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Leif Erickson

Leif Erickson

Blisters

Although fiberglass boats are mostly indestructible, one disease that can cause serious problems is osmotic blistering. In this conversation “All About Blisters” Leif Erickson discusses causes, cures, and prevention.

What Are Blisters?

Blisters are formed under the waterline when water moves from outside the boat into the fiberglass structure due to osmotic pressure. They show up as bubbles on the surface; if you pop them they smell like the styrene used in the boat’s manufacture. They are a real problem: difficult to deal with and expensive to repair. But they have to be removed because left unchecked they attack the integrity of the hull. Blisters can range from as small as the head of a pin to the size of a pancake. Your surveyor can tell you if there are any structural issues. The larger ones do more damage, breaking down the integrity of the fiberglass.

Blister Repair

If you just have a few small blisters, repair them individually when the boat is hauled out. But if you’ve got thousands of blisters, you have to peel the bottom. It can cost $500 per foot and up. First you have to remove all the coatings of bottom paint, then the gel coat, and finally a layer of fiberglass from 1/16 inch to 1/8 inch thick where the blisters are found. After that the hull has to sit and dry out. Once the moisture content is low enough, you can repair the hull by replacing the fiberglass you ground off with a couple layers of half-ounce matte and vinylester resin, then a barrier coat that is impervious to water, and finally replace the anti-fouling paint.

Drying Out

You have to let it air dry, once you’ve removed the saturated layer. Nothing else really works. We’ve tried heaters but it’s relatively ineffective and very expensive. The boat is going to be out of the water a minimum of two or three months, depending on the climate and how wet the hull is. It’s major surgery on your boat.

Worst Case

Worst case scenario is a cored boat that gets moisture into the core. That can be the end of the boat because repairing it might not be possible.

Avoiding Blisters

New boats have “better” fiberglass that is less prone to forming blisters. Manufacturers are adding barrier coats to new boats to keep the water from penetrating. Any boat without a barrier coat should have one added as soon as possible. Bear in mind, however, that it’s the amount of time the boat sits in the water that contributes to blister formation. In the mild Pacific Northwest, boats are normally left in the water all year (instead of hauling out for winter) and so boats might have more in-water time than say in New England. In an older boat, chances are you’ve got many layers of old bottom paint built up on the hull. Just removing those down to the gelcoat will make the boat more efficient, whether it’s power or sail. Once you’ve cleaned those off, it’s a great opportunity to add a barrier coat—it’s just like putting on a coat of bottom paint except it’s impervious to water. Then you can put on your bottom paint and get in step with current requirements for bottom paint requirements. It’s like killing two birds with one stone.

Bottom Paint

We’re seeing a phase-out of cuprous oxide around the world, just like we did with trybutyl tin. In Europe now, you can’t cruise with copper bottom paint. The good news is you don’t have to remove it, you can put a primer coat over it, and then use a compliant, non-copper bottom paint. You can do the same thing with tin. You’ll have the documentation from the yard so you can safely go to Europe without worry.