Blister Treatment

[galleyslave]

My 30 plus year old Vagabond has developed blisters under the antifouling. They appear to be forming between the glass/polyester body of the hull and the gelcoat. These are all being opened up, washed thoroughly to eliminate any traces of salt and they will have at least a month to dry in temperatures of around 35 degrees C. Most of the people I have spoken to mention epoxy based products like Gelshield and Gelshield plus to rebuild the damaged areas but I have just come across a poyester based material called GH 52008.

Does anyone have any experience of this product and would using this to fill the holes in the gelcoat and then use coal tar epoxy to seal the finish before antifouling be an advisable way to go.

Any comments and/or warnings gratefully received.

[Dynamo1181]

My experience on blister repair (3 boats) is that you are wasting youtime on the pop and fill technique unless you want a very temporary repair so the boat could be sold. A perminant repair would be to sand blast the gelcoat which opens the zillion blisters you have not detected and let the hull dry in a proper enviroment. The best solution is to peel the gelcoat off. With either method, an interlux 1000/2000 coating would then be applied.
I have doe it your way as well as the other two ways.
It all just comes down to money vs utility.
A

[boatman61]

I've done a couple of my own boats... one thing i'd suggest is as you start seeing the gelcoat through the remaining antifoul your sanding off... lighten the pressure.
You'll find little rings of antifoul appear... don't sand them out... they're all blisters and many you can't see with it sanded clean.. grind them back till the rings eliminated just to be sure of width... pressure hose well with FW then as you say, let her stand a while... one other thing I suggest is if she's in the open try and get her sat where she gets maximum possible sun/wind on all sides... N - S usually best else one side dries well.. the other.. well not quite... also may find you need to assist with heat drying from rear of keel to rudder where de sun don shine..
I've always used an epoxy/microballon mix followed by 3 coats of VCTar

[barnakiel]

In a light case (and with gelco or epoxy bottom) sand them off, dry, and fill with epoxy primer.

In a severe case strip the gelco, wash and dry, then follow up with epoxy system. This washing and drying takes time and a good place.

b.

[Zednotzee]

My $.02-

Hull Blisters: Know the Enemy

[joey69]

Fiberglass blisters occur because water passes through the gelcoat. Water soluble chemicals inside the laminate exert an osmotic pull on water outside, and some water molecules find a way through the gelcoat. As more water is attracted into the enclosed space, internal pressure builds. The water molecules aren't squirted back out the way they came in because they have combined with the attracting chemicals into a solution with a larger molecular structure. Instead, the pressure pushes the covering gelcoat into a dome-a blister.

For the rest.

[galleyslave]

Originally Posted by Zednotzee

My $.02-

Hull Blisters: Know the Enemy

That's a very interesting article. It appears to confirm my observation that the problem is at the interface between the gelcoat and the laminate but what I found particularly interesting (and surprising) is the note of scepticism sounded over the use of epoxies applied directly to the laminate.

[barnakiel]

I do not think the number is small. I can see blisters on most GRP boats that come on dry in our local boatyard, except the new ones. But 9/10 they are just blisters, not BLISTERS.

I have seen one of those Valiants with pox. Now those were BLISTERS - and they were everywhere - not just under the waterline.

b.