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Building a chair out of glue

Posted: Wed Dec 12, 2018 4:12 am UTC
by Eebster the Great
It is a surprising but well-known fact that modern wood glue is much stronger than wood. When I first learned this as a little kid I was both fascinated and suspicious: how could the fastener be stronger than the main construction material? Why not just build everything out of glue?

That's obviously a foolish idea for many reasons, not the least of which is cost, but the question lingers. Could you, in principle, build an entire chair (or much larger structure) out of glue? After all, we could easily build everything out of cement, except that cement is not very strong without an aggregate with which to form concrete. But wood glue seems intrinsically strong, impressively so. With enough free glue, could we really just pour an entire piece of furniture into a mold and let it set? If there are surface issues, could we build a chair out of glue and then add plywood, cardboard, plastic, or other surfaces to finish it? What would the material properties of such a structure be?

Considering that the only component melts at ordinary temperatures, I assume these pieces would be ridiculously impractical, but I don't know enough to tell if my assumption is correct. What would such a chair be like? Would it be pleasant to sit in? Could it last? Could it really withstand the wear of ordinary use similarly well to, or even better than, a common wooden chair? Could it ever be affordable?

Just yet another of the random passing questions I leave in xkcd's capable hands.

Re: Building a chair out of glue

Posted: Wed Dec 12, 2018 4:45 am UTC
by Sizik
Looks like wood glue is polyvinyl acetate. I can't find any mention of it being used as a structural material, so I feel like it would just be a poor-quality plastic chair.

Re: Building a chair out of glue

Posted: Wed Dec 12, 2018 1:49 pm UTC
by Soupspoon
I suggest an experiment with an actuator-driven glue dispenser and an X/Y(/Z)-plotter with a suitable template and schedule to follow

I mean, that's 3d-printing. Not even like 3d-printing, but it is. Laminarity might mean it's not as good as 'cast' volumes, but I suspect that the tricks you'd need to get it to set throughout (in a mould it doesn't, in turn, irrevocably stick to) are going to be complex enough to dismiss that method.

(As to suitability, the strength of the glue probably derives in a large part from its flexibility, capable of bouncing back from stresses that would splinter wood. You'd therefore have to heavily account for that, rather than just use the volumetric footprint of a wooden chair but composed of the set glue polymer matrix. You might even end up having to copy a beanbag-chair, let someone sit on the membrane filled with the glue to create the ideal impression, encourage its curing by time/other methods (with or without the occupant still occupying it) and then end up with a highly specific and personalised seat. Middle-ground would be like this but at the scale of merely a 'cushion' with tapered leg 'framework' created beneath it (before, during or after the caboose-casting process) and any other features needed to make it as not merely a tooled stool, odd ottoman or rough pouffe. IMO.)

Re: Building a chair out of glue

Posted: Wed Dec 12, 2018 2:20 pm UTC
by p1t1o
glue chair = plastic chair (it might not be the exactly right polymer, but its pretty danged close enough)

Think about it - take a plastic chair: if made from wood of the same thickness, it would be extremely fragile, but a plastic chair is more than robust enough for some reasonably heavy-handed use.

Re: Building a chair out of glue

Posted: Wed Dec 12, 2018 3:01 pm UTC
by Tub
The premise is a bit simplified. Wood is likely to split along the grain, and its strength depends a lot on the orientation of the wood and the type of force you apply. If you apply forces that the wood is weak against, then it'll often break along the grain instead of along a glued seam. For different forces, results vary.

The strength of a glued seam is different from the strength of a ball of glue on its own.

The wood glue I remember was flexible, even after hardening. That's fine for a thin layer between two pieces of wood, but will have a noticeable effect on a larger structure.

Soupspoon wrote:I suggest an experiment with an actuator-driven glue dispenser and an X/Y(/Z)-plotter with a suitable template and schedule to follow

The low-cost variant of that experiment is a bottle of wood glue and a steady hand..

You can start with something really simple. Just draw a circle, let it dry, see if you can squish the circle. Or draw a line roughly the size of a toothpick, then compare strength and flexibility to the wooden one. You just need that bottle of wood glue.

Re: Building a chair out of glue

Posted: Wed Dec 12, 2018 3:59 pm UTC
by Zamfir
I have used the non-glue version of wood glue for some things. It is called EVA, ethyl vinyl acetate.

It's nice stuff for its applications, but not as a structural replacement for wood. It's pricy per kilo and its flexible (can stretch a few hundred percent). Neither of which are good for furniture, which is designed more for stiffness than pure strength. EVA is typically used as a foam. Then its tough, rubbery and smooth. Good for, say, the inside of ski boots, or acoustic decoupling.

Edit: Croc shoes are made from EVA. That's what you get, when you make wooden shoes out of wood glue

Re: Building a chair out of glue

Posted: Wed Dec 12, 2018 4:34 pm UTC
by Soupspoon
Tub wrote:The low-cost variant of that experiment is a bottle of wood glue and a steady hand..

I aint got the patience. I'd rather scratch-build a glue-deposition robot, that can be used repetitiously, consistently or adjustably to investigate optimum timings and quantities upon the end-product. Which would need a lot of glue, and possibly fume-hood ventilation. ;)