Question about small blisters

Perithead · #1 (**permalink**) 03-26-2011

I just purchased a Montgomery 17 knowing that the bottom was 75% covered with blisters no larger than 1/8" in diameter and they are raised from the surface probably about the thickness of a sheet of writing paper or maybe a grunt more. I got a great deal on the boat so I am prepared to fix them if it is needed. The boat had been sitting in the water for 2 years, but it has been on the trailer now for probably 2 months or more.

I just got the boat home today and the first thing I did was take my key and try to burst open a few of the blisters to see how bad they were. When I would press on a blister with my key I would hear a very small cracking sound but I could not physically see any cracking being done and I could not see the blister "caving in". Also, no moisture was visibly present. I even scraped them a bit with my key trying to break them open but I couldn't get anything to come off.

My question is are these bad enough to need repairing? Cosmetically I do not mind the blisters at all, all I am really concerned about is the bottom paint adhering to them and not coming off.

I plan to paint the bottom with Pettit Vivid aintfouling bottom paint. If I didn't repair the blisters I would just scuff up the bottom with a sander then apply my paint.

So should I just paint it or fix them first? I am thinking just paint......

mitiempo · #2 (**permalink**) 03-26-2011

I don't think they are a big problem. Here's a link that explains gelcoat blisters very well. Sea Lake Yacht Sales (Kemah, TX)

centaursailor · #3 (**permalink**) 03-26-2011

Have a look at this http://www.cncphotoalbum.com/doityou...oat_repair.htm
I repaired some small clusters of blisters 6 years ago by poping them with a drill, washing and drying them out over the winter under cover and filling with International 2 part epoxy. Last years survey give me a clean report.

Yours are more wide spread so maybe leaveing them alone or stripping the whole gelcoat

are the choiceses.
Safe sailing

brokesailor · #4 (**permalink**) 03-26-2011

Wow those two articles contradict each other!

Perithead · #5 (**permalink**) 03-26-2011

Well, I guess I'll slap a coat of paint on the bottom and se what happens. If it fails, I am only out enough paint to paint the bottom on a 17' boat, not much....

Minnewaska · #6 (**permalink**) 03-26-2011

When faced with contradicting professional advice, I usually pick the one where I can afford to be wrong.

mitiempo · #7 (**permalink**) 03-26-2011

Blisters in the gelcoat and only the gelcoat are not a big problem, only cosmetic. If the blisters are in the laminate they are a problem. Blisters rarely go past the gelcoat. The article I linked to is by a very experienced surveyor. I have no idea where the second article came from as it is not even credited.

centaursailor · #8 (**permalink**) 03-26-2011

Quote:

Originally Posted by mitiempo

Blisters in the gelcoat and only the gelcoat are not a big problem, only cosmetic. If the blisters are in the laminate they are a problem. Blisters rarely go past the gelcoat. The article I linked to is by a very experienced surveyor. I have no idea where the second article came from as it is not even credited.

Ops, the article came off the C&C website.

C&C Yachts - C&C Photo Album & Resource Center

Of course its just an article, but does concur with a lot of the info I gathered before deciding what to do about my own hull blisters.

Safe sailing

mitiempo · #9 (**permalink**) 03-26-2011

There is an entire industry stripping off gelcoat and repairing the dreaded "osmosis". There are very expensive tools made and sold specifically for this. Fear is good for this as well as many industries.

Jan de Groot, a surveyor with decades of experience going back to the days before fiberglass has never seen gelcoat blisters progress past the mat layer just under the gelcoat and into the structural roving of a hull, nor one damaged in such a way as to be unsafe or unusable.
There have been issues such as the fire retardant resins used by Uniflite/Valiant referred to in the article (but not named) and that was a unique situation due to the additive used to make the resin fireproof. This problem was deeper than the gelcoat and existed throughout the laminate. Since fixed by the builder.
And the rare case of blistering that does go through the laminate because of contaminated fiberglass cloth/roving.

I have personally heard of many cases of blisters but none past the mat layer and into the structure. If there are a few, pop them, dry them, grind to get to the laminate but not past it and epoxy fill them, paint and you are good to go. If they are covering the whole hull removing the gelcoat and the mat below it is the answer to a good finish.
But don't live in fear of the hull falling apart because it just doesn't happen.

centaursailor · #10 (**permalink**) 03-26-2011

The question posed So should I just paint it or fix them first? I am thinking just paint...... didn,t give me the impression Perithead was living in fear.
Safe sailing