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Old 13-03-2012, 13:43   #1
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Below the Bottom Paint

Was at the boat yesterday prepping for bottom paint. The dealer that did it last year used an ablative paint so that pretty much just rubbed off. But the last owner must have been using hard paint and it is flaking off in areas.

I need to strip it all off some time, but don't have time this year because i didn't plan for it.

On some of the flaking areas a dull looking white finish is showing. Would this be an applied barrier coat, a primer coat or could this be gel coat?

What suggestions for need to apply a primer etc prior to applying new bottom paint?
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Old 13-03-2012, 13:54   #2
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Re: below the bottom paint

The white coating is almost certainly the gelcoat. I'd apply 2000 before bottom painting, after a bottom paint removal of course. If the original bottom paint is flaking off down to the gel that usually indicates the boat was comissioned with a skip sander product. The rest will probably eventually flake off too. Take it back to the gel and apply 2000 if you never want to worry about your bottom again. Any blisters?
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Old 13-03-2012, 14:01   #3
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Re: below the bottom paint

The primer can be pretty light grey after some time. Try sanding a little spot and see. Otherwise I guess you're seeing gel coat. Time to remove all and get a good bond!
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Old 13-03-2012, 14:04   #4
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Re: below the bottom paint

no blisters

what's this 2000?

My plan is to scrape the loose spots, sand those areas, seal/prime, then apply my bottom paint

All I really what to achieve is for the bottom to stay reasonably un-fouled during the season and not have a bigger problem develop during the year. Next year I think I'm going to strip it all down and start over. That gives me a year to figure out whether to use a stripper, sander, or a blaster.
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Old 13-03-2012, 14:37   #5
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Re: below the bottom paint

When we bought our boat the bottom looked OK during the quick haul survey. However, after purchase and standing a few days out of the water prior to repainting, the existing bottom paint began to drop off in small sections. The Interlux rep. indicated that it was most likely that the prior bottom paint had been applied over a barrier coat that was too dry -- apparently timing between barrier and the first layer of bottom paint is quite critical. I just mention this as it looks like you will need to strip the bottom completely (as we did) then apply 2 coats of barrier before painting with fresh ablative ant fouling paint. What should have been a small job became quite big and expensive. The story of my life!!! Unfortunately, I think that just slapping bottom paint on the existing situation is a waste of time and paint!!
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Old 13-03-2012, 14:39   #6
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Re: below the bottom paint

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Originally Posted by Don Lucas View Post
no blisters

That's good.


what's this 2000?

Interlux 2000e barrier coat.

My plan is to scrape the loose spots, sand those areas, seal/prime, then apply my bottom paint

No seal/prime necessary for this. Just slap on a couple of coats of bottom paint after you are done with prep.

All I really what to achieve is for the bottom to stay reasonably un-fouled during the season and not have a bigger problem develop during the year. Next year I think I'm going to strip it all down and start over. That gives me a year to figure out whether to use a stripper, sander, or a blaster.

After you strip it all down, then you apply the Interlux 2000. 5-6 coats. Then 2-3 coats of fresh bottom paint. It won't be cheap.
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Old 13-03-2012, 14:58   #7
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Re: below the bottom paint

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After you strip it all down, then you apply the Interlux 2000. 5-6 coats. Then 2-3 coats of fresh bottom paint. It won't be cheap.
I just dealt with the same situation where the bottom paint was flaking, with a serious buildup of many years of hard paint.

They chemically stripped the bottom. The underlying gelcoat was perfectly sound, and blister-free. In those circumstances a barrier coat is superfluous. Just put new bottom paint on.

So at this stage, if you are not dealing with blisters, you can scrape the loose stuff carefully and re-paint. Your plan is fine, and you will probably get a season, and no damage to the gelcoat will result.

The consequences of scraping just the looser stuff are that you'll lose some speed from the rough bottom, and you'll probably be dealing with more loose patches by the end of the season. That doesn't really matter unless you're racing.

When you do get around to the full bottom job, the key is to be nice to the gelcoat. If you go steaming in with a harsh sander you WILL be needing barrier coat. The right kind of chemical stripper is the kindest way to proceed. Then evaluate whether the gelcoat is blister free and in generally good condition. Then evaluate whether the protection of costly barrier coat is justified.
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Old 13-03-2012, 15:12   #8
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Re: below the bottom paint

If is is going to be a year until you strip it, just scrape it and bottom paint it...why waste money now....save it for the big job
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Old 13-03-2012, 15:22   #9
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Re: below the bottom paint

The white could possibly be a barrier coat, Petitt is white. This year I'm stripping my bottom to the glass. Will apply 2 coats System 3, then fill any spots w/ Marine tex and fair. Then 3 coats Petitt barrier coat, and finally the anti-fouling. This is a lot of work, hopefully it will last till I die, except for the anti-foul of course..Michael..
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Old 13-03-2012, 15:24   #10
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Re: below the bottom paint

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The underlying gelcoat was perfectly sound, and blister-free. In those circumstances a barrier coat is superfluous. Just put new bottom paint on.


Who told you that? Just not true. We have contracts with several manufacterers to barrier coat brand new boats as we commission them-why? Because gelcoat is porous and therefore subject to osmosis which causes saturation, delamination, and blistering. All fiberglass boats should have a barrier coat on the bottom, unless they were built in epoxy. Even then I barrier coat because I've seen too many blisters in epoxy fairing compound. It's simple, if you dont want blisters barrier coat your bottom. In fact if you chemical strip a bottom to the gel and barrier coat it without sanding for tooth, it will fail. The rougher the grit you put on the gel the better the barrier coat will stick.
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Old 13-03-2012, 15:38   #11
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Re: below the bottom paint

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Who told you that? Just not true. We have contracts with several manufacterers to barrier coat brand new boats as we commission them-why? Because gelcoat is porous and therefore subject to osmosis which causes saturation, delamination, and blistering. All fiberglass boats should have a barrier coat on the bottom, unless they were built in epoxy. Even then I barrier coat because I've seen too many blisters in epoxy fairing compound. It's simple, if you dont want blisters barrier coat your bottom. In fact if you chemical strip a bottom to the gel and barrier coat it without sanding for tooth, it will fail. The rougher the grit you put on the gel the better the barrier coat will stick.
Absolutely, I totality agree..Michael..
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Old 13-03-2012, 15:41   #12
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Re: below the bottom paint

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Because gelcoat is porous and therefore subject to osmosis which causes saturation, delamination, and blistering.
Some manufacturers get blisters, and some hardly ever do. Correct me if I'm wrong, but 80s Bristols did not get a barrier coat. Yet 30 years later, they are blister-free. Are you saying after 30 blister-free years it's going to erupt into blisters in the next 3? No, because it was properly laid-up and cured. Sure, if your hull is hastily and badly constructed you want to do everything you can to keep water out. I hope you're putting the barrier coat on the inside of the bilge, too.
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Old 13-03-2012, 16:02   #13
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Re: below the bottom paint

Not that it has anything to do with my questions but; while I was at the yard yesterday I would wander around once in a while while resting up. There were a lot of boat and it was like a boat stand forest. A big mix of newer and older boats, some with some really rough looking bottoms that probably needed stripping years ago. But ............... I didn't see a single boat blister is the entire yard!

Maybe it is a Northeast thing with the water and 1.2 year season. or maybe this issue is pretty much over with (no to say some still don't get it).
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Old 13-03-2012, 16:03   #14
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Re: below the bottom paint

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It won't be cheap.
The only boat related statement that always applies!
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Old 13-03-2012, 16:04   #15
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Re: below the bottom paint

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Originally Posted by Don Lucas View Post
Not that it has anything to do with my questions but; while I was at the yard yesterday I would wander around once in a while while resting up. There were a lot of boat and it was like a boat stand forest. A big mix of newer and older boats, some with some really rough looking bottoms that probably needed stripping years ago. But ............... I didn't see a single boat blister is the entire yard!

Maybe it is a Northeast thing with the water and 1.2 year season. or maybe this issue is pretty much over with (no to say some still don't get it).

Do you live in a fresh water or brackish estuary? Common on the east coast. Salt is a primary ingredient in osmosis. Also with older boats that have a lot of bottom paint buildup you sometimes wont see the blisters until you sand off the paint. It's only big blisters that are really obvious.
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