August 8, 2013

Beware of barrier coats

IS A BARRIER COAT a good idea to keep your boat’s hull free of blisters? The advertisements say it is . . . but beware. It may be a complete waste of time and money. It may even make things worse.

A few years back I decided to take all the old bottom paint off my 1983 Cape Dory 27.  It consisted of numerous layers of hard epoxy anti-fouling and I had the impression that this job had never been tackled before.

I had a shoulder injury at the time, but I hauled her out and started removing the old paint in small sections, about 5 feet by 2 feet every day.  I used a chemical stripper and a hand scraper. It took me several weeks of hard labor to get down to the gel coat all over.

Then I washed the whole hull down carefully and applied Interlux’s Interprotect barrier coat system, following the instructions to the letter.  I did alternate coats of white and grey epoxy and then I painted the bottom with two coats of Interlux Ultra antifouling.

It all looked very splendid and I was pleased that I had taken the extra trouble to put on a barrier coat, having taken all the old paint off anyway.

But two years later, when I had the boat hauled out for repainting, the bottom was covered with hundreds of small blisters under the barrier coat.  I could have cried. A marine surveyor who looked at it for me just laughed.  It wasn’t a structural problem, he said, just cosmetic.  He advised me to sand right down to gel coat again.

“What made you apply a barrier coat?” he asked.

“I just thought it was a good idea.  Having done all the hard work to get the old paint off, it seemed like an ideal opportunity to protect against blisters.”

“Did you have any blisters before?” he asked.

“No,” I said.

“So she has spent more than 20 years in the water without forming any blisters,” he pointed out.  “What made you think she would suddenly get blisters now?”

“Advertising,” I said.  “The adverts say it’s a good idea.”

After a while, we both had a little chuckle at that.

The lesson I learned is that the fiberglass hull must be absolutely dust-dry before you can apply a barrier coat.  I don’t mean just surface dry.  It has to dry out for months.  If there’s the slightest suspicion of any moisture trapped in the fiberglass it will simply form blisters beneath the barrier coat.

Since then, I have read about many others experiencing the same problem.  “It seems the marine industry is always trying to sell us something,” said one boat owner.  “For some boats, a properly applied barrier coat might be beneficial.  As for the vast majority of boats, I would say if it ain’t broke, don’t fix it.  I never imagined the prevention I thought I was providing would become the problem.”

I regret to say I know exactly how he feels.

Today’s Thought
Any man may make a mistake; none but a fool will persist in it.
— Cicero, Philippicae

“Did you buy that new book on schizophrenia?”
“Not yet. I’m in two minds about it.”

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)

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