Author Topic: Barrier Coat?  (Read 1848 times)

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moonie5961

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Barrier Coat?
« on: 26 July, 2010, 01:21:03 »
Fellow Contest owners, advice is sought. I offer my apologies for not being able to pose this query in Dutch, hopefully it will translate alright.

I have recently stripped the bottom of my boat down to the original gelcoat. The previous owner applied an epoxy barrier coat, but did not properly prep the bottom. The epoxy was flaking off in enough places to justify its removal, and there were blisters present under the epoxy- which did not penetrate into the gelcoat. This leads me to believe that the previous owner did not let the hull properly dry before applying the epoxy barrier coat. The boat has been out of the water since last September, so the hull is as dry as it will get.

I am wondering whether I should apply another barrier coat, or if I should just paint anti-fouling over the gelcoat.

I am leaning towards the barrier coat, but am reluctant for several reasons.

First, the other barrier coat did not prevent blistering, so if this method has not worked before, I don't have much confidence that it will work this time.

Second, removing the failed barrier coat was so difficult, especially while trying to leave the gelcoat in tact. I feel that if I apply a barrier coat and it does not work as I'd like, I'm just creating more miserable work for myself later.  At least if I skip the barrier coat and get blisters, I don't have to remove an epoxy shield.

Third, I don't know how prevelant blistering is in Contest hulls. My boat was constructed in 1974, are Contests of this era known for blistering?


The case for going ahead with the barrier coat can be made as well.

First, the boat will be kept in the warm Gulf of Mexico, and warm water is a catalyst for blistering.

Second, the gelcoat is very thin in places. Some say that this is not a problem, as gelcoat is merely cosmetic, but others insist that gelcoat is integral in preventing water ingress into the laminate. I don't know which to believe.

Thirdly, the barrier coat was applied before, so that may indicate that this boat is indeed prone to blistering, or it could just be that the previous owner applied it as an attempt at pre-emptive measures against blistering.

What it comes down to is that I am really curious, do your Contests blister? Do you have a barrier coat?

I have read about some Contest owners going through great measures to prevent blisters, including heated vacuum contraptions, vinylester, etc., I'd just like to know whether a barrier coat in this instance is a good idea or not.

I have not found ANY blister which extends into the laminate, so there is no issue here of hydrolysis- I am just looking to do the right thing the first time, so I don't have to strip the bottom again!

Thanks, I hope that I explained myself clearly enough.



Offline BJ

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Re: Barrier Coat?
« Reply #1 on: 26 July, 2010, 09:21:43 »
Blistering .... hmm.. an issue which often leads to fanatical discussions between believers and non-believers... :D

Let's see.. you say: "The epoxy was flaking off in enough places to justify its removal, and there were blisters present under the epoxy- which did not penetrate into the gelcoat. This leads me to believe that the previous owner did not let the hull properly dry before applying the epoxy barrier coat."

I would say that if there are no blisters in the gelcoat or in the laminate, then the hull is dry and never had a problem in the first place. I'm not sure if moisture is the cause of the blistering of the epoxy, could also be bad prepwork or the wrong circumstances during application.
The matter of applying a new barrier coat is a though one. Imho, since your boat is already 36 years of age and the hull is still in good shape there would be no reason to do so. I mean any form of uncured rasin should be long gone by now so there's nog more danger of hydrolysis...  I guess it's more a state of mind: do you feel more confident with an extra cout then you should apply one. Make sure to prep the bottom in a proper way and make sure that you have te right temperature and hummidity etc when you apply it. Should be rather easy then.
Last time my boat was out of the water I didn't see any blistres, I don't have a barrier coat, I'm in the water year around and my boat was built in 1971.

And about Contest hulls: the old ones were build in a good old, hand-layup, better-safe-then-sorry way. They are known to be thick, heavy and strong... ;)   

Hope this helps a bit.

   

moonie5961

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Re: Barrier Coat?
« Reply #2 on: 27 July, 2010, 04:38:01 »
It does, thank you for taking the time to make such a great response!

I agree, the topic of blistesrs is definitely a polarizing one.

You offer some great advice; you're right- the boat has at least survived 36 years!
Like you said, I would probably feel better if I had an extra coat of epoxy, but I feel that's more a factor of human nature than real confidence in the epoxy system. I mean, it's always easier to feel confident when you've done something-regardless of whether that something was effective, or not. I feel like either way I choose, I'll probably end up kicking myself later.

If anyone is interested or does not mine lending an opinion, I'll link my photobucket album which shows the condition of my gelcoat. I'd really appreciate if anybody who is interested would take a look, and let me know what you think.
http://s789.photobucket.com/albums/yy180/moonie5961/?action=view&current=seagreen.jpg

Thanks again, BJ for the advice!!

maxbolweg

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Re: Barrier Coat?
« Reply #3 on: 27 July, 2010, 12:00:10 »
Gd,

As far I can see think epoxy barrier coat (gelshield) is to be recommended. Since it seems that gelcoat seems somehome damaged/porous. In this case laminate will be better protected.

My C33 had blisters after a previous treatment. Had a hotvac done and am to be considered as a believer   ;). After three seasons no blisters reoccured.

Fyg a friend  is planning to put gelshield/epoxy on his yacht without removing the original gelcoat. He has been advised to clean the gelcoat with fresh water every day for 1 week before putting the gelshield on it. The water would attract possible (acid??) pollution.

Best regards, Max
« Last Edit: 27 July, 2010, 20:12:31 by maxbolweg »

Offline BJ

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Re: Barrier Coat?
« Reply #4 on: 27 July, 2010, 13:13:58 »
"Fyg a friend of mine is planning to put gelshield/epoxy on his yacht without removing the original gelcoat. He has been advised to clean the gelcoat with fresh water every day for 1 week before putting the gelshield on it. The water would attract possible (acid??) pollution. "

If you can subtract pollution through the gelcoat then adding a barrier coat would not be nescacerry since the problem would solve itself: no acid (or other stuff) thus no hydrolysis and no blisters.  In other words: daily cleaning is pointless which says something about the man/woman who gave the advice.

maxbolweg

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Re: Barrier Coat?
« Reply #5 on: 27 July, 2010, 16:09:20 »

As far as I know we are talking about a cummulative process: 'water + GRP harder => 'acid' => acid attracts water etc'
Cleaning the vessel and keeping away the water by a better coating should help if you look at it this way, I think. The advise came I believe from the seller of the epoxy/gelshield. But what will they know...

Regards, Max

Offline BJ

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Re: Barrier Coat?
« Reply #6 on: 28 July, 2010, 09:31:51 »
Washing the outside of the gelcoat to get rid of the pollutions in the laminate is like washing the inside of a window to get rid of a stain on the outside: it won't work! If washing the outside would help then the whole blister-issue wouldn't exist because all the dirty stuff would be washed out during the sailing. So that advice simply doesn't make any sense to me....
Your equation is not completly incorrect except for one thing: it's not the harder that causes the problems but the uncured raisin. The raisin is hygrospocic (so it attracts water) _and_ it wil splt into its two basic components when water is added. That is called hydrolysis and that triggers the so called osmosis process. At itself nothing new, you can find this information on many websites of all the comanies who are selling you the epoxies and the osmosis-treatement.
However there is also some stuff that they don't tell you and that is the good news. First of all, there is normally not that much uncured polyester in the hulls so when that has alll been disolved the process stops. Second, uncured polyester doesn't add anything to the structural intergrity of the hull so if it disolves you won't loose any as well. Third, a 30 plus year hull that is still strong and shows no signs of serious delamination will live on te be a 100 years. And why don't they tell you this?? Well, they would be out of business in a week... ;)
But as I said earlier: if you sleep better with an extra barrier coat then add one. But also realize that it will not stop the hydrolosis, it will only prevent the occuring of blisters.

Offline BJ

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Re: Barrier Coat?
« Reply #7 on: 28 July, 2010, 13:39:45 »
Nice to read:  http://www.osmosisinfo.com/handb9a.pdf   The book on osmosis, hydrolosis etc. by the inventor of Hotvac, Bengt Blomberg. Explains a lot although I still disagree with him on some issues.

maxbolweg

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Re: Barrier Coat?
« Reply #8 on: 28 July, 2010, 16:15:54 »
hadie BJ,

Thanks for your extended explanation/corrections. I wrote in haste.
I was amazed by the advise of cleaning gelcoat myself also, but....

Anyway I know you are a non believer on (the danger/problem of) osmosis.
On the other hand the fact remains that gelcoat does not protect the laminate from water as much as epoxy and as a friend(same friend) says: epoxy weights less...
Suppose that instead of epoxy primocon could be used as a much easier/cheaper barrier coat/ protection also??

So when will you visit IJburg harbour??   
« Last Edit: 28 July, 2010, 16:19:06 by maxbolweg »

Offline BJ

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Re: Barrier Coat?
« Reply #9 on: 28 July, 2010, 16:58:17 »
Two other facts: first, epoxy does not protect the laminate as well as they make you believe and second, the laminate doesn't need that much protection unless it's a really bad one. Has nothing to do with believing or not and everything with good ol' physics... ;)

IJburg?? Don't know, haven't been sailing much lately. Will you attend our Enkhuizen CYOC-meeting in september ?

 


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