Wood Biscuits And Urethane Glue

[Stephen Tashiro]

My understanding of wood biscuits is that they lock a joint tight when they swell after absorbing moisture. I think this means that you must apply moisture. Most directions on the web say to uses "carpenters" glue, which does contain water, so I understand why that works. But what about the urethane glues such as the honey colored Gorilla glue and the similar glue by Elmers? The directions on these foaming glues say to moisten the surfaces if they are dry, so it seems like it would be OK to dampen the biscuit before using these glues. Would that work?

[David DeCristoforo]

It will "work" but you must work fast after that because the biscuits will quickly swell to the point where you will not be able to get them into the slots! It's really not necessary if you are using the biscuits for alignment purposes only.

[Dell Moore]

I dunno, I get a similar feeling inside me when I think about this. Not as bad as the "Hey stupid, don't use the router that way, it'll chew you upi your thumb" (the voice I now listen to religously), but a similar "that's wrong" voice.

I think I would stick with the water based glues when it comes to working with bicuits. Gut says you won't get the same swell and expantion with a urethane glue.

Voice could be wrong.... Let us know...

Someday I'll tell you all an INSANE biscuit story, but it requires too much typing for now.

Dell

[Byron Trantham]

Why would you even consider another glue? The yellow glue works, period!:D

[Cliff Rohrabacher]

I have no respect for any of the urethane glues made.

They are all wimpy weak and useless in my not so humble opinion. They were invented for gluing teak in high humidity areas -where the teak is harvested. I am guessing it didn't work too well for the intended purpose but, Marketing people were not to be discouraged so they invented a million lies about the stuff and sold it to the public.

"World's Strongest Glue" was one of the lies. Strongest it most certainly is not. It's not even a runner up for tenth place.

I have used it successfully to create a bond between rubber balls and wood sticks to make beaters for Tongue Drums. Every thing else I tried to use it for would have been done better had I used something else like weldwood, Crazy glue, epoxy, or even plain old white glue.

On wood I say the stuff is the worst choice.

[Chris Padilla]

Stephen,

Tell us about your application for the biscuits and perhaps your reasons for wanting to use a poly glue.

[Alan Tolchinsky]

I wouldn't do it. First it will be a mess and second with no moisture the biscuit may not swell enough for a tight fit. Not a good idea IMHO.

[Doug Shepard]

I have no respect for any of the urethane glues made.

They are all wimpy weak and useless in my not so humble opinion. ....

Useless? Au contrair. When you're desperate to find something that will put a lovely purple/brown stain on your hands, there's just nothing better than poly glue.:D

[Stephen Tashiro]

My reasons for asking about urethane glue are these: I have it handy for simple carpentry projects and I like it. It isn't a strong glue but it also fills up the cracks in my unrefined joints as it foams so daylight that doesn't show through them. I use screws also. I usually don't use biscuits in simple carpentry. But now I want to make some "stretchers" to hold the canvases for paintings. The painting class teacher says that one way to make them is to join 4 boards at their corners in a miter and use a wood biscuit there. So I was wondering if I had to change my gluing habits. My impression of canvas stretchers is that they aren't a very sturdy construction. I think some are held together at the corners only by staples.

[Cliff Rohrabacher]

Useless? Au contrair. When you're desperate to find something that will put a lovely purple/brown stain on your hands, there's just nothing better than poly glue.:D

HA ha ha ha ha HOW VERY TRUE~!!

[Cliff Rohrabacher]

teacher says that one way to make them is to join 4 boards at their corners in a miter and use a wood biscuit there.


Ignore the teacher. At least ignore the teacher in so far as joinery is concerned.

The easiest, strongest, and most functional joint for your application using the least amount of tooling and skill are half lap joints.

The glue surface is tremendous and the skill level needed is only slightly above that of an average four year old. Half Laps were my main stay for years and years.

Throw away the gorilla glue. The gap filling properties are worthless. Yah they foam and block light but with zero strength. There is nothing for your application better than plain old white glue or titebond.


As an aside Mitre Joints with biscuits are not very strong and very hard to do well. The only glue surface you have is the biscuit interface the rest is end grain: that's never going to be strong.

[Paul Murphy]

I've used Titebond poly glue with biscuits. Poly in the slot, dip the bottom third of the biscuit in water, and quickly get the biscuit in the slot. No water on the other half, it will swell before the poly sets. Worked for me, and poly has a nice tight glue line that doesn't creep. I like the longer open time of poly for complex glue-ups. I don't use biscuits much for alignment of edge glued boards anymore, and it seems that poly is hard on planer knives, so I don't glue as many panels with it these days. I glued-up some of my beech workbench top with poly 15 years ago, and it is still in one piece. My dining room table is a poly glue up from 9 years ago, no problems so far...

I am using Titebond II extend a lot these days, but still like poly for assembling things like sliding dovetails as it doesn't swell and grab.

Hope this helps.

[Mike Henderson]

I have to disagree with Cliff. First, I've used titebond on miter joints and I get a good joint (for example, a jewelry box with mitered corners). Maybe not as good as dovetails, but I haven't had one come apart. Second, I've used miter joints (also on jewelry boxes) with a biscuit in them and they hold very well also. I used the smallest biscuits - I think it's 00 (not the little FF biscuits).

For what you want to do, the biscuit is easy to put in. But I'd use Titebond also, mainly because I don't like poly glue.

Mike

[george wilson]

Poly glue foam is about as strong as a styrofoam coffee cup. I won't use it. They used it for outdoor benches at Williamsburg's millwork shop,but that was all.

[Stephen Tashiro]

I found a website that agrees with the half-lap theory: http://www.sue-vesely.co.uk/sw_stretch_01.htm

She uses screws but no glue that I see.

Much of what is taught about oil painting concerns what the "old masters" did and whether it lasted for hundreds of years. But I haven't seen a discussion of what they did for the canvas stretchers. And I don't know if the old masters stretchers held up as well as their canvases.

I don't really trust the structure of a canvas stretcher not to warp eventually. Furniture can exist for hundreds of years without warping, but it has more parts holding other parts in place. My guess is that the best you can do is to pick very straight grained wood. and It seems to me best to seal them with something. The painting teacher is studying to be a museum conservator. which is why the issue of making things that last hundreds of years comes up. It is merely a playful discussion, but it's interesting to think about how one could do it.

[Tim Put]

I'm not actively recommending this but...

http://www.gutenberg.org/files/21531/21531-h/21531-h.htm#Page_184

[Bill White]

After several tries, I now have NO use for poly glue in any of my projects. PVA for my stuff.
Bill

[David Keller NC]

"The painting teacher is studying to be a museum conservator. which is why the issue of making things that last hundreds of years comes up. It is merely a playful discussion, but it's interesting to think about how one could do it."

If that's the case, then using poly or PVA is the wrong choice, at least if you want to know that it's going to last a couple of hundred years. Hot hide glue is the only truly long-term proven adhesive. That doesn't mean that PVA won't be around a hundred years from now - just that there's no way to tell without extrapolating accelerated aging tests.

Polyurethane, on the other hand, definitely will not last several hundred years. It oxidizes fairly quickly, and will likely break down after 2 to 3 decades.

But there's another reason not to use polyurethane glue for something that needs to be "archival" - it exudes an acid vapor that is a no-no around textiles and papers.