Is this TRUE?.....Gelcoat blistering!!

[D. Stump, Hanalei]

I was recently talking to an old sailor here at work, and he said that gelcoat blisters are not always visible through the bottom paint. He said that if you scraped off the bottom paint and lightly sanded the gelcoat you would see small "pimples" that are the start of blistering. He also said that if you lightly sand just the bottom paint and see white dots in contrast to the brown bottom paint, then the hull is blistered. Is any of this true? When I bought Hanalei last spring, she had been on the "hard" for two years. I ran my bare hand over the entire bottom and detected NO blisters. Does that mean that Hanalei has no blisters? Her bottom feels as smooth as a baby's butt, and other than a little growth on her this fall when she came out, she seems just fine! I've never heard of this explanation of blistering before, what think you all???

Dave Stump
Captain Commanding
s/v Hanalei (CD-30)

[Dana]

I was recently talking to an old sailor here at work, and he said that gelcoat blisters are not always visible through the bottom paint. He said that if you scraped off the bottom paint and lightly sanded the gelcoat you would see small "pimples" that are the start of blistering. He also said that if you lightly sand just the bottom paint and see white dots in contrast to the brown bottom paint, then the hull is blistered. Is any of this true? When I bought Hanalei last spring, she had been on the "hard" for two years. I ran my bare hand over the entire bottom and detected NO blisters. Does that mean that Hanalei has no blisters? Her bottom feels as smooth as a baby's butt, and other than a little growth on her this fall when she came out, she seems just fine! I've never heard of this explanation of blistering before, what think you all???

Dave Stump
Captain Commanding
s/v Hanalei (CD-30)

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Yes.......it is true that not all areas that may need repair are really apparent visually or by feel. But.....you may already know that when one does repair blisters which really stand out, one generally misses one or two visually apparent blisters in the process. Just human nature.

But it is a fact that minor or blisters which are just starting to appear may not be seen or felt easily against the back drop of bottom paint. But folks have noticed that when the bottom paint is sanded down even the very small blister high points get "buffed" by the sandpaper first and then stand out against the bottom paint. They may also note a discoloration in the gel coat.

But......I would not get excited over this. To add to his comment I will add.....you can have "wet" mat areas behind gel coat which does not have blisters in that immediate area. Also a blister can disappear (the problem really doesn't) over a layup. I have opened up blisters as soon as I find them or mark them so I can find them again in the spring. That blister could have a pin hole somewhere so it can weep out and dry out on you. The blister high area disappears.

This is where the moisture meter comes in. Rarely does the mat of the "wet" blister mat dry out. But honestly.....baby blisters generally grow up to be bigger more visable blisters. If you have not noticed these bigger blisters you are probably ok. You can not just sand away each year looking for them. An occasional moisture meter may be the best bet if you can not sleep.

My marina, York River Yacht Haven at Gloucester Point, VA (Chesapeake Bay)uses a special pneumatic pin hammer to locate the blister. The head of the hammer is actually made up of a number of small individual heads which pound against the hull. The thought is....that gel coat which is not solidly adhered or supported to the laminate such in the case of wet mat or visual blister will crack the gel in that spot. Then they go into those spots for the repairs. they just have to go over every inch of the bottom.



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