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Old 07-03-2011, 21:29   #1
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Join Date: Aug 2010
Location: Hervey Bay Australia
Boat: Beneteau Oceanis 40
Posts: 29
Gel Coat Blisters

I have some small blisters that I wish to treat when I take my yacht out to antifoul it. Blisters are about 30mm. What is the best way to go about it in the time I have? It will be out of the water for a couple of days.

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Old 08-03-2011, 03:38   #2
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Location: Philippines
Boat: S&S 40
Posts: 789
Re: Gel coat blisters

It depends how bad the blisters are and how many..osmosis is a pain to fix properly.
To do it right u need to dry out the underwater body. I use infrared heaters wich I place around the hull..the drying out process can take a few days depending on the moister contents in the lay up. use a moister meter to check. Next step is to remove the entire gel coat, grind out the blisters, fill with an epoxy filler sand everything smooth. Apply 2 coats of clear epoxy like West System and 2 coats of an epoxy 2 pack primer..Epinamel made by Wattyl is a good choice.
If the osmosis is realy bad the underwater body has to be reglassed with glass/epoxy or Vinyl Ester.
Big job

If u just grind out the blisters and don't dry out the substrate it wont last.

Water molecules are in the lay up and were introduced when the hull was laminated and the humididty was not controlled.

The gel coat acts as a membrane..hence osmoses

Good luck
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Old 08-03-2011, 20:43   #3
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Join Date: Oct 2007
Location: San Antonio, TX/Bocas del Toro, Panama
Boat: 1990 Macintosh 47, "Merlin"
Posts: 2,761
Re: Gel coat blisters

I'm going to relate what WE did. YMMV (Your Mileage May Vary), when we hauled 3 years ago. We had about two hundred blisters, from dime sized, to a couple that were the size of the palm of your hand. At our surveyor's recommendation, we had them ground out, filled, barrier coated, and then painted with 2 coats of Interlux Ultra. We don't believe we got every one. The boat was out of the water for less than a week. It's now 3 years later, and we need to do the bottom again. We have between 5 and 10 blisters to fix... I can deal with that.
Bill Streep
San Antonio, TX (but cruising)
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