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Old 24-06-2013, 16:22   #31
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Re: Are barrier coatings bogus?

Jonathan, it sounds like you have been confused about the role of the different materials and products. Bottom paint serves only one purpose, to discourage critters and crud from growing on your hull. That's all.

Now, you're going to chew into your hull, removing at least portions of the gelcoat and frp and whatever resins (ployester, vinylester, epoxy, whatever) hold it together. I would suggest that you need something to replace the materials that you are going to strip off, because part of their job is to prevent water from migrating into and inbetween the layers and fibers in the frp material of the hull itself.

In theory the hull is one impervious block of plastic (frp) in practice, not quite. Layers are not always fully saturated or fully bonded. Resins are not always fully cured, leaving voids. How much of what is the problem is still debated--but the point is that there needs to be an outer waterproof "skin" on the hull if you want to be CERTAIN that moisture ingress won't ever be a problem.

Anything less is simply gambling, and if you want to gamble on a boat, go to Hong Kong or Macao, I understand the floating casinos are marvelous.

So whether you apply an epoxy coat that you chose or blend yourself, or a purpose-built barrier coat that is already designed for that purpose, I would suggest you do apply a new waterproof "skin" over the hull before applying bottom paint. And check with the manufacturers of both, to make sure the paints (excuse me, "coatings") are compatible. If you call those guys on the phone and call their products "paint" they tend to get upset. Paint, $20/gallon. "Coatings" ? Oh, right, $400/gallon seems quite reasonable. (sigh)
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Old 28-06-2013, 20:31   #32
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Re: Are barrier coatings bogus?

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It seems no one knows the chemistry involved... oh they will give you long paragraphs of theory..... But no one seems to know why some 40 year old non barrier coated boats dont have any blisters, and others 10 years old have them. If your boat has blister history... take the safe route.
Plenty of people do know the answer. But as the majority of defects are of the realm, 'installer error', the best way is to change to a construction method which allows for precise control of ambient environment all the while reducing error by the labor. Therein lies the answer to your question. Unless you have an autoclave, the best method is vacuum bagging. See Mineret's thread.

It's not dark art although working in resin is an artform. Environmental control is important.
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Old 28-06-2013, 20:52   #33
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Re: Are barrier coatings bogus?

We put a barrier coat on our boat about 5 years ago. The boat had some osmotic blisters and the factory paid for the repairs. The hull wasn't badly affected but the rudders were. Anyway, after 5 years the barrier coat and treatment seems to have worked just fine.

FYI, the blisters occur in polyester resin hulls due to small pockets of incompletely cured resins. When mixed with water, these form the classic acidic osmosis blister. We found all of the blisters were in the chop strand / gelcoat interface. The actual structural layup was fine.

If the blisters aren't too frequent you can just spot treat them - peeling a hull is a real PITA. Grind out, wash them with fresh water a couple of times a day for about 3 weeks, and steam them. Heat, apparently, chemically alters the uncured resins and neutralizes them (see the Hotvac site as well). Finally, after the boat has sat another week or so they glass the blisters and apply the barrier coat.
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Old 28-06-2013, 20:54   #34
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Re: Are barrier coatings bogus?

the chemistry...

Actually when blisters first became a big topic, in the 80's as I recall, Amoco did some extensive research (they make/made and sell resins) and published the results in a series of full-page ads in the major sailing magazines.

The only mystery left is "Does anyone remember what this boat was built with?" and that's when "used boat" reviews become valuable, because owner comments will tell you whether any particular maker, model, or time period had a particular problem.

But brokers aren't going to collect or show that information. After all, it would compromise their stonewall "I know nothing!" policy.
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Old 29-06-2013, 10:53   #35
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Re: Are barrier coatings bogus?

I probably mis-spoke, they know the chemistry involved when they analyze a failed layup, but I dont believe anyone has figured out why one boat blisters terribly and another doesnt... from the same factory. It seems to have historically been a thing that can happen to the most expensive boat or the least expensive. So far autoclaving and or vacum bagging is announced to help... but is there an science behind that assumption?
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Old 29-06-2013, 11:36   #36
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Re: Are barrier coatings bogus?

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I probably mis-spoke, they know the chemistry involved when they analyze a failed layup, but I dont believe anyone has figured out why one boat blisters terribly and another doesnt... from the same factory. It seems to have historically been a thing that can happen to the most expensive boat or the least expensive. So far autoclaving and or vacum bagging is announced to help... but is there an science behind that assumption?


Summer/winter boats make a huge difference. Winter boats are always better. Unless built in a fully climate controlled facility, which is still quite rare. Always amazed when people are surprised by poor quality coming from hot places like Florida, they're laminating in very high temps. Add a chopper gun to the mix and you've got a certain recipe for blisters, especially if its external mix.
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Old 29-06-2013, 15:00   #37
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Re: Are barrier coatings bogus?

cheechako-
"but I dont believe anyone has figured out why one boat blisters terribly and another doesnt... "
Yah, Amoco nailed that one in the 80's or early 90's. And I'm telling you, they printed the results. Whether any of that made it onto the internet afterwards...don't know. But there's no mystery as to why one boat blisters and a second one doesn't.

You may recall people would say "Don't buy a car built on Friday or Monday" because on Friday the guys were rushing to leave, and on Monday they were still hung over. Matter of fact, I know a Pearson that seemed to have built in a similar manner, we figure on Monday someone came back to work and said "Wow, look at that, did we finish all that on Friday?"

You mix the resin a little wrong, the temperature and humidity goes off, someone doesn't clean one roll of cloth or wet it out fully...this is like asking why two different gardeners or tailors do a different job. No mystery there at all, it is NOT Mr. Colt's interchangeable parts factory.

Vacuum bagging probably helps because it ensures a more even wet-out. 100% if done correctly, neither more nor less. And if you go to prepreg, where the cloth is pre-impregnated in a controlled factory...well kaching, but you remove more chances for human error. Remember, in the 70's and 80's it was a rare workplace that did alcohol or drug testing too.
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Old 29-06-2013, 15:06   #38
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Re: Are barrier coatings bogus?

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Remember, in the 70's and 80's it was a rare workplace that did alcohol or drug testing too.



Lol! It still is. Eliminate every boat builder or laminator who does drugs, and you're left with-not much! Sometimes I tell people that if you want someone to put on Tyvek and fullface and grind on a boat that's NOT theirs, it really helps if they are high when you try to talk them into that! The stories I could tell about the many characters I've met in the boat building industry, bottom to very top...
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Old 29-06-2013, 15:15   #39
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Polyester resin dissolves in water. A poor resin dissolves faster. When water mixes with polyester a larger molecule is formed by the interaction causing pressure . The reaction will blister if the outer coat/screen is fine enough. Not allowing the expansion to just press through. Like blowing up a bottle of vinegar and soda. If the bottle has holes the combination will just blow out if its restrained it will push at the outer wall. Your resin can dissolve and not form a blister.
I prefer using vinyl ester as a barrier over epoxy. I think it stays more flexible then epoxy. It builds out nicely. Cures faster. A compatible vinyl ester filler works great for fairing.
Hope that helps.
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Old 29-06-2013, 15:21   #40
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Re: Are barrier coatings bogus?

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Polyester resin dissolves in water. A poor resin dissolves faster. When water mixes with polyester a larger molecule is formed by the interaction causing pressure . The reaction will blister if the outer coat/screen is fine enough. Not allowing the expansion to just press through. Like blowing up a bottle of vinegar and soda. If the bottle has holes the combination will just blow out if its restrained it will push at the outer wall. Your resin can dissolve and not form a blister.
I prefer using vinyl ester as a barrier over epoxy. I think it stays more flexible then epoxy. It builds out nicely. Cures faster. A compatible vinyl ester filler works great for fairing.
Hope that helps.


We did many vinylester (Duratec) bottoms back in the old days before 2000. Not anywhere near as simple and easy, and we quit doing it because of recurrent warranty work. Some blisters always came back in vinylester, no matter how well dried. It just can't compare to the combination of 100% solids epoxy fairing combined with modified epoxy barrier coats like 2000e. Much faster and easier to do with vastly superior results.
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Old 29-06-2013, 15:38   #41
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Has it been that long. I recant and give way to minaret. Modern epoxy is the way to go. With caveat that you cut out the crap damaged stuff and are going onto something dry. Maybe that has changed too? Was my simplistic description good enough to satisfy the we don't know why blisters occur?
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Old 29-06-2013, 15:45   #42
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Re: Are barrier coatings bogus?

" just can't compare to the combination of 100% solids epoxy fairing combined with modified epoxy barrier coats like 2000e."

Makes sense. If the fairing is made from epoxy & nonabsorbant filler powder then you have essentially a thick barrier coat. Then it doesn't matter the solvent content of 2000e & tie coats as you already have it. Must admit the "barrier" coats from international & others are pretty nice to use.
Dunno if anyone remembers the test done on balsa cubes many yrs ago now by Gougeon bros regarding permeability of resins thinned with solvent. Pretty telling.
Everything is permeable with water vapour, just to different degrees.
This is old, but seems to have been rehashed.
http://www.westsystem.com.au/west_sy..._effectiveness
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Old 29-06-2013, 15:49   #43
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Re: Are barrier coatings bogus?

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Polyester resin dissolves in water. A poor resin dissolves faster. When water mixes with polyester a larger molecule is formed by the interaction causing pressure . The reaction will blister if the outer coat/screen is fine enough. Not allowing the expansion to just press through. Like blowing up a bottle of vinegar and soda. If the bottle has holes the combination will just blow out if its restrained it will push at the outer wall. Your resin can dissolve and not form a blister.
..........
This and the "Amoco solved the problem in the 70's" have been repeated many times... my point is, regardless.... boats keep blistering! so are these really correct data? Do builders just ignore the data? or what... Is it humidity? bad mixing? timing? How long was the cloth exposed to air? (if you put humid cloth into the vacum bagged unit, it's just trapping the moisture in...) etc. My guess is there are so many variables that the only way to really solve it is to do it as NASA would, in a environmentally controlled clean room....
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Old 29-06-2013, 15:58   #44
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We're back to bad lay up and the complex cure if resins. It's expensive to get all the pieces right. Humidity, temperature, resin ratio, proper integration between laminates. Blistering use the only issue. Adhesion can be big. When things go wrong in a layup it can sometimes be fixed without scrapping the hull. It might mean hot coating etc. been there done that even then it does not mean its a bad layup. So who knows. And then while most are craftsmen there is a tendency for the workers to have some issues. Watched one guy buff his shadow he was like ohhh yeah that's why it wouldn't clean up. Another guy fell asleep with a 16 grit porter cable grinder in his chest. Ehhh still running.
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Old 29-06-2013, 16:26   #45
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Talking Re: Are barrier coatings bogus?

The original MEE test was done in the late '90's & I do rememember that results for 100 microns of pure epoxy weren't much different from the thinned epoxy. The water exclusion went up exponentially from there with thickness.

Agreed, Sabray, all of the above. (Didn't see ur post)
The number of variables involved in production polyester manufacture is endless, from
temperature/humidity, gelcoat cure time to layup, to workers sweating into the layup, to the very chemistry of MEKP being a catayst as opposed the reactant hardener in epoxy. Cobalt bombs, Dma accelerators.....sorry not Mda.
Been there, migrated to epoxy.
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