Bottom paint over Gel Coat without Barrier Coat? - SailNet Community

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Old 04-23-2008
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Bottom paint over Gel Coat without Barrier Coat?

Hi all,

Here's a question which I'm sure may have been asked before: I spent last weekend trying to strip the old layers of bottom paint & barrier coat off my sailboat's 28' hull. What a job! I got to about 1/3 of the hull with a hook scraper when mu arms, shoulders & back ran out of strength. Some parts went right down to the gel coat where others went down to the barrier coat. My thinking is to sand everything smooth with an orbital sander, apply a few layers of anti-foul (no barrier coat) and put her in the (salt) water for the season. The gel coat, at least where I scraped down to it, appears to be sound. The intention would be to redo the hull in the fall when she's on the hard again. Would a season in the water have any detrimental effect on the gel coat if I do it this way?

Thanks,

John
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Old 04-23-2008
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I would say no, unless there is any evidence that the barrier coat is there as a result of a blister repair. If so, the blister problem may well return, and repairing new blisters later would be more trouble than restoring the barrier coat now. You should be able to tell whether there was a blister problem by inspecting those areas of gelcoat you can see - if they don't have patched divots you should not need to worry.

PS - don't remove any of the existing barrier coat if you can avoid it, you are jsut creating work for yourself to restore it.
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Old 04-23-2008
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I just finished that job last year, and you're going to love the results, in case you have any doubts.

I would paint it with the barrier coat now, rather than putting on antifouling and doing it next season. Stripping it is by far the hardest part, and, if you put on antifouling this year, you'll have to strip it again next year. It doesn't take that long to roll on the barrier coats, and then roll on the antifouling, and then you're done! It made me a little late to launch last year, but I got my sailing in by crewing for other folks. I'm just starting boat prep this year, and it'll be a snap.
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Thanks for the responses!

J
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Old 04-24-2008
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If Wag was going to put a barrier coat on, wouldn't he need to remove all the existing bottom paint first? I have been under the impression that barrier coat could not be applied on top of anti-fouling paint.
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Old 04-24-2008
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I'm curious. Could you sandblast the the bottom and the put on the barrier coat ?
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Old 04-24-2008
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Sandblasting can be a dangerous proposition as it can easily tear into the fiberglass lay-up quite easily and create more problems than it solves. Look into soda-blasting if you're looking for quick ways to strip. I have no personal experience with it, but I hear good things.
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I heard that sandblasting was a practice followed not too long ago but the more effective method these days is soda blasting - literally blasting the hull at high pressure with coarse baking soda. The cost seems to be around $40/ ft and the results are guaranteed. I spoke to a guy that told me that it would take a day for my 28' and that the hull would be stripped down to the gel coat by the time he was done.

J
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Old 04-24-2008
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Soda blasting is the preferred method these days, easier on the gel coat. I think waiting till the fall will do little or no harm to your boat, especially if you see little or no signs of blistering.

Yes, you must remove all the old bottom paints before applying a barrier coat. After having mine blasted I sanded it done smooth and removed any remaining bits of old paint.
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Old 04-24-2008
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Maybe I'm mistaken, but I thought you said you either scraped or sanded off all the antifouling, and that the only thing remaining is some of the barrier coat, which you are going to sand smooth at the edges. If so, I think you can apply barrier coat over it all, and then apply your antifouling. If all the antifouling is gone, you don't need to do any sand or soda blasting.

On a previous boat, I removed all antifouling from the keel, and left some of the old barrier coat, and added new barrier coat over the old, and it worked fine.
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