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Time to end that blistering performanceBy Fred Barter |  | |
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Picture from International Paint's very helpful and comprehensive Gelshield application manual.
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Fabulous stuff fibreglass. It's hard-wearing, light-weight, easily formed into intricate shapes - no wonder it's become the first choice in boat-building. No maintenance too, so it seems on the surface. Until the blisters appear and you start worrying about costs. Will your boat lose value? Can you think of selling it like that? Worse still, will it hole through and you'll sink?
Well, blistering is not the end of the world. But now that winter's coming and you're likely to have the boat out of the water, you should certainly take the opportunity to do something about it. It's not a superficial problem either, so it won't go away just letting the hull dry out. Because though you might think those are just bubbles in the paint, they're not. They're actually in the outer layers of fibreglass. Which means like it or not, fixing it does take a bit of work.
Blisters start from voids or airspaces in the gelcoat and the fibreglass layers. The more obvious are about the size of a two-pence piece, with others like pin-pricks hardly visible to the eye. Nearly all fibreglass is affected, because of naturally-occurring voids in manufacture. Some lucky owners may never see anything. But just about every hull has the condition, even in fresh water.
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Strangely enough, blistering is part of fibreglass's success. All those millions of tiny strands of glass are bunched tightly together with air spaces between, then bonded by polyester resin forced through them. The air spaces make it tough and light, like a honeycomb, and the resin is incredibly strong. Even so, though it's coated with gel and a protective layer of paint, like wood or steel it's still susceptible to the effects of water. All the time you're sailing about, a chemical reaction is taking place below the waterline - sometimes slow, sometimes fast, depending on salinity, temperature and the million other variables that happen in living, moving, organic fresh or salt water.
Fortunately, the blistering effect is usually confined to the outer layer, either in or just under the gelcoat, so that a proper strip-down and new osmotic protection should keep you cruising happily for several more seasons. So get the boat out of the water and set to, taking off the paint and anti-fouling with a good paint remover, down to the existing gelcoat. If the problem is serious, you'll have to go further - perhaps with a gel planer, to get the fibreglass itself.
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To get the paint off, we decided to use this goo - International's Interstrip Paint Remover. Why? Because it doesn't make you pass out from fumes and you can whack it on in one thick, sludgy application and let it do its stuff. The trick is also to cover it with clingfilm to keep it moist, as it takes about 24 hours for the paint to soften from the primer. After that, it comes off pretty easily with a sharp scraper - just blunt the corners first so you don't make gouges in the fibreglass.
The messy bit is sanding the hull down, ready for the protective layer to go on. Don't forget, you're dealing with fibreglass, so wear all the protection you can get - goggles, face mask, gloves, long sleeves. You don't want microscopic bits of glass getting at you, if nothing else it itches like hell. Be careful with patches where you're down to bare laminate. You've got to fill those with watertight sealer - International's product is called Watertite - though if you're dealing with large areas, they recommend Gelshield Solventless Epoxy. Sand the whole lot thoroughly with 180 grade wet or dry paper before the next stage.
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Once the hull is thoroughly dry, the protection to go on is an epoxy coating that should be applied in several layers - at least six to be sure of keeping the water out. The name on the tin is "Gelshield 200" which comes in a two-pack, one grey, one green. That's because International suggest a dead sneaky way of making sure you cover all the bits of hull evenly - by alternating colours from layer to layer. A final coat of grey is probably the best, as a base for whichever antifouling you're going to apply afterwards.
Once you're back in the water, let's hope the only blistering you experience is the heat of next summer's sun as you sit back and break open the beers. Go on, you've earned them.
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