Proposal to Repair Deep Blisters

[Sonosailor]

I have developed deep golfball sized blisters on the stern inboard sides of the hulls of a 1996 FP Tobago 35, about a foot above the waterline.

As they typically shrink when the boat is out of the water, I have decided they are related to salt water osmosis rather than freshwater osmosis.

I ground them out until the pressurized yellow fluid squirted out, and am now letting them dry on the hard in Grenada. When I return, it is my intention to flood the areas with a low viscosity epoxy like "Git Rot" to try to block the path the osmosis is taking. I will let the epoxy cure, regrind a bit, then repair with marine polyester resin well wetted glass, so I can complete the repair with normal marine gel coat.

How do you see this working, and do you think there is a better way?

http://www.cruisersforum.com/forums/...1&d=1528290002

[chris95040]

Originally Posted by Sonosailor

I have developed deep golfball sized blisters on the stern inboard sides of the hulls of a 1996 FP Tobago 35, about a foot above the waterline.

As they typically shrink when the boat is out of the water, I have decided they are related to salt water osmosis rather than freshwater osmosis.

I ground them out until the pressurized yellow fluid squirted out, and am now letting them dry on the hard in Grenada. When I return, it is my intention to flood the areas with a low viscosity epoxy like "Git Rot" to try to block the path the osmosis is taking. I will let the epoxy cure, regrind a bit, then repair with marine polyester resin well wetted glass, so I can complete the repair with normal marine gel coat.

How do you see this working, and do you think there is a better way?

http://www.cruisersforum.com/forums/...1&d=1528290002

"Git rot" isn't a low viscosity epoxy, it's an epoxy mixed with loads of thinners.

(If anyone wants an actual low viscosity epoxy, I've used Progressive Epoxy Polymers "Low-V" before - its good stuff, and I think about 2/3rds the strength of regular epoxy.)

I don't think you want a thinned epoxy here - I believe the thinner gasses off and it makes the whole material more water permeable. I think you just want straight epoxy.

And gelcoat may not be what you want, either, since polyester's water permeability is probably what caused your problem in the first place.

Other folks who know a lot more about this issue will show up here with product recommendations etc I bet. But I think you want to wind up with a purpose-made epoxy "barrier coat" on top of whatever repair you do, then your antifouling on top of all that.

[Tortuga's Lie]

Is this localized or common through the hull? If it is localized, then repairing individually makes sense. If it is wide spread over the whole surface, you may want to explore the idea of peeling the bottom and re-glassing and then a heavy barrier coat.
Is this common to FP cats?

[Gafferfan]

Please note guys he mentions these are above the waterline.

[Tortuga's Lie]

Originally Posted by Gafferfan

Please note guys he mentions these are above the waterline.

Yup, missed that.........sorry. Might not want to peel in that case

[Greg Mason]

I have experienced blisters on 3 occasions on 2 different boats. Correct, 1 boat I treated twice. The apparent reason was, after the grinding process, the guy doing the fairing decided to use micro balloons in the epoxy to make sanding easier. NO BUENO. I believe a pure epoxy will be your friend in the long run. Pox above the waterline is not uncommon, right Uniflite? When I recently had my bottom soda blasted to remove all previous coatings, I sealed the entire bottom with Interprotect 2000 epoxy, even though there were no evidence of blisters at all. Good luck.

[Cadence]

Originally Posted by Sonosailor

I have developed deep golfball sized blisters on the stern inboard sides of the hulls of a 1996 FP Tobago 35, about a foot above the waterline.

As they typically shrink when the boat is out of the water, I have decided they are related to salt water osmosis rather than freshwater osmosis.

I ground them out until the pressurized yellow fluid squirted out, and am now letting them dry on the hard in Grenada. When I return, it is my intention to flood the areas with a low viscosity epoxy like "Git Rot" to try to block the path the osmosis is taking. I will let the epoxy cure, regrind a bit, then repair with marine polyester resin well wetted glass, so I can complete the repair with normal marine gel coat.

How do you see this working, and do you think there is a better way?

http://www.cruisersforum.com/forums/...1&d=1528290002

If you believe it is sea water osmosis, a foot above the waterlines, I'd be concerned where it is coming from, and if I read it right, why identical on both hulls. I almost sounds like repairing the result not the cause. JMHO

[psneeld]

usually you dont want polyester over epoxy.

I would fill if not too deep with a vinylester putty or Kitty Hair, then putty if deeper....only if above the waterline as you have said.

sand and gel coat to match.

I have done a decade of research on blistering and repairs since I ground off the bottom of my 40 foot trawler ....through the gel and matt into the roving due to severe hydrolysis ( the real issue and not blisters).

[Cheechako]

I have repaired deep blisters. First repair lasted maybe 1.5- 2 years. Really wet hull. The second time I ground them out and let them dry for 6 months until no sign of wetness (often there may be a dark ring in the blister.). Glassed the big deep ones. Used "kitty hair" on the medium ones. Just filled the small ones with marine bondo.
I think the real key was two thick coats of Epoxy resin after all was smooth and prior to bottom paint/primer. Real resin not barrier coat like Interlux. It was a distressing situation.

[Colin A]

If at all possible I would try and figure out how thew liquid got there. Lamination issue pinholes etc.

[fatherchronica]

Having done two extensive blister repairs on 36 footers I just wanted to chime in and say if, God forbid, I ever do another one I will use Progressive epoxies again. They are really easy to work with and the crazy guy who sells them swears if you ever get another blister it will indeed be from the bilge side. They can only ship by ground though, so may present a problem getting to Grenada. I wonder why they are a foot above the waterline though. Some weird sciencey thing no doubt.

[Squanderbucks]

The top coat with gel coat is fine but I would either do the repair with either vinyl ester resin or epoxy and glass whichever you prefer to work with. Vinyl ester is less expensive and cures fast so can be sanded and finished a little more quickly.

[Dave22q]

Strange situation. Above the water line rules out most well meaning advice. Normal blisters result from sea water intrusion, that is not what you have. Additionally blisters disappear within hours of being hauled.
Also 'deep' is a little vague. 1/8", 1/4" or what? Normal blisters cause arguments. I am in the camp that says they are self limiting and do not cause structural damage. Of course, many disagree to the delight of many yards.
However, I do not belive that what you have are blisters. I ould try to find a coatings expert for informed advice.

[chris95040]

Yeah i missed the fact that its above the waterline.

Thats weird, I’d want to root cause it.

[Suijin]

I'm fairly certain those are the result of uncured resin, not osmosis, given how far above the waterline they are. Are you sure they are shrinking when out of the water and it's not just an optical thing? Looking at them from the water, they are going to look bigger than when you're standing under the boat when it's hauled.

"stern inboard sides"...is that both sides? What do you mean by "inboard"...do you mean where the hull curves down to the waterline?

Polyester resin and gelcoat don't stick very well to epoxy. I would do it all with polyester, particularly if you want to finish with gelcoat.