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Old 18-02-2012, 15:21   #1
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Epoxy Barrier Coat

Could somebody explain to me the importamce of not sanding my epoxy barrier coat(fasrco low viscocity epoxy resin with west system 422 barrier coat additive)? And also why Ive been encouraged to paint the bottom paint so quickly after my last coat of barrier coat?
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Old 18-02-2012, 15:32   #2
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Re: Epoxy barrier coat.

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Originally Posted by clifflindsey View Post
Could somebody explain to me the importamce of not sanding my epoxy barrier coat(fasrco low viscocity epoxy resin with west system 422 barrier coat additive)? And also why Ive been encouraged to paint the bottom paint so quickly after my last coat of barrier coat?
Who told you that?! I don't know your epoxy nor your bottom paint but the only safe way is to first let the epoxy cure, then wet sand it 80-grit, then check if your anti-fouling is compatible with epoxy: if so, roll it on, if not, use a primer conform manufacturer instructions.

Hot-coating anti-fouling over not fully cured epoxy can go okay with some paints, but also really wrong with others. It can even prevent the epoxy from curing fully.

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Old 18-02-2012, 16:04   #3
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Im using hard epoxy bottom paint so I can understand hotcoating the barriercoat. But it would be better.for me (with respect to overlapping paint at the waterline) to not be in too much of a hurry to apply the epoxy antifouling.
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Old 18-02-2012, 16:13   #4
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Quote:
Originally Posted by clifflindsey
Im using hard epoxy bottom paint so I can understand hotcoating the barriercoat. But it would be better.for me (with respect to overlapping paint at the waterline) to not be in too much of a hurry to apply the epoxy antifouling.
I have done it myself too and also let it fully cure before painting. Results were the same, so it's safer to let cure first. There is no advantage to hotcoating, other than may be skipping a sanding. But that sanding also makes for a much better looking result.

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Old 18-02-2012, 16:24   #5
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Re: Epoxy barrier coat.

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Originally Posted by clifflindsey View Post
And also why Ive been encouraged to paint the bottom paint so quickly after my last coat of barrier coat?
Both Interlux and Pettit recommend applying bottom paint while the epoxy barrier coat is still tacky. Interprotect 2000 instructions say you should allow it to cure only until it is "thumb print tacky" before applying the bottom paint. If you let it cure fully, you take a risk that the bottom paint will fail to adhere and crack and peel off.
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Old 18-02-2012, 16:50   #6
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Quote:
Originally Posted by Ziggy
Both Interlux and Pettit recommend applying bottom paint while the epoxy barrier coat is still tacky. Interprotect 2000 instructions say you should allow it to cure only until it is "thumb print tacky" before applying the bottom paint. If you let it cure fully, you take a risk that the bottom paint will fail to adhere and crack and peel off.
Better read the specs like here: http://www.pettitpaint.com/fileshare...fiberglass.pdf

It all depends on which paint you use and also only with their own skip-sand primer. If you sand, you don't need to do this at all.

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Old 18-02-2012, 17:41   #7
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Re: Epoxy barrier coat.

Nick,
I believe the OP's question concerned application over epoxy barrier coat. See page 1 of Pettit's Gelcoat Blister Repair and Prevention.
It gives very specific windows for overcoating epoxy barrier coat with antifouling paint.
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Old 18-02-2012, 17:46   #8
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Re: Epoxy barrier coat.

i was advised to paint before epoxy barrier was dry also-- seems it makes a good coating and you can tell when to repaint as long as you dont use same color every time out of water. that paint remains on bottom as a part of the barrier coating unless you have a particularly vigorous cleaning.
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Old 18-02-2012, 17:52   #9
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Re: Epoxy barrier coat.

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Originally Posted by Ziggy View Post
Nick,
I believe the OP's question concerned application over epoxy barrier coat. See page 1 of Pettit's Gelcoat Blister Repair and Prevention.
It gives very specific windows for overcoating epoxy barrier coat with antifouling paint.
Ziggy,

I understand what you mean. But note that the document you link states it is for the Pettit epoxy primer system, not the epoxy system used by the OP. I agree with you that it sounds compatible but I wouldn't want to state that for sure. Also, the document you link clearly states that you can let cure and sand just like I recommend. The cure and sand always works.

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Old 18-02-2012, 18:03   #10
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Re: Epoxy barrier coat.

I did the bottom of my boat last spring. I did it because each time I took the boat out of the water in the fall the pressure washer would peel part of the thick layer of Micron CSG. It appearded that water got in between the antifouling and the Interprotect.
I scraped the antifouling and sanded the interprotect to remove the chocky surface. I did apply two new coats of interprotect and before it dried compleatly I applied the first coat (of a total of 3) in red Micron. The reason for the immediate application of the first coat of antifouling is to produce a chemical bond (and no sanding of interprotect 2000 needed), the next two coats you can apply at your leisure. In my case, the last two coats were black Micron, that way I'll know when the antifouling is ablated to its last coat (when red starts to show.) If you leave the interprotect to dry hard then you should sand it in order to promote adhesion. Hope this helps.

Jorge
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Old 18-02-2012, 18:07   #11
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Re: Epoxy barrier coat.

You're right--I'm not familiar with Fasrco, and Pettit does appear to say that sanding is acceptable. On the other hand, with Interprotect 2000, sanding is definitely not acceptable.

I think the problem with epoxy barrier coat is amine blush. There are some epoxies that don't blush, and sanding may be acceptable with them. If you do get amine blush, you will not get proper adhesion with antifouling paint unless you remove all traces of it (West System says thorough wash with water is sufficient, but sanding will not do it.)

Again, both Petttit and Interlux recommend applying antifouling while the barrier coat is still tacky. To be sure with Farsco, you should contact their technical help and ask.
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Old 18-02-2012, 18:29   #12
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Re: Epoxy barrier coat.

The correct bottom paint/primer will bond with the epoxy if done before it fully cures (usually just a bit of tack if I remember right) No problem with letting the epoxy cure and sanding, but the stuff fills sandpaper like it's going out of style AND if your bottom is not perfectly smooth (which it wont be if you rolled on thick epoxy) you will have thousands of little shiny spots that arent sanded if you look close. So I guess I understand most wanting to add the paint when they will chemically bond.... I have never sanded epoxy RESIN before primer for that reason..
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Old 18-02-2012, 18:32   #13
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Re: Epoxy barrier coat.

Quote:
Originally Posted by Ziggy View Post
You're right--I'm not familiar with Fasrco, and Pettit does appear to say that sanding is acceptable. On the other hand, with Interprotect 2000, sanding is definitely not acceptable.

I think the problem with epoxy barrier coat is amine blush. There are some epoxies that don't blush, and sanding may be acceptable with them. If you do get amine blush, you will not get proper adhesion with antifouling paint unless you remove all traces of it (West System says thorough wash with water is sufficient, but sanding will not do it.)

Again, both Petttit and Interlux recommend applying antifouling while the barrier coat is still tacky. To be sure with Farsco, you should contact their technical help and ask.
For Interprotect, there are some sidenotes too:

Quote:
When applying vinyl antifoulings such as VC Offshore and Baltoplate® to Interprotect, apply an extra coat and allow epoxy to cure overnight then sand with 80 grade (grit) paper to avoid wrinkling. When overcoating with VC 17m or VC 17m Extra allow Interprotect 2000E to dry for 24 - 36 hours, then sand with 180-220 grit sand paper.
On amine blush: I have tested this and found that the absolute best way of getting rid of it is by wet sanding. I follow that up with a quick pressure wash, no solvent wash. I have also tested dry sanding followed by pressure wash with equally good results. When I tried the wash with scotchbrite method, I got less good results but still no problem with next layer adhesion (which was epoxy too).

I am considering putting an Interprotect coat on next haul-out. Sounds like a lot of hard work again...

ciao!
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Old 18-02-2012, 18:34   #14
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Re: Epoxy barrier coat.

I guess I'm confused.... are we talking real epoxy resin or just the "epoxy" primer coat like interlux 2000?
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Old 18-02-2012, 18:43   #15
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Re: Epoxy barrier coat.

Here is the Pettit epoxy primer / barrier coat on the lead part of my keel. I followed all their instructions and it fell off next haul-out 3 years later.

I then decided to use my own method: sand to nice shiny lead and roll on West System resin + hardener. Directly put a steel brush to the wet epoxy with lots of effort behind it. This way you break the lead-oxide and put epoxy on without oxygen getting a chance. When that is cured, wet-sand and roll on another layer of epoxy. After that wet-sand again and anti-fouling.

Three years later was the next haul-out; it was rock solid. Shame I didn't take pictures
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