EVERY TIME I SEE an advertisement for an epoxy barrier coat, I flinch. I am reminded of a terrible mistake I made while trying to waterproof the bottom of my boat. It was an attempt to make sure that my 26-year-old Cape Dory would never fall victim to the dreaded boat box, the blisters that knowledgeable people call osmosis. But it turned out to be a big waste of time, labor, and money.
It occurred to me one day that I should remove the great wodge of bottom paint that had built up over 26 years. None of my boat’s previous owners had bothered to scrape the bottom down to bare fiberglass. So, at the next haul-out, I set to. It took me weeks, working on my own, to remove all the old modified epoxy antifouling paint, and when it was all done I was very glad to see that underneath it all the gel coat was as good as new.
But I couldn’t leave well enough alone. The devil came to me during the night and whispered: “Now that you’ve got all the paint off, why don’t you apply a good barrier coat to prevent osmosis?”
“But she hasn’t got osmosis,” I pointed out. “Her bottom is perfect.”
“Ah, but she could get it at any time — especially now that you’ve removed those thick layers of paint. And besides, when would there be a better opportunity to barrier-coat the bottom? Everybody’s doing it, you know. You’ve seen the advertisements, haven’t you? Osmosis is a dreadful thing. You don’t want osmosis,”
Yes, I had seen the advertisements. And yes, the devil had his wicked way with me. I applied two coats of epoxy barrier coat, following the instructions meticulously. On top of that I applied two coats of modified epoxy antifouling paint. And so I went about my daily tasks smiling and whistling happily and thinking to myself that however my good old Cape Dory might deteriorate in the coming years, she would at least never catch the boat pox. Yeah, right.
Two years later, when she was hauled out for new antifouling paint, her bottom was covered in tiny blisters. I couldn’t believe my eyes. I called in a surveyor. He laughed. “Why did you put on a barrier coat if there wasn’t any osmosis?” he asked. “If a boat has been in the water for 26 years without blistering, there’s not much chance she’s going to get blisters now. What made you do it?”
“The devil made me do it,” I said.
“Well, you’d better send the bill to the devil because you’re going to have to remove the barrier coat,” he said. “It’s not a big problem — the blistering is between the gel coat and the barrier coat; it’s just cosmetic, not a structural problem — but all those pimples will slow you down terribly in light weather. Take her down to bare gel coat again, and just apply straight antifouling.”
Thus, I learned the hard way that you must never give a fiberglass hull a barrier coat unless the hull is absolutely dry. And I don’t mean surface dry, but dry right through. It can take many months for a hull to dry out, even if you use hot air to help it along. And you’ll need a moisture meter to find out if there’s still any water present in the layup. If there is, your barrier coat will simply seal it in.
The other thing I learned is that you shouldn’t barrier coat a hull that’s spend 10 years or more in the water without developing blisters. I would have saved myself a whole lot of time, labor and money if only I had remembered the wise old saying: If it’s not broke, don’t fix it.
What cannot be cured must be endured.
— Rabelais, Works
“Darling, will you still love me after we’re married?”
“Sure, why not? I’ve always been partial to married women.”
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