# Polyurethane Glue & Biscuit Joints



## KnickKnack (Aug 20, 2008)

I recently acquired some D4 spec Polyurethane Glue - it was the only waterproof/resistant glue available.
Weird to use but I'm getting used to it.
My concern is its use in biscuit joints (probably dowel too, but I don't do those).
Last evening I was gluing a leg to a top, including a biscuit joint. 10 minutes in I decided it wasn't going well, so I pulled it apart. Using previous glue (white PVA, I guess), there's no way this would have been possible. My understanding is that the biscuit itself expands when it gets wet, which it does when using "normal" glue, but since the poly glue isn't "wet" in the water sense this doesn't happen.
Now I guess the glue will be gluing the biscuit in the joint, just not with the expansion side of it, but this worries me (one of my traits) since I thought that was where some/most of the strength came from.
I've surfed but can find nothing addressing this question.

Thanks in advance for thoughts, comments, (maybe even some reassurance?)


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## BigTim (Jan 17, 2008)

Most Polyurethane glues recomend wetting one surface to help activate the glue. Try wetting the biscuit, & glue up a test piece (or 2)with some scrap. After the glue has cured, usually overnight, try to destroy the joint. You could do the same test with pva glue & compare them.


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## Radish (Apr 11, 2007)

I'd worry about getting the biscuits before fitting them for fear that they would swell too much. Test board seems in order, and maybe Tightbond 3 makes more sense in this particular application. I used to use Gorilla glue for everything. Not so much now after FWW's glue tests. Now I use it pretty much for Incra joints or butt joints in pale woods only.


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## Blake (Oct 17, 2007)

Yea, the biscuits are supposed to swell once inside the joint. Why not just use Tightbond? That stuff is proven to work so well on tight side-grain joinery.


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## jcash3 (Dec 15, 2007)

Titebond III is waterproof, has a decent open time and is alot stronger than gorilla glue. Polyurethane glue has it's uses but is way over hiped. It's not as strong as PVA and can be a mess to use and clean up.


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## KnickKnack (Aug 20, 2008)

Thanks for the answers - I'll try the "add water first" method.
As for Titebond, well, I simply can't get it here!


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