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Old 21-07-2012, 17:25   #1
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Barrier coat

I am wondering how important barrier coats are for fiberglass boats. I understand that older boats are subject to osmosis blistering but what about newer boats (like for example a 2005 Catalina)?
Does barrier coating 'wear out' or loose it's effectiveness over time or is it a situation where once it's there it's good forever unless you get carried away removing old antifoul ?

Thanks !
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Old 21-07-2012, 17:37   #2
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Re: Barrier coat

My understanding (could be wrong!!) is that the barrier coat not only "seals" the FG but also helps adherence of the anti-fouling bottom paint. Be careful to observe manufacturer's timing schedule between coats of BC, and of BC to AF unless you want everything to fail!!
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Old 21-07-2012, 17:59   #3
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Re: Barrier coat

chrisjs is correct. All fiberglass boats get barrier coats except high end race boats that never stay in the water long enough to need anti fouling. Anti fouling bottom paint is not the same a barrier coat. Barrier coats do wear out more by time than anything else.
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Old 21-07-2012, 18:08   #4
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Re: Barrier coat

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Originally Posted by Jd1 View Post
I am wondering how important barrier coats are for fiberglass boats. I understand that older boats are subject to osmosis blistering but what about newer boats (like for example a 2005 Catalina)?
Does barrier coating 'wear out' or loose it's effectiveness over time or is it a situation where once it's there it's good forever unless you get carried away removing old antifoul ?

Thanks !
Also newer boats get osmosis. Sometimes more than the old ones. Probably related to manufacturing methods, quality control, materials used, etc..

b.
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Old 21-07-2012, 19:53   #5
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Re: Barrier coat

Provided the barrier coat is a minimum of ten mils thick and not abraded when removing bottom paint, it will continue to do it's job for a very long time.
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Old 22-07-2012, 05:32   #6
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Re: Barrier coat

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Provided the barrier coat is a minimum of ten mils thick and not abraded when removing bottom paint, it will continue to do it's job for a very long time.
10-4 on that. Phil Turner www.boatpeeling.com
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Old 22-07-2012, 05:43   #7
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Re: Barrier coat

regarding bottom paint on barrier coat,can the barrier be allowed to cure and sanded before bottom paint?
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Old 22-07-2012, 06:24   #8
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Re: Barrier coat

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regarding bottom paint on barrier coat,can the barrier be allowed to cure and sanded before bottom paint?
You must sand and profile the surface before bottom paint. I did a barrier coat on my boat two years ago and the manufacturer recommended that I coat the barrier coat with their bottom paint when the epoxy was still in the early curing stage. Later, the epoxy cured and the bottom paint started to peel off. In the area where it peeled, the surface was bright and shinny. I will have to sand all the bottom paint off the next time to get a good profile on the barrier coat so the bottom paint will stick.
Lesson learned.
PS I keep my boat in Stuart...PM me and we can talk about what you want to do.
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Old 22-07-2012, 08:10   #9
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Re: Barrier coat

I used BlueWater Marine Paint's Bottom Protect, and the directions on the cans talk about the "thumb print" test. After your last coat of epoxy barrier coat, wait an hour or 2 and push your thumb into the paint. If the paint comes off onto your thumb, then you need to wait, but if your thumb makes a thumb-print impression into the paint but no paint actually comes off onto your thumb, then it's time to start overpainting with anti-fouling. If your thumb makes no impression, then that means that you've waited too long, the epoxy is too cured, and you'll have to either put another coat of barrier coat on or sand the whole hull before putting your anti-fouling on.

I put 7 coats of epoxy on my boat.

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Old 22-07-2012, 09:06   #10
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Re: Barrier coat

any boat built after the change in procedure for building fiberglass boats is subject to the possibility of osmotic gelcoat blistering--seems spraying gelcoat makes gaps.... the old way was to hand paint 1/8-1/4 inch of the stuff into the mold before placing the roving and resin is the most protective kind of gelcoat possible.
the builders are not allowed to do that anymore-not since 1973, when the laws were changed -- must be sprayed now thank your legislators for imperfections, as they are who forced the industry to change from effective to ineffective gelcoat application.
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Old 22-07-2012, 12:11   #11
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Re: Barrier coat

Timing is CRITICAL when applying multiple layers of barrier coat and when applying the first layer of anti-fouling bottom paint. Ignore this at your peril!!!!!
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Old 22-07-2012, 12:22   #12
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Re: Barrier coat

To really know if you need a barrier coat requires you to know something about finerglass manufacturing. Starting from the outside in, a hull will have some number of woven glass layers applied to thehull. So long as these layers are fully wet out then extra resin rolled out they are pretty good at resisting water intrusion.

After the woven layers, in fiberglass there is then almost always a layer of either CSM (chopped strand mat), or mat. This layer is to prevent bleed through of the woven pattern and reduce fairing costs and problems. The CSM is applied by a gun that in one nosel is shooting out resin, and in the other is cutting fiberglass threads to pieces. These are then mixed as they are applied to the hull. This results in lots of little threads oriented every which way, including sticking out away from the hull. Mat is a little better but also has the random orientation.

Finally there will be a layer of gell coat covering everything.


Now that we have the layers in mind, let's work our way back to the inside following the water.

Gell coat is water permeable, it isn't even supposed to stop long term water intrusion. Right below this is that layer of CSM or mat... Remember that random thread orientation, they also act to help wick water into areas of poor wet out (extra resin). Basically the random thread orientation acts like a path for water to follow. Since it is very hard to ensure perfect wet out, there are always pockets that are problematic. The CSM is much worse for this since the threads also work directionally into the hull, not just longitudinally.

Then we have the woven layers. Rarely if ever do you see blisters here. It can happen, but these are the big, narley structual problem blisters that can delaminate and destroy a boat. Luckily they are very rare, since it is easier to wet out these areas. The only cases I have seen were caused by improper mixing of the resin in the first place.

What a barrier coat does is place a shield around the entire hull out of epoxy. Since epoxy is highly water impermeable, the entire hull becomes water tight on a microscopic level. Of course this requires a certain thickness to ensure complete coverage (typically about 7 mills, but check with your manufacturer).

There is also the question of what goo the builders are using to start with. For instance most carbon fiber boats are built with epoxy, and thus are naturally waterproof. So they don't need the barrier coat as much.

Vinylester resins are not quite as good as epoxy at resisting water absorption but are much cheaper. They are also stronger than polyesters. Still require a barrier coat, but not quite as desperately as...

Polyester resins are the cheapest out there. They are also the weakest, and absorb the most water. In fact the gel coat we talked about earlier that is water permeable is just a specialized polyester resin. In fact polyester is pretty terrible stuff, but it is cheap, so builders trying to hit a price point still use it. Otherwise it has nothing to recommend it. Epoxy barrier coats are required in all applications unless the boat is out of the water all the time.

note that this is targeted at modern boats. Some of the older hulls were nothing but CSM because they really didn't know the downsides to it. This did lead to some major problems with delaminating blisters, and made boats much heavier than necessary. In part because CSM is such a bad structual material.

Quote:
Originally Posted by zeehag View Post
any boat built after the change in procedure for building fiberglass boats is subject to the possibility of osmotic gelcoat blistering--seems spraying gelcoat makes gaps.... the old way was to hand paint 1/8-1/4 inch of the stuff into the mold before placing the roving and resin is the most protective kind of gelcoat possible.
the builders are not allowed to do that anymore-not since 1973, when the laws were changed -- must be sprayed now thank your legislators for imperfections, as they are who forced the industry to change from effective to ineffective gelcoat application.
This really isn't true. The application process of gel coat has nothing to do with blisters. Gel coat by its nature is water permeable, so, within reason, thicker gel coat won't really help.

Thick gell coat also has a lot of problems. It is very heavy, and very brittle. Most stress cracks in fiberglass laminates are directly caused by too thick an application of gell coat. I have never seen 1/4" thick gell coat and would be amazed at any builder who ever had this as a layup schedule.
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Old 22-07-2012, 12:25   #13
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Re: Barrier coat

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Originally Posted by brankin View Post
You must sand and profile the surface before bottom paint. I did a barrier coat on my boat two years ago and the manufacturer recommended that I coat the barrier coat with their bottom paint when the epoxy was still in the early curing stage. Later, the epoxy cured and the bottom paint started to peel off. In the area where it peeled, the surface was bright and shinny. I will have to sand all the bottom paint off the next time to get a good profile on the barrier coat so the bottom paint will stick.
Lesson learned.
PS I keep my boat in Stuart...PM me and we can talk about what you want to do.
I had a a bottom pro-done sucessfully without sanding. (Epoxy Resin barrier coat) However, I have seen some that didnt stick well also. Best to let it cure and sand I think.
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Old 22-07-2012, 12:58   #14
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Re: Barrier coat

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I had a a bottom pro-done sucessfully without sanding. (Epoxy Resin barrier coat) However, I have seen some that didnt stick well also. Best to let it cure and sand I think.
Most of the time bad adhesion is caused by an amine blush that appears while the resin is curing. It really depends on the resin, since some make a heavy blush, others are designed not to create any (these are as you might expect more expensive). Once this blush forms it has to be removed before anything will adhere, but if you apply the next coat while the first is still curing (called hot applying), you can get it on before the lush starts to form.

This is just an example of READ THE LABEL different manufacturers use different formulas, and have different application instructions.
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