Monday, 12 August 2013

How to Paint a GRP Boat

Well this is my final report on painting the GRP cockpit of my ancient Westerly Nomad. 

The final report because I don’t want to think about this subject ever again and also because I did finally manage to get the job done – and I have to say, I am pleased with the result. So I've taken some time out to go fishing.

The whole process was dogged by unusual weather in the form of heat wave temperatures, strong winds or threats of rain but I finally achieved two coats of Pre-Kote and two top coats of TopLac – a one pot emulsion produced by International Paints.

Now I don’t believe that having managed to paint the cockpit makes me any kind of expert but for the sake of anyone else considering embarking on this task, here is a brief summary of what I learned (mainly through the mistakes I made).

A professional will spend 80% of his effort on preparation of the GRP surface. As an amateur you should devote 90% on this task and that will probably take you 95% of the time. No amount of paint will cover or hide sloppy preparation. Preparation includes:

cleaning the surface to be painted;

washing with a degreaser and/or acetone to remove any possible traces of silicone;

removing as many fittings as you can so that you can paint underneath to avoid having too many ‘edges’;

filling holes, dings, cracks;

sanding, to smooth filling and other imperfections, to remove stains and to provide a key for the paint; (Start with 80 grade sandpaper and finish with 120 grade or even finer) *NOTE the lower the number the courser the paper

removing all traces of sanding dust and moisture;

masking off the edges.

Then, and only then, can you consider getting some paint on. There are numerous products available and without a doubt some of the best rely on two pot paint and hardener systems. They’re fine if you are confident with a paint sprayer and your boat is in a shed where you can control temperature and humidity. For the rest of us however, a more traditional one pot paint is more forgiving and it will give a better finish than a poorly applied two pot system.

Paint should be applied in thin coats. Some people prefer a brush, others like rollers. I tried both and finally settled on a cheap foam pad. Cheap disposable brushes are fine so long as they don’t shed hairs. Some people comb their brushes with a hair-comb and they swear it is a very effective method for dislodging loose hairs which might stick to the paintwork. Roller users should use small foam or very short haired rollers to avoid ‘orange peel effects’. A dry brush in you other had can be very effective in removing drips, runs, brush or roller marks before the paint sets. Paint should be applied in a union flag manner to help avoid obvious unidirectional brush marks on the finished job.

Do not underestimate weather effects. If the weather is too hot, the paint will dry as you paint and the effects will be awful, too windy and you get dust and if there is a hint of rain – do something else. Even on a perfect day, you will find that the paint behaves differently on different parts of the boat. So in areas where the GRP is in direct sunlight the paint will be quicker to set and less forgiving than in cooler shadier areas. Take a garden watering can with you and damp down the area around the boat to minimise dust.

I actually made a poorer job in areas where I was too careful, applying paint in minute quantities and brushing out too often for too long. As it sets it can drag and when this starts to happen it is best left alone. The areas where I was more confident were done much quicker and they produced the best effect. Keep checking back, especially corners and hard edges drips can be brushed out if you spot them soon enough. Apply the paint thinly, several carefully applied thin coats are better than one coat applied too thickly.

The good news is that if a coat goes wrong, you can always sand back to a smooth surface and apply a new coat – providing of course that you remove the dust after sanding. I had to do this with my second undercoat using 240 grade sandpaper – no harm was done.

I now have a problem however, - Finding the ideal weather conditions to get the four coats on took as many weeks and the masking tape is now probably welded to the gel coat. Ah well, that’s a problem for next week. Onwards and upwards!