Monday, 8 July 2013

Preparing a GRP boat for Painting

See latest View from the Galley for delicious timely tips!

So, this week the weather has been more reasonable and I’ve been preparing the cockpit for painting. I
started sanding a while ago and I’m still on the job. It’s the worst part of the boat in terms of wear and tear and so I recon if I can get this bit right, then I should have no fears about the rest. In undertaking the job I’ve used two books as guides:-

The Fiberglass Boat Repair Manual (Alan H Vaitis, International Marine Ragged Mountain Press McGraw Hill, 1988, ISBN 0-07-156914-6)


Sailboat Refinishing (International Marine Sailboat Library) (Don Casey, International Marine
McGraw Hill, 1996, ISBN 978-0-07-148658-3)

Although at times they seem to contradict each other, both suggest that preparation of the surface is the key and that as an amateur I should devote 90% of my time and effort in this area. Initially, I was hoping to get by with cleaner, compound and polish, but having sanded away the old paint, its fairly obvious why some previous owner opted for a paint job.

Before that however, I had to deal with the problem of silicon – which may or may not be contaminating the gel coat. It seems old boats often have a coating of silicon due to previous owners polishing then with inappropriate products. An automotive polish for example will probably contain silicon and, whilst it is good for cars, it can be a problem for anyone wanting to paint over it. Strangely, I could obtain little information regarding the damage it can do. Suffice it to say, I was frightened enough by all the dire warnings to seek out advice on eradicating it from old GRP surfaces.

Some paint manufacturers tell you to use silicon removing products that they manufacture and market but I could obtain none of the recommended products in this corner of France. In desperation I spoke with a local chandler who told me that many marine paint manufactures try to increase their sales of products by insisting that only their products should be used. By way of example he explained that International Paints suggest that their paint customers should purchase their particular brand of thinner, International Thinners No 1 for cleaning brushes and diluting paint.  According to this particular chandler, International Thinners No 1 is actually nothing more than White Spirit which can be purchased at any home deco shop for a fraction of the International Paints recommended price.

Likewise, he suggested that any strong marine detergent / degreaser should be powerful enough to remove silicon traces (if there are any, and who can say?) but, my chandler also suggested that if I really want to be sure, I should wipe the gel coat with Acetone. Once again, it’s much cheaper from a supermarket than a chandlery. All this has to be done before sanding however. The published advice I have been relying on suggests that sanding a silicon contaminated hull will only drive the silicon deeper into the gel coat thus making removal so much harder.

Well I used an Eco Friendly French detergent / degreaser and followed up with an acetone wash before sanding commenced so time will tell if I got it right – or not.