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Go Back   SailNet Community > On Board > Gear & Maintenance > epoxy barrier coat sun exposure how long is too long?
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Thread: epoxy barrier coat sun exposure how long is too long? Reply to Thread
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Topic Review (Newest First)
06-02-2012 04:39 PM
lancelot9898
Re: epoxy barrier coat sun exposure how long is too long?

I also have never heard of so many coats needing to be applied. When the boat was previously done there was just one coat applied via sprayer. Not sure of the thickness. Still think it's interesting that only a 10 year life is projected for that original coal tar epoxy barrier coat. Maybe more thickness was needed. As I get into doing this project more will be learned.
06-02-2012 04:06 PM
Stumble
Re: epoxy barrier coat sun exposure how long is too long?

Most manufacturers recommendations require a certain thickness regardless of the umber of coats. Interlux recommends 10mills, though how you get it is up to you. But it shouldn't take anywhere near 14 coats to get there, 4-5 is pretty typical.

I guess if you were doing an ultra high level racing boat, and applied very, very thin sprayed on coats it might take that many... But I have never heard of anyone doing that.
06-02-2012 03:51 PM
fiberglass1
Re: epoxy barrier coat sun exposure how long is too long?

"14 layers of epoxy barrier coat?" Sounds like either BS (of the let me impress you variety) or someone needs to do a little more research. The companies that make barrier coats spend a fair amount of time testing their products and they probably have a pretty good idea of how many coats are necessary. I've never seen 14 coats recommended by anybody.
06-02-2012 01:54 PM
lancelot9898
Re: epoxy barrier coat sun exposure how long is too long?

Oh...One other detail is that one yard that I spoke with puts up to 14 layers of epoxy barrier coats on the hull bottom after a peel.
06-02-2012 01:49 PM
lancelot9898
Re: epoxy barrier coat sun exposure how long is too long?

Interesting about your barrier coat. When my boat was new I had the yard put a coal tar epoxy barrier coat on the hull prior to launch. That was 25 years ago with the boat spending almost it's entire life in the water with a haul out every several years for new bottom paint. I wish I could tell you that I have no blisters, but that is not true. Now I find out that the barrier coat is good for only about 10 years so my question is why apply it in the first place if it needs to be removed in 10 years. (I don't think you would just apply another barrier coat over the old coat.) Seems like removing a barrier coat would be harder than removing just the gel, but I expect to find out soon. Trying to get a good price on a peel and then letting it dry our for a year. Good Luck
06-01-2012 10:41 PM
GaryHLucas
Re: epoxy barrier coat sun exposure how long is too long?

I'm pretty sure those are just air bubbles left when the glass mat was laid up against the gelcoat. It is nearly impossible to get all the air out during layup. Note that non-woven glass mat is ussually the first layer against the gel coat so that the woven cloth pattern doesn't print through the gelcoat. When moisture gets into the glass mat it follows the glass fibers and the fiber changes color in a very obvious way.

Gary H. Lucas
05-31-2012 10:12 PM
Stumble
Re: epoxy barrier coat sun exposure how long is too long?

Without seeing it they could be anything from a bad fairing job, to slight water intrusion points, old repairs poorly done, ect...

The really question is if they are wet after cleanup then you may have some moisture in the hull. Since you are planning to keep the boat out of the water for a while anyway I wouldn't worry about it. In the spring come back and fair the hull with thickened epoxy, then reapply a barrier coat, then bottom paint and off you go.
05-31-2012 09:05 PM
johnnyandjebus
Re: epoxy barrier coat sun exposure how long is too long?

Hello All

An update

I have started to sand into the hull, using a small belt sander. The ridgid mentioned in this thread. So far so good, it is small enough that I have enough control to not make a mess of things and it's dust collection is working well. At this point it is more exploratory work than a full hull strip. None of the areas are blisters, just areas that look like the epoxy has been compromised. For the most part things look dry but I am finding some pitting into the hull;



Can anyone tell me is this the result of a flawed layup at build time or a result of osmosis/hydrolysis?

After sanding I flush with water, let dry then wipe with acetone, a day later the pits are dry.

John
05-29-2012 08:10 AM
Minnewaska
Re: epoxy barrier coat sun exposure how long is too long?

A tarp skirt around the bottom of a boat can be a problem for an extended period. You should not attach them to the stands and, depending on whether you can stake them in the ground, they may not withstand a good storm.

I would not worry about a blister drying out properly if left exposed for a year.

My plan A would be to grind whatever you need to fix and have her soda blasted next year. They will tent her in to do that job and can probably do so earlier than you could stand getting under there for a couple of weeks. They only need a couple of days.

If this is all you have to do, I would actually sail her this season and do this all next year, including professional stripping.
05-29-2012 01:58 AM
Stumble
Re: epoxy barrier coat sun exposure how long is too long?

The one job I refused to do when I worked in a boat yard was stripping bottoms. Couldn't pay me enough to make it worth the pain of holding a sander up above my head all day.

There are a few, very few highly skilled guys that can strip a boat with a hand planer. Unless you have a few bottoms to ruin while learning how don't try it, but it is the best way to strip a boat.


These days though I doubt there is a yard anywhere that is using sandpaper to remove the bulk of old bottom paint. It is massively labor intensive, an environmental nightmare, and well known to cause health problems to anyone who breathes in the dust (remember bottom paint was designed to kill living things). At least around here most yards wont even allow you to sand your own bottom, let alone do it themselves.

If you have to strip the boat yourself chemical strippers are the way to go. They are much easier to clean up since the residue can be scraped into a bucket, and take a fraction of the work. Soda blasting is easier, and cleaner, but the machines are rarely rented.

Figure about $40/foot for chemical or soda blasting. For sanding, well again I wouldn't consider it so I have no idea. But it should be pretty cheap since all you are buying is sand paper.

If you happen
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