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Old 10-12-2015, 10:03   #1
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Regular epoxy for barrier coat?

I have a small area that I have repaired near my dagger boards on a boat that stays in the water all year. The boat is cored with western red cedar and has two layers of glass on each side. The non-affected area has a few coats of interprotect2000 and then ablative bottom paint.

Can I simply overcoat my repaired area (Maybe 3 sq ft) with epoxy resin before painting and have an effective barrier coating? Perhaps add a bit of cabosil to thicken it up?
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Old 10-12-2015, 10:40   #2
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Re: Regular epoxy for barrier coat?

Hello, the best practice would be sealing with regular epoxy and after that apply an epoxy primer like Interprotect 2000 or any high solids epoxy. Do not use cabosil on the sealer coat, just plain resin, primer and antifouling.
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Old 10-12-2015, 11:18   #3
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Re: Regular epoxy for barrier coat?

The top coat should be unthickened epoxy, if you need to do some fairing work under this coat then micro balloons first, sand second, finish with a top coat of neat epoxy.

I assume you know this, but you cannot use just epoxy resin, it has to be mixed with the hardener to catalyze.
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Old 10-12-2015, 11:43   #4
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Re: Regular epoxy for barrier coat?

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Originally Posted by Stumble View Post
The top coat should be unthickened epoxy, if you need to do some fairing work under this coat then micro balloons first, sand second, finish with a top coat of neat epoxy.

I assume you know this, but you cannot use just epoxy resin, it has to be mixed with the hardener to catalyze.
Oh Man. I must have come across as a real maroon....

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Old 10-12-2015, 12:17   #5
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Re: Regular epoxy for barrier coat?

I remember reading something somewhere about epoxy not necessarily being impervious to water (much like polyester) and that purpose-made epoxy "barrier coats" employ little platelet structures to improve watertightness.

But I also just read west system's advice that their resin is fine for the task, just don't thin it, don't use fillers, and apply at least 2 coats, 3 or more if you'll be sanding + fairing.

Who knows.
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Old 10-12-2015, 23:00   #6
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Re: Regular epoxy for barrier coat?

Pretty sure vinyl ester is tops for being non-permeable to water, better than both both epoxy and polyester, and lies between the two for strength, cross bonding and cost...
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Old 10-12-2015, 23:25   #7
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Re: Regular epoxy for barrier coat?

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Pretty sure vinyl ester is tops for being non-permeable to water, better than both both epoxy and polyester, and lies between the two for strength, cross bonding and cost...
Nope, epoxy is the best across the board. It's major downside is that it is substantially more expensive.

This is always assuming you stay away from penetrating epoxy, which is about as water proof as a sieve.
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Old 11-12-2015, 01:20   #8
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Re: Regular epoxy for barrier coat?

The best advice is three or more coats of Interprotect. If you use straight epoxy you can add West 422 (which is powdered aluminum) to increase effectiveness.
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Old 11-12-2015, 03:25   #9
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Re: Regular epoxy for barrier coat?

Greetings and welcome aboard the CF, guillermosarrey.
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Old 11-12-2015, 14:51   #10
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Re: Regular epoxy for barrier coat?

Epoxy is better than vinylester for sure. Vinylester is better than Isothalic or
orthothalic polyester resins.
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Old 11-12-2015, 15:05   #11
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Re: Regular epoxy for barrier coat?

Quote:
Originally Posted by Stumble View Post
Nope, epoxy is the best across the board. It's major downside is that it is substantially more expensive.

This is always assuming you stay away from penetrating epoxy, which is about as water proof as a sieve.
What he said plus 1000!

If you are not sure about the epoxy you wish to use, check that it has 100% soilds. Any less than 100% means there will be "holes" in it after curing.
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Old 11-12-2015, 20:49   #12
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Re: Regular epoxy for barrier coat?

West has a "Barrier Coat" additive for their epoxy
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Old 11-12-2015, 23:22   #13
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Re: Regular epoxy for barrier coat?

Hmmm...


Seems to depend on whom one wants to believe. I've never used vinyl ester resins.


If you read the literature from the epoxy people most seem to say that their resin is definitely superior (as far as imperviousness to water) to polyester and leave vinylester kinda to the side.


If you read the literature from the vinylester people, they say that their resin is better than epoxy in resistance to permeability to water.


I've used isophthalic and orthophthalic polyester resins from cheap hardware store brands to high end surfboard quality and there is a wide variety in water absorption characteristics among them.


I've also used West, System Three, Mas, Resin Research and a variety of off brand epoxies, and I can assure you West and System Three are definitely not impermeable to water. I've only used Mas on dance floors and table tops, so can't tell you about it, and the story is still out on Resin Research because I've not yet done any work on previously coated surfaces to find out. Off brand epoxies don't get used in critical applications.

Within any 'class' of resins there are different formulations, any of which will affect the properties of the specific resin.

From the OPs' perspective, coating dry wood or repairs with either high quality epoxy or vinylester resin, followed by a specific purpose two part epoxy barrier coat is the probably the best (simplest and most economical) route. I'd certainly not trust either epoxy or vinylester alone without a specific barrier coat before bottom paint...
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Old 11-12-2015, 23:33   #14
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Re: Regular epoxy for barrier coat?

I believe I've read in the past that vinylester won't require a barrier coat which indicates it's resistance to osmosis problems. I've not heard that vinylester can be used for barrier coats though.

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Old 12-12-2015, 03:49   #15
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Re: Regular epoxy for barrier coat?

Greetings and welcome aboard the CF, CuChulainn.
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