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Old 03-27-2000
Don Casey Don Casey is offline
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Barrier Coats for Blisters

I've got a blister problem, and I read in This Old Boat that painting the bottom with a silicone-based enamel with long Alkyds would be better than with epoxy since it wouldn't have as adverse a reaction as epoxy if water were to permeate it. Does this still hold true?

Michael Borga

Don Casey responds:

Michael,

At the time I recommended the blister treatment you cite, a typical epoxy barrier was one to three coats. Alkyd enamel was just as effective, without making matters worse. Since then, the prescribed application has evolved to at least 20 mils of epoxy—at least six coats; usually seven or eight. At this thickness, epoxy does a reasonably good job of resisting permeation—much better than paint.

Unfortunately, dealing with blisters can be far more complicated than just slapping on a barrier coat, depending on the reason for the blisters. A lot has been written about blisters in the last 10 years. I urge you to do a little research before you attempt repairs.

Don