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Old 10-11-2014, 13:03   #1
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Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

So I have my boat on the hard and it will be staying put for 6 or 7 months until early May rolls round. I started sanding and found that there are just 2 coats of antifoul on the boat and no barrier coat. There are probably a dozen blisters. It looks to be easily manageable.

I figure while I have the boat out of the water all winter it might be a good time to go ahead and add a barrier coat since I don't want to spend months on the hard for a very very long time after I'm done here.

I'm at the point where I have to decide if i want to sand down to gelcoat or through the gelcoat and to the fiberglass. The sanding is going pretty easily and have sufficient tools to make quick work of it. I know that without the gelcoat the fiberglass will dry better before adding the epoxy barrier coat.

Should I go ahead and sand it all off, or is there any reason I might regret it? The gelcoat looks to be in great condition so I'm hesitant, but if its not serving any real purpose and might inhibit the drying process I guess I should get it off of there. Looking for feedback before I take the plunge...
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Old 10-11-2014, 19:18   #2
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

Quote:
Originally Posted by redpointist View Post
So I have my boat on the hard and it will be staying put for 6 or 7 months until early May rolls round. I started sanding and found that there are just 2 coats of antifoul on the boat and no barrier coat. There are probably a dozen blisters. It looks to be easily manageable.

I figure while I have the boat out of the water all winter it might be a good time to go ahead and add a barrier coat since I don't want to spend months on the hard for a very very long time after I'm done here.

I'm at the point where I have to decide if i want to sand down to gelcoat or through the gelcoat and to the fiberglass. The sanding is going pretty easily and have sufficient tools to make quick work of it. I know that without the gelcoat the fiberglass will dry better before adding the epoxy barrier coat.

Should I go ahead and sand it all off, or is there any reason I might regret it? The gelcoat looks to be in great condition so I'm hesitant, but if its not serving any real purpose and might inhibit the drying process I guess I should get it off of there. Looking for feedback before I take the plunge...



I wouldn't recommend sanding off the gel unless you have a solid reason, such as severe blistering or a high moisture meter reading. If you do, you will find the bare glass to be highly porous, leading to pinholing in your barrier coat which will require much extra work/extra coats. This is aside from the issue of fairness. Sand off every last bit of bottom paint, burning through the gel as little as possible, and you will get the best results. Long dry times acheive little this way, just open up the few blisters you have, dry them out, glass them back up, and coat it. It really is worthwhile to buy a moisture meter of your own, every boat owner should have one. I recommend the GRP-33. That way you know you are coating a dry boat.
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Old 10-11-2014, 19:28   #3
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

I would sand the bottom paint, gouge the blisters. Don't fill anything until a month or so before you intend to paint and relaunch... be sure to barrier coat now you've gone that far!
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Old 11-11-2014, 17:53   #4
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

Thanks for the replies! The gelcoat looks like its in good shape, so based on this feedback I'll leave it on afterall. Hopefully 6 months is long enough for it to dry out. I may end up investing in a moisture meter...
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Old 13-11-2014, 05:41   #5
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

Buy, pay or borrow a moisture meter now not later. Be too late later. Won't dry with gel coat on as the man says. Thanks Phil
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Old 13-11-2014, 06:17   #6
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

+1 on the meter!

If ya get it now, you'll hopefully have a very nice curve confirming your percentages...
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Old 13-11-2014, 08:24   #7
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

On the subject of barrier coats, Interlux has come out with a high solid version of Interprotect 2000. It's called Interprotect HS. Here is what they say about it.

InterProtect HS is a versatile high solids, two part epoxy, that can be used above and below the waterline as a primer for all substrates. As part of a gelcoat blister repair or prevention system, InterProtect HS uses the Micro-Plate Technology to substantially reduce water migration through the epoxy to the hull surface which could lead to blistering. Micro-Plates also provide protection from corrosion for metals. InterProtect HS is a high solids epoxy which means fewer coats to reach the desired film thickness. InterProtect HS also meets the most restrictive V.O.C. regulations and helps reduce solvent emissions into the environment.
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Old 13-11-2014, 14:04   #8
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

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Originally Posted by HopCar View Post
On the subject of barrier coats, Interlux has come out with a high solid version of Interprotect 2000. It's called Interprotect HS. Here is what they say about it.

InterProtect HS is a versatile high solids, two part epoxy, that can be used above and below the waterline as a primer for all substrates. As part of a gelcoat blister repair or prevention system, InterProtect HS uses the Micro-Plate Technology to substantially reduce water migration through the epoxy to the hull surface which could lead to blistering. Micro-Plates also provide protection from corrosion for metals. InterProtect HS is a high solids epoxy which means fewer coats to reach the desired film thickness. InterProtect HS also meets the most restrictive V.O.C. regulations and helps reduce solvent emissions into the environment.
2000 HS was designed, like most high solids, for the California market. It has lower VOC. I wouldn't recommend using it, most HS products do not apply or perform like their more toxic counterparts.
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Old 13-11-2014, 14:11   #9
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

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Thanks for the replies! The gelcoat looks like its in good shape, so based on this feedback I'll leave it on afterall. Hopefully 6 months is long enough for it to dry out. I may end up investing in a moisture meter...
as long as you break an glaze on the gel... it should dry out. at least that's been my experience on a couple of boats.
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Old 13-11-2014, 14:55   #10
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

"2000 HS was designed, like most high solids, for the California market. It has lower VOC. I wouldn't recommend using it, most HS products do not apply or perform like their more toxic counterparts. "

That's been my experience also. I haven't talked to anyone who has actually used the Interprotect HS but it wouldn't surprise me if it didn't want to flow out like it should.

That's certainly an issue for top coats but is it as important for a barrier coat? It's below the waterline, you want a thick coat, and you're going to sand it before you top coat it with bottom paint.
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Old 13-11-2014, 20:48   #11
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

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"2000 HS was designed, like most high solids, for the California market. It has lower VOC. I wouldn't recommend using it, most HS products do not apply or perform like their more toxic counterparts. "

That's been my experience also. I haven't talked to anyone who has actually used the Interprotect HS but it wouldn't surprise me if it didn't want to flow out like it should.

That's certainly an issue for top coats but is it as important for a barrier coat? It's below the waterline, you want a thick coat, and you're going to sand it before you top coat it with bottom paint.


Oh most definitely not, one of the best advantages to 2000 is that most bottom paints will chemical bond to it with no sanding. This saves much labor and provides a greatly superior bond. I would think 2000HS would apply similar to Tuff Stuff, which I dislike. You need to spray (through an airless) for a decent finish. It's a nightmare.
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Old 13-11-2014, 21:12   #12
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Re: Any reason I'd regret sanding off my gelcoat for epoxy barrier coat?

minaret, you're right, I didn't know you could avoid sanding 2000 before over coating with bottom paint. I had to look it up.

Here's what Interlux has to say about it:

Overcoating times will vary due to wide variations in temperature and humidity. The best method to determine when overcoating can
begin is to use the "Thumb Print Test". If you can leave a thumb print in the primer, and not get paint on your thumb, the primer is ready
for overcoating. Start testing the primer, 30 minutes after application, where you first started applying the primer. Continue testing every
15 minutes until the "Thumb Print Test" is passed, and then immediately begin applying antifouling paint. If the primer cures hard before it
is overcoated, an additional coat of Interprotect 2000E can be applied, or the primer can be allowed to cure, and sanded with 80 grade (grit)

They also say this about 2000 but not about HS.
"Sag resistance to insure the elimination of sags and runs during application"

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