How to overcoat Copperbot?

[Lynette]

A friend is having problems overcoating the Copperbot antifouling that came with the boat they bought.

He decided to use Sea-Jet 033, which has done well in tests lately. He was told that there should be no difficulty overcoating Copperbot. But when the primer was put on, the Copperbot has blistered in places.

What's gone wrong? Could it be anything to do with the acetone thinner in the primer? Any help gratefully received.

 

[vyv_cox]

That's quite a surprise, I also would have thought that Coppercoat would resist attack, even from acetone. There's a post about two or three down from here that mentions an International barrier coating that might work. Also Gelshield (not Gelshield 200) is solvent free and could be expected to provide a barrier. A coat of West could perhaps offer the same. These are quite expensive ways to go, and it might even be cheaper to blast off the Coppercoat and start again.

 

[Lynette]

Thanks for your help. I went and took a look yesterday afternoon, and I rather suspect that the cause is osmosis. My friend had exposed most of the blisters - in some cases the gelcoat looked OK, but in most the gelcoat was also blistered or broken, and there were slight traces of moisture behind (no noticeable smell when I got there). I'm sure this wasn't visible when he started, so perhaps repainting has loosened the Copperbot just enough for problems underneath to reveal themselves.

This is a boat that is annually lifted for several months and of a make with a good reputation as far as osmosis is concerned. The blistering is most frequent near metal fittings (e.g. the lower pintle), and if it is osmosis, I just wonder whether the Copperbot could be implicated.

Its not widespread - my suggestion was simply to let the blisters dry out, fill with epoxy and continue; review again next year. What do you think?

 

[vyv_cox]

I hope you are right - that's exactly what I'm doing. None of my blisters was large but there are many of them. I've scraped off all the antifouling and am now sanding all over to get down to the Gelshield 200 that was applied 11 years ago. Very few blisters are burst. I'm going to fill any obvious open ones, then Gelshield 200 3-4 coats and leave it for a few years when I intend to have another look in Spain, where treatment is far cheaper.

I spoke to International about it at LIBS and they proposed exactly this treatment, although they only said one coat of Gelshield 200. Also, the advice on www.yachtsurvey.com seems to be the same - fill blisters unless they are enormous, gelshield and carry on as before.

 

[castaway]

Im quite interested in this subject as my 30yr old boat has mild osmosis. This has has some epoxy treatment in patches ( I have the recipts from 12 years back).

I have had the bottom slurry blasted to get a good look at the surface to assess the "finish", and although there is some mild oz still occuring there is no nasty smelling weepy blisters.

Interesting thing is that my surveyer has recomended that best move is to avoid fairing up the blistering with further "chemical" type epoxy treatments for 2 reasons (1). that the hull is still a bit too damp ie above 12 on the moisture scale and (2) that there is a very definate case for not putting 2 types of chemicals together ie polyester and epoxy.

So he says use a non reactive fairing compond (possibly Blakes underwater filler)
and then A/Fouling primer.

Of course he added the caveat that the only permenant fix was to have the boat peeled steam cleaned and epoxy coated... then added that this was by no means all that it is cracked up to be::::

I personally feel that we should all just get used to living with some oz on oldertype GRP boats and all important lift then for at least 4 months each year.

Have fun. Nick

 

[Lynette]

Thanks Castaway. For a 30 year old boat your advice is good, though my friend's is probably only about 12 years, has been lifted out religiously each year, so oz (if thats what it is) is a bit of a nasty shock. The Copperbot is epoxy based and one might have thought it would have provided protection.

I've not previously heard any objection to using epoxy to cover up blisters in GRP. Isn't that effectively what happens in a standard osmosis repair?

 

[vyv_cox]

I believe it is absolutely normal to overcoat polyester with epoxy. Many boats are built this way now, with bulkheads bonded into the hull using West fillets. International certainly sell a lot of Gelshield and Gelshield 200 for this purpose. The point about a dry hull is a good one though, if epoxy won't let water in it won't let it out.

 

[castaway]

Hi Lynette Re this epoxy issue. How I read it is that there are 2 factors that should be looked at very hard before putting an impermiable layer over any old hull bottom, and that is :a: Is the hull going to be dry enough and :b: Are any of the blisters weeping styrene, because if they are you will end up with chemical cocktail and a real mess.

Epoxy coating is fine either if its a new boat (that is thoroughly cured) or a hull that has been peeled and dried, anything else and you have a potential problem worse than the one you started with.

My last boat i built in the garden and I epoxied it "from new" when the hull was approx 5 years old and it went on super and has never caused a prob... But this and the peeled option are the only ones i would feel happy introducting the E word into........ Makes me wonder how dry the hull was when the Copperbot went on?

Regards Nick