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Old 06-03-2020, 12:06   #1
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Does my hull still need a barrier coat

After an osmosis treatment of peeling my hull and re-glassing with 2-3 layers of 1708 and epoxy resin, is there still a benefit or a need for the recommended 5 coats of barrier coat?
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Old 06-03-2020, 15:47   #2
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Re: Does my hull still need a barrier coat

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After an osmosis treatment of peeling my hull and re-glassing with 2-3 layers of 1708 and epoxy resin, is there still a benefit or a need for the recommended 5 coats of barrier coat?
https://www.westsystem.com/instructi...rrier-coating/
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Old 06-03-2020, 16:08   #3
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Re: Does my hull still need a barrier coat

Yes, the barrier coat is much better than an epoxy laminate. I recommend International Interprotect2000. It is very important to get the first coat of antifouling on right when the fingerprint test is positive (print visible but no paint on finger). If you wait too long, the paint falls off by itself.
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Old 07-03-2020, 10:29   #4
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Re: Does my hull still need a barrier coat

Thank you.

I figured it was still worth while, but it never hurts to ask.
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Old 08-03-2020, 06:29   #5
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Re: Does my hull still need a barrier coat

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Thank you.

I figured it was still worth while, but it never hurts to ask.
Now that you got the hull fixed and in great shape, is the best time for the barrier coat. In addition to epoxyís already good water proofing, it has mica flinters in there, that stack & overlap like roof tiles, good stuff
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Old 08-03-2020, 10:10   #6
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Re: Does my hull still need a barrier coat

Man my new boat has never had bottom paint only used in freshwater by pevious owner so do I need a barrier coat before adding bottom paint? I'll be sailing in Puget Sound
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Old 08-03-2020, 11:09   #7
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Re: Does my hull still need a barrier coat

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Man my new boat has never had bottom paint only used in freshwater by pevious owner so do I need a barrier coat before adding bottom paint? I'll be sailing in Puget Sound
You will have to sand the bottom so that the bottom paint will stick.
However, a chemical wash first to remove any wax is first, as you'll NOT want to sand wax into the gelcoat. Interlux 202, nasty smell, chemical gloves required, respirator, with protection for fumes.
After chemical wash, then sand.
Sand with 80 grit till it's not shiny, wipe it down using clean unused cloth rags,and 202, to remove any dust, tape, the water line, then bottom paint.
If its aluminum, you'll need a barrier coat, then bottom paint. After sanding the metal.
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Old 08-03-2020, 11:21   #8
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Re: Does my hull still need a barrier coat

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Man my new boat has never had bottom paint only used in freshwater by pevious owner so do I need a barrier coat before adding bottom paint? I'll be sailing in Puget Sound
You sure do because you now have gelcoat which is just polyester and not a good barrier at all.

You are in a great position as you donít have antifouling yet. What is very important is that you must de-wax the hull before sanding. You can buy special products for that. The wax is from the mold that the hull was laminated in.

After that, sand with 80-grit and do the 5 coats which is very easy. While doing the first coat, mark the time when you start and every 5 minutes go back to where you started and do the fingerprint test. When there is no paint on your finger but your fingerprint is in the paint, mark the timespan from when you started the coat. If you can do a full coat within that timespan, you are good... if not, you need extra people because when the fingerprint triggers, the first coat of antifouling must go on, even when the last barrier coat isnít finished yet.

I have one tip that I got when I did this and itís great. Masking the waterline: start with wide 3M original blue tape and mask precisely. This will be where the antifouling is painted against. Now take narrow tape and tape again but just a bit lower (1/8Ē, 3mm). Repeat that 4 more times. Remove one layer after every barrier coat and leave the wide one until 2 or 3 coats of antifouling are on. This way you stack the coats so you donít get one big step
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Old 08-03-2020, 11:26   #9
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Re: Does my hull still need a barrier coat

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You will have to sand the bottom so that the bottom paint will stick.
However, a chemical wash first to remove any wax is first, as you'll NOT want to sand wax into the gelcoat. Interlux 202, nasty smell, chemical gloves required, respirator, with protection for fumes.
After chemical wash, then sand.
Sand with 80 grit till it's not shiny, wipe it down using clean unused cloth rags,and 202, to remove any dust, tape, the water line, then bottom paint.
If its aluminum, you'll need a barrier coat, then bottom paint. After sanding the metal.
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Man I'm glad my boats on a trailer. 32 feet will take a day just to strip it maybe two to sand it then another day to paint it poof there goes another week
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Old 08-03-2020, 11:26   #10
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Re: Does my hull still need a barrier coat

Hahaha we got the same story

Hereís another product... it says no need to sand but you do
https://www.jamestowndistributors.co...t.do?pid=97453
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Old 08-03-2020, 12:05   #11
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Re: Does my hull still need a barrier coat

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Man I'm glad my boats on a trailer. 32 feet will take a day just to strip it maybe two to sand it then another day to paint it poof there goes another week
You really don't need to add more layers of barrier coat, as long as you don't sand thru the gelcoat, and expose The Glass (aka. FRP)
To be on the safe side, barrier coats protect the edges of the FRP that are closer to the surface due to the gelcoat being thinner there.
The Barrier coat isn't needed unless you sand those edges roughly and expose the FRP.
Polyester resin is a barrier coat in itself, and gel coat is polished polyester resin to make it more impervious to moisture incursion.
Add barrier coat if you want, but you'll have no problems with water into the FRP if you don't, it's just added protection, and cost.
Some, will disagree.
That's why it's a forum.
Cheers,
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Old 08-03-2020, 12:51   #12
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Re: Does my hull still need a barrier coat

FWIW, my 1975 Tartan 41, polyester boat, has never had barrier. It's just bottom paint over the gelcoat. No blisters in 45 years. I've heard about barrier coats causing blisters because they have sealed in moisture. So, before you apply barrier you need to ensure the underlayment is dried out... Personally, I'm on the 'don't barrier over gelcoat' camp, but if your boat is new, I'd ask the builder what they recommend.
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Old 08-03-2020, 12:52   #13
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Re: Does my hull still need a barrier coat

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Originally Posted by Boatyarddog View Post
You really don't need to add more layers of barrier coat, as long as you don't sand thru the gelcoat, and expose The Glass (aka. FRP)
To be on the safe side, barrier coats protect the edges of the FRP that are closer to the surface due to the gelcoat being thinner there.
The Barrier coat isn't needed unless you sand those edges roughly and expose the FRP.
Polyester resin is a barrier coat in itself, and gel coat is polished polyester resin to make it more impervious to moisture incursion.
Add barrier coat if you want, but you'll have no problems with water into the FRP if you don't, it's just added protection, and cost.
Some, will disagree.
That's why it's a forum.
Cheers,
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Thanks been here long enough to see the vast array of expertise. But its always a great starter as you figure out how it applies to you!
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Old 08-03-2020, 13:56   #14
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Re: Does my hull still need a barrier coat

Yes

You need a barrier coat

I’m not familiar with many common marine store paints

I’m typically using industrial products

A waterproof primer barrier coat system is composed of two primer paints

The first is a substrate primer engineered to promote maximium adhesion to substrate

The second primer promotes maximum adhesion with the antifoul

These two epoxy primers are applied “wet on wet “.

The antifoul is applied “ wet on wet “

There is no sanding between coats ... a strict overcoating time window, with no surface contamination , must be observed
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Old 08-03-2020, 14:12   #15
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Re: Does my hull still need a barrier coat

Any boat built after the 1974 oil crisis that does not have vynlester gelcoat below the waterline would benefit from a barrier coat. During the oil crisis polyester resin was reformulated which increased it's vulnerability to osmotic blistering.

My boat was built in 1985 and had hundreds of small blisters, most under a quarter inch and a few as big as an inch. They were not deep, just between the gelcoat and the laminate. When I bought it in 1990 it had just had a west epoxy blister job the year before. A lot has been learned about blister repair since then.

We cut out and ground out all the blisters in the fall and let the hull dry out over the winter (Chicago). In the spring we sanded off the bottom down to the West epoxy layer. Then filled and faired the blisters. Then five coats in Interprotect 2000. 17 years later a couple of dozen blisters appeared. We repeated the process and have not had a blister since (now 12 years).

I hope that now with ten layers of Interprotect 2000 it will never have to be done again.
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