Hard epoxy bottom paint--a barrier? - SailNet Community

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Old 08-24-2007
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Hard epoxy bottom paint--a barrier?

Just wondering if you would consider 2 - 3 layers of hard epoxy bottom paint to provide any moisture/blister protection. I'm not referring to the real barrier coats like Interprotect, but just the hard bottom paints.

I am asking because the previous owner of our boat sanded the hull almost to the gelcoat and applied 3 coats of Trinidad SR bottom paint. When I haul the boat to add more bottom paint (has been in the water 2 years since the bottom paint was applied), I'll need to decide whether to sand those three layers off, or just add new bottom paint.

While I know I need to consider the condition of the paint, and at the very least ensure no flaking/loose paint, it would be helpful to know if leaving some of the existing paint on would provide some barrier coat/moisture protection.

I will likely paint with an ablative paint, to avoid adding too many layers over the coming years.

Thanks for any thoughts on this.

Frank.
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Old 08-24-2007
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Frank-

Most epoxies are going to be more water-resistant and less permeable than polyester or vinylester resins. So several layers of any hard epoxy-based paint, is likely to help reduce the risk of osmosis to some degree. However, it will not probably provide as much protection as a dedicated barrier coating will.
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Frank,
I'd say the easy answer is, if it ain't broke don't fix it. If you don't have blisters-something's working, right? And, I have learned that it makes little sense to remove paint that is still well adhered to a surface. Painting over it with a compatible paint makes sense; appearance not being a factor anyways.

Remember, the goal is to prevent blistering and it really matters little if your bottom is coated with partially hydrogenated soybean oil if it's working!
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Old 08-25-2007
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Frank,
I'd say the easy answer is, if it ain't broke don't fix it. If you have blisters-something's working, right? And, I have learned that it makes little sense to remove paint that is still well adhered to a surface. Painting over it with a compatible paint makes sense; appearance not being a factor anyways.

Remember, the goal is to prevent blistering and it really matters little if your bottom is coated with partially hydrogenated soybean oil if it's working!
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Old 08-25-2007
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Hard epoxy bottom paints are formulated to be pourous so that water can get to and activate the copper anti-fouling. Those microscopic passage hold moisture against the hull rather than creating a barrier. Unfortunately, That is the opposite of what you want for a barrier coat.
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Jeff, I wasn't aware of that as a possibility. If that's so, would you recommend sanding the hard epoxy bottom paint off, down to the gelcoat, before applying a few coats of an ablative antifouling paint? My guess is that the ablative paint will also be porous so that water will still be right up against the gelcoat--so would it make any difference?

My guess is that the only way to really protect the hull would be to sand it off, add a real barrier coat like Interprotect, and then bottom paint. However, in my situation where I leave the boat in the water year round (BC, Canada), I'm thinking I wouldn't get the hull dry enough in a reasonable time to avoid trapping moisture in there with the barrier coat, so I'm probably best off just applying bottom paint, watching for and fixing any blisters (so far none on the 1984 boat), and going sailing.

Thanks,
Frank.

Last edited by FrankLanger; 08-25-2007 at 10:49 AM.
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Frank,
If your going to remove the paint, why not epoxy resin coat the bottom ? After you have applied 3 or 4 coats, the bottom looks like a sheet of glass, but is as hard as a rock. I put vivid bottom paint over the epoxy resin coat on my boat.
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Quote:
Originally Posted by Jeff_H View Post
Hard epoxy bottom paints are formulated to be pourous so that water can get to and activate the copper anti-fouling. Those microscopic passage hold moisture against the hull rather than creating a barrier.
This is the answer to your question. Anti fouling paints ARE NOT barrier coats.
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