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Re: Gelcoat, epoxy & glassing over a thru hull

 

RegJust use epoxy and glass. Probably thicken it with fumed silica, it makes it easier to build layers, you can fair the thickened epoxy somewhat. Then a final two coats of epoxy to seal everything. You can run a bit of epoxy over the lip onto the original bottom to seal everything.? Just sand it enough to give it tooth.
You need to see what is above the waterline and determine if it's been painted over gelcoat. If you're going to paint anyway I would just use epoxy mixed with fumed silica and microballoons for filler, then a final couple coats of epoxy. Obviously you would need to sand and prep first.
If you want to stay with gelcoat you probably should get someone to look at it first. It probably won't match but that's just a quick opinion. All of this is just one man's opinion obviously.?
Your boat will likely never have gelcoat reapplied to the bottom. There isnt an epoxy polyester incompatibility issue as long as its epoxy over polyester.? Epoxy sticks well. Really well. Just sand first. If you use a ready mix fairing compound,? make sure you can use it below the waterline. Really no need if hole is small, just use fumed silica to thicken and fair it well before it sets up. If you must use a fairing compound then topcoat it with epoxy.

Regards, Rob. (Early T27 I haven't seen yet because I'm still filling holes in my Allied.)


On Thu, Aug 15, 2019, 11:34 PM Jeremy Shaw jeremy@... [T27Owners] <T27Owners@...> wrote:
?

Hello,

I know just enough to be dangerous!

I removed an old depth sounder and have a nickel sized hole in the bottom of my boat below the waterline now. All I need to do now is glass over the hole. I am familiar with the basics of the 12-to-1 bevel, building up the layers, etc.? But.. the devil is in the details.

I have an early model T27, Hull #154, 1965.

My understanding is that these boats are polyester resin. It is generally safe to put epoxy on polyester, but not the other way around. And, apparently, gelcoat is a type of polyester resin.

So.. now I have questions. Did my boat originally have gelcoat under the bottom paint? The top-layer of bottom paint is an ablative paint - micron extra. But I don't really know what is underneath..

Maybe I don't care? Maybe I just use epoxy and glass over hole. And then use whatever primer and other treatment interlux says to use before applying micro extra to the patch?

My concern is that if someone later tried to reapply gelcoat to the bottom, there would be a place where it wouldn't work right? Or maybe my boat never had gelcoat below the waterline? Or perhaps it is absurd to think anyone is ever going to try to reapply gelcoat to the bottom? Also, I noticed that after the fiberglass is epoxied in place, people usually apply a layer of fairing compound over the epoxy to smooth things out. Perhaps the gelcoat would be able to adhere to the fairing compound masking the epoxy<->polyester incompatibility issue?

It seems, at the very least, that if I use epoxy for the patch, that I won't be using any gelcoat on top of the patch regardless of what is on the rest of the bottom. I guess that is not an issue?

What if I was patching above the waterline and wanted the best matching finish? Would I want to use polyester resin instead of epoxy so that I could have matching gelcoat applied? Does my boat even have gelcoat? My hull is a standard blue color,



As noted, I know enough to know there could be an issue, but not enough to know if there is an issue.

Thanks,
- jeremy
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