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Old 05-07-2006, 04:17   #1
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Barrier paint

I recently posted a question about my wooden rudder and whether I should coat with epoxy prior to painting, I received tons of information. And I have decided to prepare the rudder well and just paint. My questions now is about the bottom. The boat was built in 1972, it appears that it has never had any issues with blisters, it is obviously fiberglass. I am being told by the guys in the yard I need to put 4-5 coats of Interlux2000e as a barrier coat before putting on the bottom paint. I have read some information that indicates this may also not be necessary, and in fact may not be a good thing. I really value the information I receive here and look forward to your opinions.


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Old 05-07-2006, 04:53   #2
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Mike and Paula,

The best paper I've seen on this subject is here:
Zahniser's Yachting Center: Chesapeake Bay Marina; Solomons
Go to "repair yard" then to "blister repair" then to "blister and laminate hydrolysis". No direct link to the paper.
Zahnisers is one of the best yards in the Chesapeake. You will get a lot of stories on "osmosis", but Zahnisers paper will give you the facts.

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Old 05-07-2006, 06:13   #3
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Excerpted from the excellent paper, as referenced by Rick I, at


<quote ~ in part>

“... We are occasionally asked about preventative use of barrier coats over an existing, unblistered gelcoat. Unless the boat has only been in the water for a few years, getting the bottom sufficiently dry without removing the gelkote is a very slow process, often 12 to 18 months. The gelkote, while not sufficiently waterproof to prevent blistering, is still dense enough to slow drying down to a snail's pace. Most boat owners are not willing to give up their boat for a year for a preventative measure. Considering the work will cost half of a blister repair, most owners opt to wait until the bottom blisters. Never the less, a properly applied barrier coat will greatly reduce hydrolyzation over the years. The cost of maintenance of this barrier coat will, however, be rather high.

In the case of a new boat, however, if the manufacturer has not applied a barrier or built the boat out of a non-blistering material such as vinylester resin, a barrier coat is highly recommended before the first immersion. It won't last forever, but it will forestall hydrolysis and blister formation. This is especially important if the boat builder does not have a definite, long term, written policy on blister repair warranty ...”
<end quote>
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Old 05-07-2006, 21:14   #4

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Mike, if you clean down to the bare bottom and find you don't have a blister problem...then barrier coating is a damned expensive way to protect yourself from a problem that probably will never affect you. It can't HURT...but blistering is very much related to the particular fibgerglass materials and practices, and if your hull hasn't had a problem yet, I doubt it will, unless something gets very different. (i.e. if it was kept hauled 9 months every year and sailed in cold water, and you're planning to keep in in warm water 24x7 for the next five years.)
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Old 05-07-2006, 21:31   #5
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Yep the above replies have all touched on a very important question to find the answer to first. What was the resin used. If it is vinylester, you don't need to worry about pox.
There is one big problem with applying barrier coats to hulls that have been emersed for awhile. If the hull has drawn in water, the barrier coat effectively captivates it and this can also cause blisters. It is actually why barrier coating got a bad rap at one stage. Barriers were applied and blisters appeared and so the blame was put on the barrier, when in fact, it was the hull not being fully dried out before the barrier is applied. Which brings me to the finish with, if a barrier is being applied to stop moisture being drawn in to the hull, then the hull must be totaly and compleatly dry first.

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Old 05-07-2006, 21:35   #6
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Barrier coating is not expensive, compared to the alternative.

The alternative being blisters and a wet bottom. Which will require, at a minimum, peeling the bottom of gelcoat and nonstructural fiberglass, followed by drying of the hull until it reaches the acceptable level of 10-15% wetness.

Then you fair the bottom and apply barrier coat and hopefully your bottom is fixed for good if it is properly cared for.

Barrier coating a dry hull as a preventive measure is very INEXPENSIVE, IMO, assuming it protects your boat succesfully.

I have been through all this and I know how expensive the entire process can be. I barrier coated with a relatively new product from Seahawk. I don't know uet if it worked, boat's only been back in the water for about 4 months.

on edit: One cannot assume that an older boat that does not have blisters will not eventually be so afflicted. If the boat has been in relatively cold water all its life and is regularly hauled to allow the hull to dry out, that will almost always prevent blisters. If that same boat goes to Florida or the tropics and stays in the water year round, I can safely predict it will blister. This does not take into account what kind of resin was used. I am not sold on vinylester, but I'm willing to give its proponents the benefit of the doubt until, and if, they are proven wrong.

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