thousands of bottom blisters

[Sailing4Jesus]

Older GRP Hulls were built using the only Epoxy Catalyst that was available back then. Unfortunately, that Catalyst never stops hardening which gives of a gas that causes the Hull Blisters, meaning YES THE Blisters will return for the life of the boat, but its a Slow Process. Other than Pealing The Hull, (A Very Costly Endeavor) your best bet is as many here have already advised you. The Hull will probably need to be buried about Three Hundred Years from now, so sand it out as best as you can, then check with the engineers at AwlGrip as they will be your best source of whatever EPOXY PAINT you should Repaint the Hull with. Then do as all sailors do by Weighing Anchor, Setting Sails, and GO, GO, GO...

SEnior Chief, USN, RETIRED

[Cheechako]

Those tiny blisters aren't as bad as the big deep ones. I would just sand it enough to break open as many blisters as possible. Let it dry, the longer the better. All winter if it's stored. Then I would roll on two coats of real epoxy resin.

[geoff3nebel]

Here’s my two pennyworth: After I finally got round to removing several layers of old anti-fouling I found hundreds of tiny blisters - oh no... the dreaded boat pox! The surveyor took one look, chipped at a few... they were dry; had they smelled vinegary it would be expensive. He explained it was in the gelcoat and not structural. Apparently this occurs because the first spray of gelcoat into the mould has not been allowed to fully cure before the next coat is applied. It is not uncommon and does not threaten the integrity of the fibreglass layup. Depending on the size of the blisters it’s easy to fix. Mine were small - the largest maybe as big as my little finger nail and they were perhaps 1mm high. I sanded them flat and applied three coats of International Gelshield. The resultant finish looked like a new boat.

[boatpoker]

Originally Posted by Sailing4Jesus

Older GRP Hulls were built using the only Epoxy Catalyst that was available back then. Unfortunately, that Catalyst never stops hardening which gives of a gas that causes the Hull Blisters, meaning YES THE Blisters will return for the life of the boat,

SEnior Chief, USN, RETIRED

Epoxy resin in old boats is unheard of unless very high priced custom units. Til' this day epoxy resins are quite rare in production boats. Even so epoxy is not a "catalyst" system.I believe you are referring to the very common polyester resins with MEK catalysts which continually cure throughout their lifespan.

It is highly unlikely that blisters limited to the gelcoat will return if addressed properly, no peeling required for this cosmetic condition. Interlaminate blisters with hydrolysis are a whole different issue.

[Cadence]

Originally Posted by boatpoker

Epoxy resin in old boats is unheard of unless very high priced custom units. Til' this day epoxy resins are quite rare in production boats. Even so epoxy is not a "catalyst" system.I believe you are referring to the very common polyester resins with MEK catalysts which continually cure throughout their lifespan.

It is highly unlikely that blisters limited to the gelcoat will return if addressed properly, no peeling required for this cosmetic condition. Interlaminate blisters with hydrolysis are a whole different issue.

If he doesn't see glass fiber, which will wick, he is in good shape. Seal and paint. If some matt is seen no big deal. Some roving is another story if not wetted out but unlikely.

[Mike Banks]

Here is how I would go about getting rid of surface osmosis. Others may strongly disagree--but you only want to do this ONCE.

Clean off all of the paint down to clean fibreglass. If you have a really competent operator, you might be able to sand blast or plane it off, including gel coat, or you are going to have to suit up, mask on and do it with a vacuum-scavenging sanding machine. Such fun.

Use acetone to remove any possible tiny grease residues as well as helping to remove and surface or condensed moisture before painting.

When the hull is dry--use a hot air blower if you can get one and warm it up--use an epoxy primer coating to completely seal the hull. Use one with a bit of built-in keying capability such as one made by Wattyl to be used under their tough polyurethane finishes such as PolyU400. Only the very best will do here, and the epoxy primers should be put on thickly and not thinned.

However, epoxy primer coats once applied must be allowed to cure THOROUGHLY before any other paints are applied, and to this end a warm shed free of dust and moisture is ideal. A dehumidifier is a great asset. Many epoxies will absorb some tiny amounts of moisture vapour before fully curing, and anything that makes this a remote possibility has to be a good thing. Personally I would not do such a job outdoors--I would spend the extra money and hire a dry shed with a proper dehumidifier. This paint job is going to cost into the thousand by the time one has finished it--and spending the extra couple of hundred to get thirty or more good years is peanuts.

Now one other thing I might mention is the interior paint on the hull. Inside the hull of an older fibreglass vessel, the WORST thing you can do is to seal that surface fully by using an epoxy paint over it. That traps water inside, and these vapours reach incredibly high pressures, and as many as erupt on the interior surface of your hull will also appear on the exterior water plane surfaces. I suspect this may be something you need to check--and it does not have to be just epoxy paint that has this strong sealing effect trapping microscopic amounts of water, a good two-pack self-curing synthetic enamel could possibly cause it too.

[boatpoker]

Originally Posted by Mike Banks

Here is how I would go about getting rid of surface osmosis. Oth4ers may stroingly disagree--but you only want to do this ONCE.

Clean off all of the paint down to clean fibreglass. Sand blast or plane it off it if you have a really competent operator, or you are going to have to suit up and do it with a vacuum-scavenging sanding machine. Such fun.

Use acetone to remove any possible tiny grease residues as well as helping to remove and surface or condensed moisture.

When the hull is dry--use a hot air blower if you can get one and warm it up--use an epoxy primer coating to completely seal the hull. Use one such as one made by Wattyl to be used under their polyurethane finishes such as PolyU400. Only the very best will do here.and the epoxy primers should be put on thickly and not thinned.

However it must be allowed to cure THOROUGHLY and to this end a warm shed free of dust and moisture is ideal--because many epoxies will absorb some moisture vapour before fully curing, and anything that makes this a remote possibility has to be a good thing. Personally I would not do such a job outdoors--I would spend the extra money and hire a dry shed with a proper dehumidifier. This paint job is going to cost into the thousand by the time one has finished it--and spending the extra couple of hundred to get thirty or more good years is peanuts.

Now one other think I might mention is the interior paint on the hull. Inside the hulkl of an older fibreglass vessel, the WORST thing you can do is to seal that surface fully by using an epoxy paint over it. That traps water inside, and these vapours reach incredibly high pressures, and as many as erupt on the interior surface of your hull will also appear on the exterior water plane surfaces. I suspect this may be something you need to check--and it does not have to be just epoxy paint that has this strong sealing effect trapping microscopic amounts of water, a good two-pack self-curing synthetic enamel could possibly cause it too.

Mythology

[Corrosion-Eng]

Hi,
The CAUSE is stray current creating electrolysis. Current is flowing from your vessel via the water to the Earth. It can be stopped. Then the bubbles will stop. Google search for "how to stop stray current". Click on "How to prevent marine stray current".


There is a movie with before and after also photos on Fast Track.


Corrosion-Eng

[wingssail]

OK folks, stand by for some more sacrilege from the guy who NEVER seems to do anything like all the rest of you.

We've had our boat for 33 years. We haul out every year and do bottom paint, plus whatever repairs (keel etc) that are needed. We've sanded most of the paint off two or three times.

BLISTERS!

From day one we had blisters. First there were hundreds of them, as big as your thumbnail, and up to 1/8" deep, some deeper. We've always approached then the same way (out of ignorance and cheapness): We break them open with a pen knife, grind them out with a right angle grinder to the size of a quarter, fill them with WATEVER filler we have available, (remember we spent many years in the toolies where proper materials were not often available) then sand smooth, then BOTTOM PAINT!

No barrier coat, no primer, no long period for drying out, nothing. Just painted and splashed.

We never had time or money for the full monty bottom job; the boat is never stored for the winter (or here in Mexico, the summer) it is in use all year round, always has been. Bottom jobs are generally 5 days or less. The fastest, in Yambal was 24 hours. We're always in a hurry to save money or get to the next race or scheduled outing.

Granted our blisters never penetrated the laminate. They were not gel-coat blisters because our boat has no gel coat. They were limited to the paint and fairing compound used to fair the hull originally (knowing Tom Dryfus, I'm sure it was polyester body putty).

Over the years the numbers of blisters reduced. Last year we had maybe a dozen.

I could tell you a similar story about the lead keel which weeped water for years, was also repaired in a slapdash fashion (but I did use epoxy there) and gradually dried up. The rudder too. Never properly fixed. Now, no problems.

I have to feel sorry for the boat yard guys who might have missed a car payment by my cheapness in not hiring them, but, we all have to look out for ourselves.

If however, you really love your boat, and have the money, spend it (all of it) and do it right!

[boatpoker]

Originally Posted by Corrosion-Eng

Hi,
The CAUSE is stray current creating electrolysis. Current is flowing from your vessel via the water to the Earth. It can be stopped. Then the bubbles will stop. Google search for "how to stop stray current". Click on "How to prevent marine stray current".


There is a movie with before and after also photos on Fast Track.


Corrosion-Eng

As a Certified Marine Corrosion Analyst, this is the most bizzare, irrational nonsense I have read on this forum

[sailcrazy]

We had a similar issue on our 1989 boat some years ago. Every season we would haul out, attack and repair the numerous blisters that would pop, recoat and repaint, and go for another season. After several years of doing that, a local fiberglass expert overheard me talking about it, and suggested a fix that has held to this day. According to him, the gelcoat can "wear out". And when it does, you need to peel it off, refeather the hull, reseal it, and then repaint. We peeled the bottom and refeathered it, then applied 6-8 coats of 2-part resin, with a barrier coat mixed into the last 3-4 coats, and then let it all cure completely....it was a round the clock operation, appling the next coat when the previous coat was still tacky. After it cured completely, we sanded the blume off, applied another coat, then a primer, and then 2 coats of good antifoul. That was in 2008, and we have NOT had a blister since! His process worked. FWIW

[double u]

...“Older GRP Hulls were built using the only Epoxy Catalyst...“

...it would be great if people here would only impart knowledge, not just phantasies...

[bobnlesley]

There's some good advice here, but some bollox too; I'd advise simply picking the low cost/low effort answer that you like best and going with that. Then again you could take our approach which is to haul, clean and lightly sand/key the hull, then slap some new anti-foul paint on it and relaunch. From the photo your blisters look no worse, indeed probably less than ours and we just ignore them - it's a low cost/low effort approach and once you've relaunched you can't even see them, so they no longer exist.

[Tillsbury]

Originally Posted by boatpoker

As a Certified Marine Corrosion Analyst, this is the most bizzare, irrational nonsense I have read on this forum

Wow, boatpoker, I didn’t realise you were new here

[skipgundlach]

Originally Posted by geoff3nebel

Here’s my two pennyworth: After I finally got round to removing several layers of old anti-fouling I found hundreds of tiny blisters - oh no... the dreaded boat pox! The surveyor took one look, chipped at a few... they were dry; had they smelled vinegary it would be expensive. He explained it was in the gelcoat and not structural. Apparently this occurs because the first spray of gelcoat into the mould has not been allowed to fully cure before the next coat is applied. It is not uncommon and does not threaten the integrity of the fibreglass layup. Depending on the size of the blisters it’s easy to fix. Mine were small - the largest maybe as big as my little finger nail and they were perhaps 1mm high. I sanded them flat and applied three coats of International Gelshield. The resultant finish looked like a new boat.

I've read the thread as it is at 6AM east coast.

This is cool. No vinegary, no reddish liquid running out, likely it's not in the polyester layup. Good to go.

Actual fiberglass blisters is another story, and I saw many references to time, but none to removal of the cause, as to how to dry.

As it doesn't appear that fiberglass is involved, I'll spare you.

But if you want to dry out actual fiberglass blisters, see my story on our bottom job in 2011-12, along with pictures links, here on CF.

All that (our experience and the presumption of paint-only) said, if it's a low-dollar and old boat, obviously it's not sunk yet, and is unlikely to do so in the future. Fix the pox, put on paint, and head back out. I've not heard of blisters (even in fiberglass) sinking a boat, yet...