MIX AND MATCH
Unfortunately, now comes the hard part, and everyone has the same benign-sounding opinion about mixing pigments into the gelcoat to match the existing colour of the hull. “It’s a bit of an art,” explains Groen. (“It’s an art,” echoes Jamie Hewitt. “It’s a little bit of an art,” adds Little.) And by this, of course, what they really mean is that it’s not a science; careful measuring alone guarantees nothing when you’re mixing colour; there is just trial and error, frustration, and a couple of warnings.

Gelcoat is a two-part system made up of a particularly dense form of polyester resin and a hardener (methyl ethyl ketone peroxide or MEK). On a warm day, once they’re stirred together, you have about 20 minutes of working time – depending on the amount you’re mixing. So the first warning is that you should add pigment to the resin and finalize the colour you need before you add any catalyst. That’s obvious, right? And so is this once Hewitt points it out: “Mix all your colour at once, then add hardener to the small amounts you need as you go.” That way, each layer you apply will be the same colour as the last one, and if you repair more than one spot, they will all at least match each other. Finally, be scientifically precise with the catalyst. Read the instructions. Too much hardener will change the final hue.

Once you have the colour more or less right, you can apply the gelcoat to the prepared area. Use a Popsicle stick or a plastic scraper or even a plasticized playing card to lay on as smooth a layer of the gel as possible. Keep in mind, of course, that “smooth” is an illusory ideal. Also keep in mind that you’re going to be sanding this whole area again after it sets anyway. Slightly overfill the hole to allow for shrinkage, and in cases where you need to fill a deeper depression, plan to build it up with two thinner coats, with a light sanding between. Now go away until tomorrow.

PUTTING ON THE POLISH
It bears noting that at this point the real job is complete. Gelcoat repairs are necessary in order to protect the fibreglass, and once you’ve done the prep and laid on the gelcoat, that end is achieved. From here on in, it’s all about aesthetics.

Carefully sand the area again using 120-, then 150-grit on a hardwood block to smooth out irregularities. Once you’re satisfied, Groen suggests you widen your work area slightly by moving the masking tape back a bit so that you see shine all around the patch area. You want the final coat to feather out onto the previously untouched surface, so use the 150-grit to rough up a narrow perimeter.

Apply a final layer – it shouldn’t reach all the way to your masking tape – and then, well, leave it overnight again. Next morning, you can begin sanding with 400-grit wet-dry sandpaper and progress to at least 600-grit or even 1,000-grit for highly visible spots. At that point, you can remove the masking tape and switch to rubbing compound buffed either manually or with an electric polisher. Note that, like sandpaper, rubbing compounds come in varying degrees of coarseness; for general duties like this, regular-grade should do the trick.

Finally, if you want to get really obsessive, apply a coating of wax. This is something that you might consider anyway since, on a newer hull, a good UV-blocking wax will preserve that deep gelcoat colour for a few years longer before it starts to oxidize and become chalky.

With luck, the finished patch will, more or less, match the hull. As Hewitt says, “I figure that anything you can’t see from three feet away is a success.”

Honey Harbour cottager Tom Carpenter owns a welded aluminum boat.

Adapted from "Scratching the Surface," published in the July August 2004 issue of Cottage Life.

Copyright © 2004 by Cottage Life. All rights reserved. Reproduction of any article, photograph, or artwork, for other than personal use, in whole or in part, without the written permission of the publisher is strictly forbidden.