Blisters-Sand Washing-What Now? - SailNet Community

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  #1  
Old 03-16-2006
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Blisters-Sand Washing-What Now?

My 1982 Pearson had blisters last fall at haulout. The yard suggested 'sand washing'. After much research and even more scotch, I had them do it - (it looks like it was sand blasted to me).

The blisters are now small holes through which i can see the fiberglass underneath. I presume that much of the gelcoat is gone too.

I was going to gently grind the blister holes and epoxy them, then apply a few coats of 2000/2001 or similar barrier coat follwed by bottom paint.

But an article from http://www.dockwalk.com/issues/2003/...listers2.shtml
suggests alkyd-urethane-silicon blend, or a two-part marine polyurethane paint works as well, or better, than barrier coat.

The barrier coat, they say, slows but doesn't prevent, water from entering the fiberglass. It will, however, prevent the mix of water and fiberglass resin from exiting resulting in new blisters.

The marine paint, on the other hand, allows water to move into the fiberglass faster than barrier coat but interacts with the resin in the fiberglass to slow resin mixing with water which creates the larger molecule that can't escape and causes the blisters. I'll get blisters sooner but not as badly (I guess).

If I use barrier coat andhave excessive blistering this fall, I'll be starting over. If i use marine paint (maybe Easypoxy by Petit) and get blisters, I'll kick myself for not using barrier coat.

What would you do?

Max
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Old 03-16-2006
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Max,

Here is what I did with my 1988 Pearson last year. I ground out the blisters (about 3 dozen of them), filled them in with epoxy and filler, then I applied 6 coats of MAS epoxy over that. Once it cured, I applied one coat of black hard bottom paint (Pettit Trinidad) and then 2 coats of blue ablative paint (Pettit Ultima SR.) If I start seeing black through the blue paint, I know it's time to recoat. When the boat was hauled last fall, the bottom looked terrific.

The MAS epoxy is very resistant to water penetration, and also is easy to use.

You'll get lots of opinions on what is best to use for a barrier coat. The choice is yours of course.
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Old 03-16-2006
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Interlux Interprotect 200E pretty much owns the consumer market for bottom protection due to good product that is relatively easy to use. We used it andt and would use it again in a second. Find the product in the Product Guide on http://www.yachtpaint.com/usa/default.asp.

Everything you need to know is in the Guide or Paint System Advisor. This stuff is expensive, follow the instructions exactly, and use whatever primers or preparation they recommend, even though you may $100 a quart...Use their Watertite filler for the blister divots, I think its only $50 a can.

Its a good thing this stuff is easy to use, because the project in which you use it is a bear and can take days into weeks depending on how much preparation you need to do. You need to fill all wholes, fair joints and anything else to your level of expectation, prine the keel as needed, and then apply at least 4 if not 6-7 coats, each coat needing a day to dry.

I have not heard many complaints about the barrier coating, properly doen, not preventing blisters for years of service, unless the moisture is coming from the hull interior. You've got to keep the bilge completely dry...

Good luck.
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Old 03-16-2006
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Here's a great article, online here at SailNet by Don Casey:

http://www.sailnet.com/collections/a...eid=caseyd0036
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Old 03-16-2006
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A similar topic was also discussed here a few weeks ago -

Barrier coat
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Old 03-22-2006
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Thanks

Thanks for your input. Time now for more research.
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