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Old 12-10-2015, 16:19   #1
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Gelcoat Blisters above the water line.

I have my 77 Sabre 28 on-the-hard for the winter. The starboard site is loaded with pencil-eraser size blisters. I plan on stripping the bottom paint to check there, but I see no signs of blisters below the water line. When popping the blisters, they definitely have a vinegar smell. I know I need to take care of this, and I am looking for some advise....

In reading up on this, I can:

1. Use an electric gelcoat stripper to take it all off down to the fiberglass.
2. Sand the gelcoat removing the tops of the blisters.
3. Sand blast
4. Use a counter-sink and drill to remove the blister and any acid damaged fiberglass.

Any other techniques that I am missing?



After the blisters are opened up by any technique, I would wash and dry, fill with 2-coats of epoxy, fill and fair, then re-gelcoat.

Anybody been through this? Any do's - dont's? Comments appreciated.

Bob M
Sabre 28 #283
Massachusetts
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Old 13-10-2015, 08:21   #2
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Re: Gelcoat Blisters above the water line.

Before you do anything else, you should consider acquiring a good quality marine moisture meter to take readings on your hull. This will tell you if you have a moisture problem with potential hydrolysis. Is the hull cored or solid? Does the core extend below the waterline? Often when I see blisters above the waterline, it is related to saturated core.
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Old 13-10-2015, 11:59   #3
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Re: Gelcoat Blisters above the water line.

Min--good post. But this shows a solid glass hull.
SABRE 28: A Solid Pocket Cruiser
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Old 13-10-2015, 15:59   #4
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Re: Gelcoat Blisters above the water line.

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Originally Posted by Terra Nova View Post
Min--good post. But this shows a solid glass hull.
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Very good. We still need moisture readings to determine if it's a wet hull. If it is, it should be peeled and dried. Otherwise you are treating the symptoms, not the disease, and the symptoms are likely to return.
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Old 13-10-2015, 17:10   #5
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Re: Gelcoat Blisters above the water line.

Thanks.

I failed to mention that the boat was shrink wrapped for ~1 year. It did not get in the water summer 2015. Prior to shrink wrap the blister damage was maybe 2ft^2, after shrink wrap it's almost the whole starboard side. It's now back at my house opened and drying. Minaret..... by "peeling" you mean the router-like carbide cutter that removes only the layer of get coat? I will get the moisture meter... Any manufactures better than another?

Thanks again,

Bob
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Old 13-10-2015, 17:46   #6
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Re: Gelcoat Blisters above the water line.

Quote:
Originally Posted by rmilk View Post
Thanks.

I failed to mention that the boat was shrink wrapped for ~1 year. It did not get in the water summer 2015. Prior to shrink wrap the blister damage was maybe 2ft^2, after shrink wrap it's almost the whole starboard side. It's now back at my house opened and drying. Minaret..... by "peeling" you mean the router-like carbide cutter that removes only the layer of get coat? I will get the moisture meter... Any manufactures better than another?

Thanks again,

Bob

I prefer the GRP-33. A Tramex is fine too. Are we talking Gelcoat or paint? Just need to know you are certain it's gel. How deep are the blisters?
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Old 13-10-2015, 19:20   #7
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Re: Gelcoat Blisters above the water line.

Not 100% sure it's gel. Just a guess at this point. Any sure-fire way to tell?

I will order the meter.

Thanks

Bob
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Old 13-10-2015, 19:25   #8
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Re: Gelcoat Blisters above the water line.

Quote:
Originally Posted by rmilk View Post
Not 100% sure it's gel. Just a guess at this point. Any sure-fire way to tell?

I will order the meter.

Thanks

Bob
Paint is extremely thin compared to gelcoat which is one way you can tell.

If the popped blister smells like vinegar it's probably in the gelcoat. The smell comes from the binders that held the fibers together dissolving in water.
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Old 17-10-2015, 10:17   #9
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Re: Gelcoat Blisters above the water line.

Moisture meter arrived, a GRP-33. Bought from Jamestown Distributors in RI, paid $351 without shipping. Ouch! But it's a great instrument, easy to use, and hopefully will last for years and steer me clear of bad boats in the future.

Anyhow. I took all of the readings inside. I'm in New England, so the air has been cool and dry, the boat has had a fan running inside 24/7 for a week, and has had the hatches opened when not raining.

The readings directly behind the blistering on the starboard are from 6-9 and similar around the entire hull except for the bilge where they reach 11.

I've used a chisel to chip away some gel/paint down to the glass to get a thickness, and I would estimate 1/16"+. Picture attached, and I tried to get the chisel tip and a finger in there for prospective.

Thanks

Bob
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Old 17-10-2015, 11:54   #10
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Re: Gelcoat Blisters above the water line.

Quote:
Originally Posted by rmilk View Post
Moisture meter arrived, a GRP-33. Bought from Jamestown Distributors in RI, paid $351 without shipping. Ouch! But it's a great instrument, easy to use, and hopefully will last for years and steer me clear of bad boats in the future.

Anyhow. I took all of the readings inside. I'm in New England, so the air has been cool and dry, the boat has had a fan running inside 24/7 for a week, and has had the hatches opened when not raining.

The readings directly behind the blistering on the starboard are from 6-9 and similar around the entire hull except for the bilge where they reach 11.

I've used a chisel to chip away some gel/paint down to the glass to get a thickness, and I would estimate 1/16"+. Picture attached, and I tried to get the chisel tip and a finger in there for prospective.

Thanks

Bob

Those are nice low readings, very good news for you. Question is, if it's dry, why the blisters? I'd say it's time for a small exploratory grind. Grind back to bare glass in a small spot with blisters. You'll probably find a matt layup with lots of pinhole voids underneath. Regardless, it'll definitely help you figure out what's going on. Congrats on a dry hull, and the GRP will serve you well if you take care of it. They are delicate.
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Old 17-10-2015, 12:17   #11
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Re: Gelcoat Blisters above the water line.

What did you think of the photo? Gelcoat?


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Old 22-10-2015, 15:30   #12
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Re: Gelcoat Blisters above the water line.

Did the test grind.... photos attached....

Definitely found a pocket in the gelcoat, but could not find a pinhole in the fiberglass. Could the moisture have gone outside in? So any water caught between the shrinkwrap and the gelcoat goes from outside in through imperfections in the gel and gathers there?

The attached photos were taken with an extra 10x eye-loop.

Bob
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Old 22-10-2015, 15:40   #13
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Re: Gelcoat Blisters above the water line.

The problem is resolution will require repainting the boat. It appears like you have a gel or paint issue and not much in the glass. That's a good thing, but one has to think about if the fix is worth it? It may be a $10k paint job on a 10K value boat.....
Maybe with old pourous gelcoat and shrink wrap the moisture was held in contact with the gel coat. or maybe the layup bond wasn't that good to start between the gel and glass, and sitting under shrink wrap, freeze or sun made them expand and pop out.
I've heard of issues with shrink wrap before.
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Old 23-10-2015, 04:42   #14
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Re: Gelcoat Blisters above the water line.

Quote:
Originally Posted by minaret View Post
....... You'll probably find a matt layup with lots of pinhole voids underneath. Regardless, it'll definitely help you figure out what's going on. .....
If that is the case and you are where it freezes in winter, moisture can enter and condense, then freeze which will expand and more water ..... Water and freeze/thaw cycling can cause extensive damage. A tight shrink wrapped boat would exacerbate the problem.

I had / have that problem with my teak overplayed deck and many other areas of our boat. Good luck
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Old 23-10-2015, 08:47   #15
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Re: Gelcoat Blisters above the water line.

Quote:
Originally Posted by rmilk View Post
Did the test grind.... photos attached....

Definitely found a pocket in the gelcoat, but could not find a pinhole in the fiberglass. Could the moisture have gone outside in? So any water caught between the shrinkwrap and the gelcoat goes from outside in through imperfections in the gel and gathers there?

The attached photos were taken with an extra 10x eye-loop.

Bob

Definitely gel, and a classic case of gelcoat pox. At least it won't need much dry time after peeling.
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