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Old 23-02-2011, 06:20   #1
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Osmosis Prevention - Choosing the Right Barrier Coat

Can products like Interlux's 'Interprotect' or Epifanes's 'Epoxy Primer' be used as barrier coats to prevent osmosis, or is it best to coat with a two part epoxy like West System or MAS? Thanks in advance!
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Old 23-02-2011, 18:29   #2
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

FYI...Sherman Williams sells an very good 2 part barrier coat for a fraction of the cost of similar products. There are many bottom repair specialists that use this product..however they wont tell you it comes from the local paint store !
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Old 24-02-2011, 04:13   #3
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

We used inteprotect as our barrier coating to prevent osmosis. Follow the instructions carefully. Not the nicest job in the world to do, but not the worst either.
Fair Winds
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Old 24-02-2011, 04:54   #4
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

Both will work to a degree, although what I suggest as best...

Start with a new boat, or a hull that has dried for a few months. Sand hull bottom bare of ALL old paint... Then, a tape plastic skirt all around, and dehumidifiers help. It needs to test out as DRY with a moisture meeter.

Apply 4 coats of WEST with their grey "barrier coat additive", in 1 day. Wash off the blush, then sand the next day to a totally smooth glaze. Then repeat the above! Sounds like a lot, but this 8 coats will be more like 5 or 6 after sanding. This is a MINIMAL amount! A third application wouldn't hurt. (soft pad random orbit like a Porter Cable).

Next I would go on with 4 coats of "Bar Rust" in a contrasting color to the bottom paint.

This is followed by final sanding and bottom paint.

Now... keep a dry bilge! Switch to a dripless shaft seal, and / or build (or have built) sumps around the mast base , engine, etc. Line these sumps with epoxy like the hull bottom was. what ever it takes to keep a dry bilge!

This "prevention" is 10 times easier to do before getting blisters, than is the "cure for blisters" further down the road.

Hope this helps, Mark
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Old 24-02-2011, 05:16   #5
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

13 yrs on InterProtect, no blisters.
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Old 25-02-2011, 07:01   #6
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

Thank you all for the info! I will hope to line my bilge with a layer of glass laid up with epoxy, fill then fair and paint. Hauling out for the hurricane season has its advantages..! As for the outside, there is no doubt that prevention is the easier of the two tasks. A blister ridden boat is a depressing sight! Can West system be used over gelcoat successfully, or should the gelcoat be removed? What are the least toxic and most labour effective ways of removing bottom paint if you live in a place where sand blasting has not arrived??
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Old 25-02-2011, 07:57   #7
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

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Originally Posted by cgaskell View Post
Thank you all for the info! I will hope to line my bilge with a layer of glass laid up with epoxy, fill then fair and paint. Hauling out for the hurricane season has its advantages..! As for the outside, there is no doubt that prevention is the easier of the two tasks. A blister ridden boat is a depressing sight! Can West system be used over gelcoat successfully, or should the gelcoat be removed? What are the least toxic and most labour effective ways of removing bottom paint if you live in a place where sand blasting has not arrived??
I like the West System method too, although it is the most expensive method.

Make a tent/skirt all around the boat and start by sanding off all old paint and checking the gelcoat. Grind off gelcoat where it looks bad, is cracked, flaking etc. and just sand it where it looks good. When done, wash it with lots of water (and only water) and let it dry out for a week or so. When it's dry, apply a coat of epoxy without additives (just resin and hardener) and let it cure for 24 hours. If you have metal parts, like a lead keel, let somebody brush the wet epoxy into the metal with a steel brush (vigorously) while you continue coating the rest of the hull. After cure, wash it with water and a scotchbrite sponge to remove the amine blush (the waxy substance). As soon as it's dry you can start fairing the spots where you removed the gelcoat or that need fairing for any other reason. Use epoxy thickened with colloidal silica for this. When done and fairing has gelled (still sticky), apply another full coat of epoxy without any additives (resin and hardener). When this coat is gelled, start with the coats using the barrier coat additive (follow instructions in the West System brochure).

cheers,
Nick.
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Old 25-02-2011, 10:29   #8
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

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Originally Posted by Mark Johnson View Post

Now... keep a dry bilge! Switch to a dripless shaft seal, and / or build (or have built) sumps around the mast base , engine, etc. Line these sumps with epoxy like the hull bottom was. what ever it takes to keep a dry bilge!

This "prevention" is 10 times easier to do before getting blisters, than is the "cure for blisters" further down the road.
Rubbish

Plenty of wet bilged boats never develop blisters just as plenty of dry bilge boats still get blisters. Got any evidence for that theory?
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Old 25-02-2011, 12:55   #9
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

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Rubbish
Plenty of wet bilged boats never develop blisters just as plenty of dry bilge boats still get blisters. Got any evidence for that theory?
And plenty of smokers never develop cancer, just as plenty of non-smokers do develop cancer.
Not just rubbish - stupid.
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Old 25-02-2011, 14:14   #10
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

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And plenty of smokers never develop cancer, just as plenty of non-smokers do develop cancer.
Not just rubbish - stupid.
Sorry I didn't provide you with enough data Gord, just pointing out that it goes against what I've seen. Easy to find info pointing out that 80% of lung cancer victims are smokers. Not so easy to find info suggesting that a couple of inches of water in a bilge will lead to blisters.

http://www.dtic.mil/cgi-bin/GetTRDoc...f&AD=ADA206508
Hull Blisters: Know the Enemy
Blister & Laminate Hydrolysis in Fiberglass Boat Hulls
Here are a few articles about the causes of blisters, nothing in them or any other informed article I've seen that indicates a couple of inches of water in a bilge, which on many boats is a different piece of fiberglass entirely from the hull, will cause blisters.

So many important things to worry and fret over for boat owners, having to constantly keep your bilge bone dry because you think a couple of inches of water in there will cause blisters is not one of them.
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Old 25-02-2011, 22:22   #11
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Re: Osmosis Prevention - Choosing the Right Barrier Coat

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Easy to find info pointing out that 80% of lung cancer victims are smokers.
Which leaves the question how many of the group that doesn't get lung cancer is smoker, or what percentage of lung cancer victims live in cities or travelled with the underground etc etc. Statistics ...

Back to osmosis: how many blisters are caused by water in the bilge? My guess is 0.01% because somebody is gonna write he/she saw one.

cheers,
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Old 25-02-2011, 22:35   #12
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pirate Re: Osmosis Prevention - Choosing the Right Barrier Coat

Ok... time to stop talking crap... you got a blister inside.. you got internal osmosis... you got a blister outside you got osmosis...
You got something leaking outa your bilge through the hull like someone posted you got a major problem... I'vs heard a lot of crap about sealing epoxying your interior but... if you've the above... your in deep shit as far as I'm concerned...
Sorry all you 'Experts'... a simple seamans point of view...
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