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post #11 of 17 Old 04-06-2017
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Re: glassing over removed thru hull. what glass to use?

Keeping in mind that a 2 inch hole in 1/2" glass needs ( to be done properly) a patch with a diameter of 14 inches. Its not a small repair! I've done 6 on my current boat this way and have 5 more to do. I use epoxy because its got better secondary bonding and allows me to build the whole 1/2" thick patch on the laminating table and apply it in one go ( sort of like applying wallpaper). I also back the patch on the inside with 3-4 additional layers of 1708. I use 1708 for all my patches because its easier to cut (without fraying) and makes a very strong repair. I put peel ply on top of the outermost layer and then smooth out the outer layer.

I've also had very good success covering my epoxy repair with gelcoat to blend into the rest of the hull. No issues with getting it to stick.
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post #12 of 17 Old 04-06-2017
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Re: glassing over removed thru hull. what glass to use?

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Originally Posted by pcmm View Post
Keeping in mind that a 2 inch hole in 1/2" glass needs ( to be done properly) a patch with a diameter of 14 inches. Its not a small repair! I've done 6 on my current boat this way and have 5 more to do. I use epoxy because its got better secondary bonding and allows me to build the whole 1/2" thick patch on the laminating table and apply it in one go ( sort of like applying wallpaper). I also back the patch on the inside with 3-4 additional layers of 1708. I use 1708 for all my patches because its easier to cut (without fraying) and makes a very strong repair. I put peel ply on top of the outermost layer and then smooth out the outer layer.

I've also had very good success covering my epoxy repair with gelcoat to blend into the rest of the hull. No issues with getting it to stick.
It is among the smallest, simplest repairs one could undertake. I taught my ten yr. old grand daughter in less than 10 minutes and let her go to it unsupervised. She did a great job that I did not have to redo.

Gelcoat (unless otherwise identified as vinylester) is simply an Iso or Ortho polyester resin with added pigment. It will NOT adhere (for long) to a cured epoxy without proper preparation and priming.The chemical compatibility is just not there.

The hysterical laughter you hear as you drive a way in your"new" boat ..... is the seller.
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post #13 of 17 Old 04-06-2017
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Re: glassing over removed thru hull. what glass to use?

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It is among the smallest, simplest repairs one could undertake. I taught my ten yr. old grand daughter in less than 10 minutes and let her go to it unsupervised. She did a great job that I did not have to redo.

Gelcoat (unless otherwise identified as vinylester) is simply an Iso or Ortho polyester resin with added pigment. It will NOT adhere (for long) to a cured epoxy without proper preparation and priming.The chemical compatibility is just not there.

Agreed it's not a difficult repair, but you do have to taper out an area that is 14 inches in diameter. Not just poke a few bits of cloth into the hole until its full.
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Re: glassing over removed thru hull. what glass to use?

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Agreed it's not a difficult repair, but you do have to taper out an area that is 14 inches in diameter. Not just poke a few bits of cloth into the hole until its full.
Given the standard taper of 13:1 you would divide the result by two as you would be tapering from inside and out. Therefore the 1/2' hull thickness becomes 1/4" for this purpose.

Although I do believe even that is overkill for such a small hole.

The hysterical laughter you hear as you drive a way in your"new" boat ..... is the seller.

Last edited by boatpoker; 04-06-2017 at 05:06 PM.
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Re: glassing over removed thru hull. what glass to use?

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Given the standard taper of 13:1 you would divide the result by two as you would be tapering from inside and out. Therefore the 1/2' hull thickness becomes 1/4" for this purpose.

Although I do believe even that is overkill for such a small hole.
I've found that its often not practical to do the taper on the inside. Its ideal, but often the truhull is in a location that makes the interior taper very difficult to accomplish ( often interior bulkheads are too close to to the tapers or the area too tight to swing a grinder properly so I've ended up having to do the repair from the outside.
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post #16 of 17 Old 04-10-2017
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Re: glassing over removed thru hull. what glass to use?

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Sand it, clean it, two part primer & gelcoat will adhere quite nicely but why would anyone put on gelcoat below the waterline ?

Agreed, but in case someone is doing glass work elsewhere on their boat and thinking gelcoat will stick...
As I said in previously, patch it and put Barrier coat on, bottom paint and go sailing. And yes, you *can* prep it so that it sticks but do you really think Weekend Warriors know this or will follow through?

CS 36M DIANTHUS
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post #17 of 17 Old 04-11-2017
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Re: glassing over removed thru hull. what glass to use?

Even for "weekend warriors" you can easily get gelcoat to stick to epoxy permanently. look up boatworks today on youtube.


He's pretty much proven that "gelcoat doesn't stick to epoxy" is complete BS. for underwater repairs I wouldn't bother but for topsides use gelcoat as the final coat.
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