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Author Topic:   Blisters - Paint or Gelcoat?
montaukmax posted 06-02-2002 02:09 PM ET (US)   Profile for montaukmax   Send Email to montaukmax  
I have noticed a series of small blisters below the waterline at the bow of my 1974 Montauk/Nauset. The bottom is painted with bottom paint over an off-white undercoat. I am hoping the blisters are just in the paint layers. Anyone have advice on how to tell?

Thanks for any suggestions!

Soho posted 06-03-2002 09:00 AM ET (US)     Profile for Soho  Send Email to Soho     
I think that you need to have the boat out of the water for this one; once out you can prick one of the blisters and see what the composition of the blister is. It should be obvious if it is the paint blistering or the gel underneath. How big are they by the way ? I have never had bottom paint blister though... usually has been the gel underneath.



Boston Marine posted 06-04-2002 03:38 PM ET (US)     Profile for Boston Marine    
Chemical reactions take place between water absorbed by osmosis, and water soluble molecules in fiberglass-composite hull structures. This causes surface blistering of the gel coat. The blisters are usually below the waterline and will swell and contract due to temperature changes. If unchecked the bubbles will enlarge and hull deterioration will escalate as blisters open and admit even more water. Osmosis + Blistering = Hull Delamination
Quoted from Electrophysics in Ontario, Canada
JimU posted 06-05-2002 03:02 PM ET (US)     Profile for JimU  Send Email to JimU     
Take a sharp pointed knife and pop out one or two of the blisters. You'll be able to tell whether or not it goes into the gel coat. If you have gel coat blistering, go to the west system blister repain and prevention manual. Get the video on how to diagnose and repair. I used the sand blasting technique describe in the video but used baking soda as the blasting medium as I did not want to remove the entire gel coat in the blistered area. good luck. JIM
vinay posted 12-30-2006 10:20 PM ET (US)     Profile for vinay  Send Email to vinay     
It would have been useful to know if the craft is kept in water or on a traylor most of its life.
If in the water, than I don't think I would use 'typical paint' products under the water line. There are many reasonably prices epoxy or urathane product to fill the bill rather than thinner based paint. I would expand my research in hard epoxy antifouling.
if on a traylor, then it is cosmetic, Osmosis requires time AND moisture to establish itself

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