Hull Blisters, Treatment of [Master Thread]

[Prairie Schooner]

I feel like Christopher Kimball, Ericson's Test Kitchen. Funnily enough, the reason we stripped the bottom was what must have been at least 20 years of old paint chipping off in irregular chunks. The blisters were just a hiccup on the way.

 

[Pete the Cat]

My boat is out of the water having the bottom paint done here in SF Bay. We do it once every 3 or 4 years. This year was interesting. My boat is one that had a "blister job" done on it back a decade ago and we are now seeing the shortcomings of that effort. I have railed about folks not adequately drying out the hull and slapping a "barrier coat" (sounds really good and safe, doesn't it??) to protect the hull from future blisters. Boat owners will pay a lot of money for this "insurance". But I will just submit my vessel as another documentation of why this "preventive maintenance" is often (though not always) just kicking the can down the road and sometimes, just aggravating the problem. Someone at a well know boatyard here in presumably did a blister job on my 32-200 and slapped a barrier coat over their work. It probably reduced the number of blisters somewhat but each haulout I have a new crop coming up UNDER the barrier coat. You see (and I have done this with my Tartan 37) it IS possible to adequately dry out the hull, strip ALL of the gelcoat off the bottom, wait around for several months in a dry climate and reglass the whole bottom with a new barrier coat. The problem is, that this is generally not the way most folks, including my previous owner did things. They ground out the blisters, possibly got all the old bottom pain off and slapped on a "barrier coat" of several layers. Problem is that the hull is still wet and you will see blisters finding their way through because fiberglass laminate does wick water under pressure and it takes a long time to get it out. And few, if any boatyards, take the time to properly dry things out. I suggest that if someone suggests that you attack some blisters with a removal and filling and barrier coat that you defer from this effort unless the blisters are actively attacking the laminate--this almost never happens. Blister are, for the most part, just esthetic issues and have little to do with the structural integrity of the laminate or performance of the boat. I realize this is just an opinion, but it is the opinion of my most respected boattyard manager friends and a few competent surveyors. My point is apply barrier coats only over a a dry and well prepared surface or your result will look like my rudder. Picture attached. This what an improperly applied barrier coat does eventually. It is actually endangering, not protecting what is under it. FWIW.

 

[Drewm3i]

Interesting thread with a healthy dose of competing views!

I should add my $.02--and experience from my previous, 1987 E-38-200: like Pete's Tartan, Walden had hundreds of blisters, ranging in size from a fist to that of a (human) head, under (and/or within) a few layers of barrier coat, that had been applied about 5 or 6 years prior (this was in 2019).

Initially, we had thought the blisters proliferated because the yard applied the barrier coat over the pre-existing blisters without first fixing them, but after reading Pete's posts (in anticipation of purchasing another E-38-200), I'm not so sure. Since these blisters were so large--undoubtedly penetrating into the first layer or two of laminate in many cases--we ground all of them out and laid up new glass with various sizes of mat and epoxy. We then primed and painted with new ablative paint, without applying more barrier coat first.

Almost every time we ground a blister open, foul smelling resin-water slurry came shooting out. In most areas requiring repair, delamination was present--which required grinding out a wide and flat, large surface to apply new glass. After going through such an ordeal, I decided in the future, I would hire out bottom prep, i.e. sandblasting (since the job took so many months of almost daily work). All of this is to say, I would be a bit dubious about having an old boat with existing blister problems barrier-coated again; I think a bottom "peel" and re-glassing of the CSM layer (before barrier coat) could be different.

Some pictures: