Osmosis a year after work

[Ron5]

My boat is in Lanzerote.

Last August (2015) it was taken out, the hull completely stripped, re-painted and antifouled.

Today it was taken out for cleaning and their is some osmosis on the hull. Is this to be expected or a job not done correctly?

Cheers, Ron

 

[macd]

Last August (2015) it was taken out, the hull completely stripped, re-painted and antifouled.

Today it was taken out for cleaning and their is some osmosis on the hull. Is this to be expected or a job not done correctly?

Do you mean the gel coat was stripped off?
What sort of drying regime was used?
What was it 're-painted' with? And do mean that it was painted before?
What are the inidications of osmosis now?

 

[Deleted member 36384]

There is a body of opinion that describes a technical position where a GRP laminate that has Osmosis or Hydrolosis as they refer to it, will rapidly develop blisters after a strip and epoxy repair. The information is available in the book Osmosis Handbook Edition 4 January 2000

It can be dowloaded free with the owners consent from here: http://www.osmosisinfo.com/handb9a.pdf The link to the pdf book is from this site http://www.osmosisinfo.com

 

[savageseadog]

I've always advocated popping the blisters on a yearly basis, making good with epoxy filler until it's sorted.

 

[longjohnsilver]

Was the gelcoat stripped? Was it then epoxied? We need those answers before a meaningful response can be given.

 

[jwilson]

If by "stripped" you mean just all the old antifouling taken off then this is common- possible all the old antifouling has been having some minor anti-osmosis protective effect, but more likely simply that blisters are far more obvious on a smooth hull.

 

[Colvic Watson]

If by "stripped" you mean just all the old antifouling taken off then this is common- possible all the old antifouling has been having some minor anti-osmosis protective effect, but more likely simply that blisters are far more obvious on a smooth hull.

+1

 

[Davegriff]

Last August (2015) it was taken out, the hull completely stripped, re-painted and antifouled.

Are you sure it is osmosis, and not just paint blisters from a bad paint job?

 

[Ron5]

Thanks very much for the replies. I am a novice at this so please bear with me.

The boat, a 2000 42 Bavaria had an extensive survey in July 2014 and their was no sign of osmosis. Their was a recommendation that the old anti fouling be removed and re applied. In August 2015 the boat was taken out to do this. The boatyard stated:

Bottom paint: in order to get off all the antifouling we will have to use a product, paint stripper.
After using this paint stripper the boat will have to sand the hull, paint with a primer, in this case Gelshield 200 (International) and then the antifouling. This was done in Lanzerote over a four week period in August.

The osmosis was present when hauled out this week.

Cheers, Ron

 

[dombuckley]

What size are the blisters and how deep do they go?

Open one up: I would lay good money that the blistering is actually amine sweating of the gelshield, and not within the gelcoat or the structural laminate.

 

[Deleted member 36384]

Ron,

My post #3 is not relevant in this case. As others have said it is likely to paint blisters or the gelshield. You hull is likely to have been constructed such that Osmosis is very unlikely.

 

[macd]

What size are the blisters and how deep do they go?

Open one up: I would lay good money that the blistering is actually amine sweating of the gelshield, and not within the gelcoat or the structural laminate.

I think that's quite likely the cause. Certainly Ron ought to open some of the blisters to see precisely between which of the hull layers they lie: lay-up; gelcoat; gelshield; antifoul.
Isn't Gelshield 200 a solvent-based epoxy? Presumably overcoating before the minimum overcoating time is reached could give solvent-entrapment problems?

 

[Ron5]

I think that's quite likely the cause. Certainly Ron ought to open some of the blisters to see precisely between which of the hull layers they lie: lay-up; gelcoat; gelshield; antifoul.
Isn't Gelshield 200 a solvent-based epoxy? Presumably overcoating before the minimum overcoating time is reached could give solvent-entrapment problems?

Thanks again for the replies. I used the information them plus other information and went back to the boatyard who are pulling the boat today, leaving it to dry over the weekend and investigating on Monday.

I will post on here the outcome, it should be interesting.

Cheers, Ron

 

[Pasarell]

What size are the blisters and how deep do they go?

Open one up: I would lay good money that the blistering is actually amine sweating of the gelshield, and not within the gelcoat or the structural laminate.

Gelshield 200 is the solvent based version so unlikely to have suffered from amine sweat.
Solvent entrapment is quite possible if overcoating times / temperatures not followed properly. Other thing to look at is how the surface was prepared and how many coats applied.
If surface preparation not good enough then blisters between epoxy and gelcoat are very likely. If dry film of Gelshield is not enough then osmosis between it and gelcoat is very likely indeed, and even more so if preparation of gelcoat not good enough.
Chances of osmosis in a boat of that age are low but the other thing to look at is if the gelcoat was damaged during stripping the old antifouling. If that happened then solvent from Gelshield could penetrate to the laminate and cause osmosis to start

 

[eddystone]

Gelshield 200 is the solvent based version so unlikely to have suffered from amine sweat.
Solvent entrapment is quite possible if overcoating times / temperatures not followed properly. Other thing to look at is how the surface was prepared and how many coats applied.
If surface preparation not good enough then blisters between epoxy and gelcoat are very likely. If dry film of Gelshield is not enough then osmosis between it and gelcoat is very likely indeed, and even more so if preparation of gelcoat not good enough.
Chances of osmosis in a boat of that age are low but the other thing to look at is if the gelcoat was damaged during stripping the old antifouling. If that happened then solvent from Gelshield could penetrate to the laminate and cause osmosis to start

Would that be the case if the over coating times were adequate to allow solvent to escape?
"Dry film of gelshield not enough" - you mean enough coats properly applied?

 

[dombuckley]

Gelshield 200 is the solvent based version so unlikely to have suffered from amine sweat.

Of course, you're quite right - I got mixed up with Gelshield Plus. "My bad", as I believe the kids say....

Good summary, by the way. Just goes to show that laying on a protective coating as a preventative measure (though that wasn't the case here) can actually create the very problem you're trying to prevent, if you don't follow the instructions.

 

[drakes drum]

Thanks very much for the replies. I am a novice at this so please bear with me.

The boat, a 2000 42 Bavaria had an extensive survey in July 2014 and their was no sign of osmosis. Their was a recommendation that the old anti fouling be removed and re applied. In August 2015 the boat was taken out to do this. The boatyard stated:

Bottom paint: in order to get off all the antifouling we will have to use a product, paint stripper.
After using this paint stripper the boat will have to sand the hull, paint with a primer, in this case Gelshield 200 (International) and then the antifouling. This was done in Lanzerote over a four week period in August.

The osmosis was present when hauled out this week.

Cheers, Ron

You will now get lots of posts from Bav owners saying that it cannot possibly be osmosis since German boats are immune. .

 

[Pasarell]

Would that be the case if the over coating times were adequate to allow solvent to escape?
"Dry film of gelshield not enough" - you mean enough coats properly applied?

Yes on both counts.
There is a fine-ish line between allowing sufficient curing time for solvents to escape and being able to overcoat without need to rub down again. Perfectly possible for anyone to achieve but needs good monitoring of time / temperature / humidity.

Dry film is the amount of cured epoxy remaining after all solvents have escaped. On metal substrates it's easy to measure but less so on GRP and this is why manufacturers specify the number of coats and wet film thickness (wft) to apply. A common problem with DIY application is incorrect wft even when correct number of coats applied leading to a low total dft and loss of effectiveness.

 

[Ron5]

It gets more interesting.

After the boat yard pulled out the boat on Friday, leaving it to dry and inspecting today I received an email this afternoon that says:

We do not think it is osmosis, We are doing some tests and see what treatment would be the best.

So the saga goes on. Not very happy to say the least.

Cheers, Ron

 

[Tranona]

Unlikely to be osmosis. Rare on Bavarias, or indeed any GRP boat from that era. The resins used, and the laminating processes have virtually eliminated osmosis. My money would be on blisters in the epoxy coating as already suggested.