (5 grams) of thinners. Record the temperature and humidity. Using the small roller, apply the paint to the glass and immediately tip off with your brush.
If you can still see the brush strokes after three minutes, you need more thinner in the mix. Add a few drops of thinner and do another test with another roller section. If the paint sags or runs, you need less thinners. Mix another batch with less thinner and do another test.
Continued to test until and to get it just right.
You’ll be amazed at the results you can achieve.
check out the Perfection videos