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Hull blisters / Osmosis from the inside

The "to do" list on my 81' Merit 25 restoration project just got a little longer. I hauled the boat out two nights ago and was finally able to get a good look at the bottom. What I found were plenty of blisters. I found 30+ 1/4"-1/2" and too many smaller ones to count. There are large sections covered in small goose bumps as well as several blisters that have popped. This is all below the waterline.

After reading everything I could find on the subject my plan of action is popping and grinding out the larger ones, sanding the whole bottom to the fiberglass, and letting it dry out a month or two while I work on other things. Then barrier coat, primer, and paint.

This boat has been out of the water its entire life, either on a trailer or lift. It has never been in the water for an extended period of time and hasn't even been in the water at all in 10 years. This leads me to believe the moisture came from the inside since a lot of rain water leaks into it.

Should I place some fans inside the bilge area? Is there a way to evaluate the damage to the inside of the hull? Would damage to the laminate begin on the outside where the blisters are forming even though the water is coming from the inside? Large portions of the bilge are obviously inaccessible because of the floor. If it helps I believe this hull is plywood cored.
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Re: Hull blisters / Osmosis from the inside

Been there, twice:

Here's my writeup:

https://www.dropbox.com/s/buhf5szxpe...rs%21.doc?dl=0

I'd get down through the gel coat and have a look. (A planer with a sharp blade, breathing protection, and earplugs will go through the gelcoat with control and leave a smooth surface.) You will see a white bloom to fiberglass layup that has been water damaged. (There's a pix of this in the file.) You might also look at moisture detectors. They will tell you if you've let things dry enough.

My bet is that your decks ARE plywood cored, but that the hull is solid layup. You'll find out pretty quickly.
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Re: Hull blisters / Osmosis from the inside

Thanks for the write up. I'm really hoping it doesn't go that deep into the laminate.
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Re: Hull blisters / Osmosis from the inside

Make sure you wash the hull with hot water several times after you peel the jellcoat. The chemicals inside the hull should be washed away, if not even a small amount of water will cause osmosis again. Wash with hot water, wait a week to dry, wash again, wait a week, wash again, check moisture content after a week, if still humid continue washing. The repair for osmosis is not covering with barrier coat but getting rid of the chemicals.
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Re: Hull blisters / Osmosis from the inside

If wishes can help, I'll add another. My first blister job was a Bristol 26. In that case, there was a poor bond between the gel coat and the layup, like they had shot the gel coat on a Friday and come back for the rest on Monday.


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Re: Hull blisters / Osmosis from the inside

Although I'm no expert on the subject , I have done a few blister jobs . First of all I'm not disagreeing with anybody here. IMO if your boat doesn't sit in the water for very long , then the blistering is caused from the initial lay up ( not uncommon ) not the water inside the hull . Your thoughts on grinding out and sanding I think are right . How else are you going to get the little guys without doing a full on peel job . OK I could be wrong on this but I would skip the barrier coat . I say after you dry out ( moisture gauge ? ) fill, fare, bottom paint . Yes I did leave out primer . It worked for me that way . My bottom job is over 5 yrs. old , prolly 2 yrs. past due . But although I'm bear in some spots no paint fell off and no new blisters . Yea ! By the way I used 3M Marine filler for the blisters and Z Spar for the paint .

3M Marine Filler 6 oz with Hardener - Star Marine Depot
Z SPAR Z-Spar The Protector | West Marine
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Re: Hull blisters / Osmosis from the inside

Why skip the barrier coat?

Ocean- that which covers 3/4 of a world made for man, who has no gills.
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Re: Hull blisters / Osmosis from the inside

Just curious, for those of you that have completely stripped the gelcoat, how long did it take you?

Additionally, I'm going to open up a few blisters this weekend to get a better idea of whats going on. What would I look for to determine if it was caused by a bad lay-up versus osmosis?

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Re: Hull blisters / Osmosis from the inside

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Originally Posted by seaner97 View Post
Why skip the barrier coat?
Good question . over 20 yrs. ago when we first got the boat it was covered with blisters . We hired the job out . It was very expensive , The guy used all the good stuff (Westsystem) and did what looked like a very thorough job complete with barrier coat . The blisters came back with in one yr. So we just lived with them in tell it got bad . Second time around I did the work (with Westsystem) I did not barrier coat and ground more of it off . Blisters came back but not as fast and not as many . This last time I ground more barrier coat and did the job as mentioned above . Like I said I'm no expert , It seems to me the barrier coat's absence Is not making any difference . IMO my blisters are coming from the lay up it's self and not from sea water penetration .

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Quote:
Originally Posted by Markwesti View Post
Quote:
Originally Posted by seaner97 View Post
Why skip the barrier coat?
Good question . over 20 yrs. ago when we first got the boat it was covered with blisters . We hired the job out . It was very expensive , The guy used all the good stuff (Westsystem) and did what looked like a very thorough job complete with barrier coat . The blisters came back with in one yr. So we just lived with them in tell it got bad . Second time around I did the work (with Westsystem) I did not barrier coat and ground more of it off . Blisters came back but not as fast and not as many . This last time I ground more barrier coat and did the job as mentioned above . Like I said I'm no expert , It seems to me the barrier coat's absence Is not making any difference . IMO my blisters are coming from the lay up it's self and not from sea water penetration .
Not uncommon from what I've read about them. Other than obviously draining water on popping them, I've never read about a sure way to tell the difference. Luckily, I've never had to deal with them. Anyone else?
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