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Old 17-12-2012, 02:52   #1
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Osmosis question - I hope Minaret is listening!

Hi all,

After grinding and scraping off all the old anti foul and gel shield, we have more of an osmosis problem than I originally thought,
We have thousands of small blisters about 3 - 5 mm across, that have some fluid weeping out. I believe the blisters are just in the gel coat, but I'm just guessing

We are in Turkey at the moment, and don't have the time to dry the hull and do a proper fix.

Mt question is, should I recoat the hull with gel shield as I planned, or just put on a layer of primacon, then anti foul. Should I try to grind out the small blisters now?

We may be able to do a peel and hot vac in 12 months, or it might be 5 years, when we are back in Australia. The question really is, what's the best way to limit the spread of osmosis until we can properly treat it.

Thanks for any advice. Minaret, I hope you can chime in here.

Regards,

Steve
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Old 17-12-2012, 03:24   #2
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Re: Osmosis question - I hope Minaret is listening!

Hi Steve,
The first thing I would suggest is to talk to a local shipwright and just confirm that it is indeed osmossis and not something that needs to be repaired straight away (IE delamination which may cause structural issues - dont ask me how I know this ) If its confirmed as osmossis I would be inclined to repair the larger of the bubbles rather than the small ones. This is the method I have seen and been advised previously. There is a huge amount of information on osmossis on the net and I have yet to read an article of any boat sinking of osmossis.
There are a number of things that you do not state which are relevant such as when you first became aware of the blisters IE this haulout or previously. I would like to know what the construction of the hull is. If the hull is cored below the water line I would be inclined to get the work done as a priority as any water ingress into the core could end in a much larger bill or worse.
I live on Lake Macquarie in NSW and we own a 38 foot centre cockpit yacht moored on the Lake. There are many yachts out there that have substantial osmosis but it is accepted by the owners and they just repair the larger blisters each year and sail the rest of the season without worry.

Greg and Sue
Southerly Miss
Lake Macquarie NSW Aus
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Old 17-12-2012, 04:10   #3
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Re: Osmosis question - I hope Minaret is listening!

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Originally Posted by steve.garlick View Post
We have thousands of small blisters about 3 - 5 mm across, that have some fluid weeping out. I believe the blisters are just in the gel coat, but I'm just guessing
I may be wrong, but I don't think gelcoat itself weeps fluid.........

Quote:
We may be able to do a peel and hot vac in 12 months, or it might be 5 years, when we are back in Australia. The question really is, what's the best way to limit the spread of osmosis until we can properly treat it.

Thanks for any advice. Minaret, I hope you can chime in here.

Regards,

Steve
If it was 12 months then I would grind out and fill any voids, and leave anything else alone.

5 years? AFAIK, nothing makes osmosis "sleep" - except fixing by removing the problem completely ........likely won't be getting better in the meantime.

Of course the common "fix" is to grind out, fill and paint.......and repeat as required.
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Old 17-12-2012, 10:50   #4
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Re: Osmosis question - I hope Minaret is listening!

This sound like the pox, not actual blisters. They are caused by the porosity of gel coat allowing water thru, then the water hits the glass and starts dissolving small amounts of polyester resin. Frankly they are more of an unsightly and performance issue than any thing else. They do not grow over time, and tend to be pretty stable.

For a race boat it's a pretty important fix since they do slow you down, for a cruiser I would probably just let them deflate, then do a good barrier coat, and repaint. The truck with barrier coats though is you need at least 11mills of coverage everywhere, applied in at least three coats. Any less of either and you will have future problems.
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Old 17-12-2012, 10:54   #5
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Re: Osmosis question - I hope Minaret is listening!

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Originally Posted by Stumble View Post
This sound like the pox, not actual blisters. .

Isn't "the pox" osmosis?
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Old 17-12-2012, 11:03   #6
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Re: Osmosis question - I hope Minaret is listening!

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Isn't "the pox" osmosis?
Both certainly occur by e osmotic movement of water. But I generally think of pox as a very local very surface problem, and blisters as being a much larger problem that typically is caused by issues in the fiberglass resin, not just the permeability of the gel coat. They are caused buy the same mechanism though yes.
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Old 17-12-2012, 11:04   #7
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My understanding is that 'the pox' and blisters are both symptoms of hydrolysis. Water migrating into the laminate dissolves incomplete catalysts in the resin. This forms a highly concentrated solution in small voids in the laminate that encourages osmotic migration of more water into the laminate.

My question is not a general question about osmosis, but specifically, while awaiting a complete solution, is it better to barrier coat, and thus increase the " semi permeability" of the gel coat and hence raise osmotic pressure ( resulting in more blisters). Or should I leave the gel coat "open", reducing osmotic pressure, but increasing the underlying hydrolysis, and deeper laminate damage.

Can we focus the discussion around this, please.

Steve
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Old 17-12-2012, 16:18   #8
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Re: Osmosis question - I hope Minaret is listening!

I'll be around this evening, slaving in the yard right now. But I am listening...
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Old 17-12-2012, 16:24   #9
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Re: Osmosis question - I hope Minaret is listening!

Interprotect , whatever you do with the blisters, and do a properly peel off in a short future.....
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Old 17-12-2012, 16:37   #10
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Re: Osmosis question - I hope Minaret is listening!

More Mythology on "Osmosis" than anything else in boating. May I suggest
"Osmosis Mythology"
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Old 17-12-2012, 17:03   #11
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Quote:
Originally Posted by steve.garlick View Post
Hi all,

After grinding and scraping off all the old anti foul and gel shield, we have more of an osmosis problem than I originally thought,
We have thousands of small blisters about 3 - 5 mm across, that have some fluid weeping out. I believe the blisters are just in the gel coat, but I'm just guessing

We are in Turkey at the moment, and don't have the time to dry the hull and do a proper fix.

Mt question is, should I recoat the hull with gel shield as I planned, or just put on a layer of primacon, then anti foul. Should I try to grind out the small blisters now?

We may be able to do a peel and hot vac in 12 months, or it might be 5 years, when we are back in Australia. The question really is, what's the best way to limit the spread of osmosis until we can properly treat it.

Thanks for any advice. Minaret, I hope you can chime in here.

Regards,

Steve
My vote...

"Thousands" of blisters would concern me if it were my boat. However, time to fix properly is always an issue.

On my haulout I found "tens" of blisters. I point sanded them and have been letting them "air out for about 8 weeks. I will fill fair and coat. My hull is 31 years old and to be honest isn't worth the money of a peel job. I will manage the blisters until she ultimately dies as indicated by "real" delamination.

If your boat were mine I would point sand them and give them as much time to dry as possible. Job 2 is to stop as much water as possible getting in and that means a good barrier coat. Then top coat and plan the next haulout.

I would plan my next haulout (12-24 months) somewhere cheap where it can be peeled, dried and restored. Word to the wise - buy/rent/steal a peeler. Do not try a hand grinder - it is much harder/slower and you can make a real mess of it.
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Old 17-12-2012, 17:21   #12
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Re: Osmosis question - I hope Minaret is listening!

I'm not sure what gel shield is, but I'm assuming that the gelkote is still in tact. Getting a laminate profile might be a good thing to see exactly what is going on. However it's very important to get the hull dry as much as possible before putting on the barrier coat so barring that option, I would do the minimun amount as possible. I have blisters and the boat has been peeled and the real culprit is the Chopped strand mat that is between the gel and the first roven layer of glass. Much of that CSM as been removed where much of the blisters(voids) were located. The voids will be grounded out and interlux products used to fill and then barrier coated(many layers), but getting the hull dry is of upmost importance.
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Old 17-12-2012, 18:17   #13
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Re: Osmosis question - I hope Minaret is listening!

Hi all,
We had a similar problem with a Dehler 34 and it turned out to be the water barrier coating and not the glass. So we sand blasted the hull back to the gel which exposed some little glass imperfections as well. It was then faired and new water barrier coating applied. New antifoul and the whole job took tow weeks including removal of the rudder and reglassing to be sure.
Oz sailer had his job done at the same marina. It was a good result.
By the way the yard tried to sell me a new hull by saying it was ossie but a gring and a water test proved them wrong.
Derek
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Old 17-12-2012, 20:44   #14
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Re: Osmosis question - I hope Minaret is listening!

Quote:
Originally Posted by steve.garlick View Post
My understanding is that 'the pox' and blisters are both symptoms of hydrolysis. Water migrating into the laminate dissolves incomplete catalysts in the resin. This forms a highly concentrated solution in small voids in the laminate that encourages osmotic migration of more water into the laminate.

My question is not a general question about osmosis, but specifically, while awaiting a complete solution, is it better to barrier coat, and thus increase the " semi permeability" of the gel coat and hence raise osmotic pressure ( resulting in more blisters). Or should I leave the gel coat "open", reducing osmotic pressure, but increasing the underlying hydrolysis, and deeper laminate damage.

Can we focus the discussion around this, please.

Steve
An excellent question which I have encountered debate about before. I would be tempted to join the camp which suggests not barrier coating, thus sealing in the moisture already present, especially if you are planning on peeling in the near future. The added thickness of the barrier coat will make peeling more difficult. But the crux of the matter is really how much moisture is trapped and where. Gelcoat pox slowly becomes osmotic blisters which slowly become hydrolysis and delamination, as you know. The question is at what stage of that process is your boat? Only a combination of moisture meter readings and exploratory sanding/grinding will answer that question for you. It sounds from your description like classic gelcoat pox, but you can't be sure till you've ground a spot out. Get a sander with coarse disc and sand a 1' square all the way through the gel yourself. Stop regularly to look carefully at what is happening. Just doing this will tell you a great deal. Take pictures and post them here. Then get some good moisture meter measurements on the bare glass you have exposed, both immediately after sanding and after it's had some time to air dry. When you have done this you'll know a whole lot more about where you stand than you do now. I have attached a couple of pics of what classic gelcoat pox looks like as it is sanded. I'll scrounge around and see if I can find more pics or video that may be informative for you.

It sounds like a PO may have gone through exactly the same process and sealed up the gelcoat even though it was blistered. Or was the gel shield factory? I wouldn't expect so, or you probably wouldn't have blisters. You probably shouldn't make the same decision if you can avoid it, the longer it stays wet the further it will intrude into the laminate. Definitely do not spot grind and repair, this will create more problems than it solves in the vast majority of cases.
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Old 20-12-2012, 12:10   #15
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Re: Osmosis question - I hope Minaret is listening!

I'm planning to try Minaret's suggestion, an exploratory grind through the gel coat, but I'm having trouble locating a moisture meter in Turkey.

Here's some photo's of the current hull state, we've finished stripping her back. The green layer remaining we think is Primacon, we took off the alternating layers of Gel Shield (grey and green).
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