Gelcoat Bubbling

A friend of mine stores his canoe in cotton bag outside of his house. We took it out yesterday for a run and when we unbagged the boat, we found a lot of small bubbles in the gelcoat. I've heard of this happens when something wet is allowed to sit on the canoe while the canoe is being stored like a wet foam seat.

Can anybody who has experience with working with gelcoat confirm:
1. is it caused by prolonged water exposure?
2. are the bubblest permanent?
3. is there a way to get rid of them short of sanding and reapplying gelcoat?
4. will it progress or will delamination occur if nothing is done to repair it?

Submitted by Snarfblat on Sun, 04/02/2006 - 6:51am

Read your comment that your friend that stores his canoe in a cotton bag. I too store my canoe in a cotton bag but out of the sun. I sure hope it's not the bag. If someone had their canoe bubble because of the bag please let me know and I will surely take it out. Thanks

#1 Sun, 04/02/2006 - 4:02pm

A friend of mine advised me to remove my seat from the canoe when its stored because the seat traps water between the seat and the canoe which causes bubbling. Despite the warning, I've never removed the seat and can say that I have not experienced any bubbling after two years of use. If prolonged water exposure causes bubbling in one boat but not another, there must be another factor that combines with the water to cause the bubbling.

#2 Mon, 04/03/2006 - 11:35pm

If your cotton hull cover is dry then it shouldn't cause any problems. Gelcoat blisters are frequently the result of water getting into voids between the laminate and gelcoat (could be a spider crack in the gelcoat or the laminate might not have been fully wetted during layup resulting in dry spots that water can permeate from inside the hull).

If the hull cover was trapping water against the hull so that the gelcoat couldn't dry off and there was a void then the cotton cover could have inadvertently cause the blisters.

The blisters can be fixed (unfortunately they won't go away on their own though) but you should probably check with your local builder (or a yacht repair place) on how to do it properly.

If you want more info check out this site (


#3 Wed, 04/05/2006 - 6:17am

Thanks for the link. The article was indepth and interesting

#4 Wed, 04/05/2006 - 9:13am

Hey. Remember my stingray did that? It looked like my boat had chicken pox. But when I took the seat off and let it dry the pox went away. Do you think there was moisture somewhere?

OK das all.

#5 Wed, 04/05/2006 - 5:32pm

Funny you said that (about drying). My friend and I paddled today. The goos bumps were gone. I could see small traces of the bumps from an angle but the bumps themselves are gone. Its kinda weird. I told my buddy to apply some car wax to help seal any micro pores in the gelcoat that may be causing the problem.

#6 Fri, 04/07/2006 - 12:36am

don't know how long the canoe has been stored like this but it could be osmosis.

it is common for polyester resin boats constantly in contact with water (fresh water is the worst) to absorb the water through the gelcoat. this appears as blisters which bleed water when popped.

when this happens, the only solution is to grind the gelcoat off back to the laminate layers and store in a completely moisture-free environment for 3 months or so before re-applying an epoxy gelcoat.

99% of polyester yachts built before 1990 experienced this

#7 Thu, 04/20/2006 - 5:58pm

Another good source on repair methods can be found at West Marine (see book at this link);

Skipper Rich

#8 Wed, 04/26/2006 - 8:25am

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