blisters on the hull

[Captain Bucknut]

Originally Posted by Cadence

Maybe an irrelevant question. What is the cause of blisters? A bad lay-up with air entrapment? Bad resin? All resin isn't equal. Just curious since it seems some boats develop them and some don't, seemingly by the same builder. Barrier coat seems to be the thing. If it is just a film that the first soft grounding will scrape off?
As to repair. If they are into the roving it would seem a quick in and out won't cut it since water had wicked and needs to be removed.
Feel free to pick it apart.

From my understanding, blisters come from water osmosis in the gelcoat. Seems more prevelant to boats built prior to the 90's as to the type of gelcoat used. Boat US "Blisters might signal a major defect due to either inferior materials or poor techniques when the hull was built, but absent a blistering history with other boats from the same builder, you should be slow to draw such a dire conclusion. Blisters also occur because an inattentive worker may have failed to apply the gelcoat uniformly; because fluctuations in the mix from the resin sprayer may have created spots of soft gelcoat; because features in the mold may have induced thinner coverage; because the gelcoat may have been sanded to excess by the owner or yard; because chemical stripper may have been used on the bottom; because contaminants in the water may have attacked the gelcoat; or a dozen other reasons." That's a basic oversimplification, but covers the basics.

[Scout 30]

Originally Posted by Dave22q

As far as I can confirm, there has NEVER been a case of structural damage caused by blisters. Looks to me about much hysteria concerning what really is a cosmetic issue. If anybody have evidence that my research is wrong please provide the details here.n I do know that BoatUS has no issues with covering a boat with blistering noted on the survey.

You'd be right if this was a discussion about stains but it's not. All blisters are structural. Even if the gelcoat is the only thing compromised that's still structural because the gelcoat is an important part of the structure. Large blisters can cause delamination deep into the substrate. You may think that they don't need to be repaired but that does not make them cosmetic. And even if you were correct I wouldn't consider cosmetic issues lightly. They can have a significant effect on value.

[Cadence]

Originally Posted by Captain Bucknut

From my understanding, blisters come from water osmosis in the gelcoat. Seems more prevelant to boats built prior to the 90's as to the type of gelcoat used. Boat US "Blisters might signal a major defect due to either inferior materials or poor techniques when the hull was built, but absent a blistering history with other boats from the same builder, you should be slow to draw such a dire conclusion. Blisters also occur because an inattentive worker may have failed to apply the gelcoat uniformly; because fluctuations in the mix from the resin sprayer may have created spots of soft gelcoat; because features in the mold may have induced thinner coverage; because the gelcoat may have been sanded to excess by the owner or yard; because chemical stripper may have been used on the bottom; because contaminants in the water may have attacked the gelcoat; or a dozen other reasons." That's a basic oversimplification, but covers the basics.

I can't wonder if it is not related to going cheap on the type of resin? I'm just curious if there is a real reason. Possibly someone working, back in the days of yore, at a builder has the answer. For example isothalic resin doesn't leach MEK is it likely to be less susceptible to osmosis?

[JPA Cate]

Hi, bodan,

Do not believe anyone who tells you "all boats have blisters". It is simply, not true, and I have heard it said countless times, usually by someone who had something to gain. Not that they are necessarily the kiss of death, good treatment, and barrier coating are just extra costs, but like the guys are telling you, how many? how deep? how big?

Good luck with it. The Nauticats are much liked by some people. See minaret's thread: Nauticat 52 Re-Fit.

Ann

[Dockhand]

it's true, blisters are caused by water osmosis through the gel coat. Sail boat mfg used the cheaper polyester resin over the more costly vinylester resin. Power boat mfg used the vinylester resin and had less issues with blisters. As processes have improved over the years and as more sailboat mfg have changed over to vinylester resins, along with several mfg putting a epoxy barrier coat on right from the mfg has helped. Having some small blisters is not the problem if repaired correctly, it's with the size and how deep. The best way to see the number and size of the blisters is only when the boat is first pulled from the water as they start to dry up once pulled, so the boat needs to be seen right away.