Sizing with PVA glues

[DC]

I've been on a few sites that recommend sizing the wood with PVA before gluing with PVA. I've also been on a few sites that say PVA won't glue to dried PVA. They say you have to take all the old glue off and make a fresh joint. What's your take on this?

[PatM]

My take is that you should use epoxy.

[PEARL DRUMS]

Pardon my ignorance. What is a PVA glue?

[High-Desert]

PVA glue is just wood glue. When sizing, you don't let the sizing layer dry, the point is it let it soak in for a few minutes, then apply a bit more, then place together whatever you are gluig. Applying glue, joining, and then clamping squeezes the glue out of the joint, the the wood will absorb the glue. Robbing your joint of enough glue.

[osage outlaw]

I size the back of a bow with TB and let it dry before gluing down a snake skin with TB.  I've never had an issue with it not sticking. 

[PatM]

Pardon my ignorance. What is a PVA glue?

  PolyVinylAcetate. Essentially white and yellow carpenter/woodworking glues.

[PEARL DRUMS]

Got it. When I use rawhide or snake skins, I size the back the night before with wood glue. Then add another of wood glue and the skins/rawhide the next day. I've never had a failure in either regard, maybe I'm just lucky so far.

[bow101]

PVA glue is just wood glue. When sizing, you don't let the sizing layer dry, the point is it let it soak in for a few minutes, then apply a bit more, then place together whatever you are gluig. Applying glue, joining, and then clamping squeezes the glue out of the joint, the the wood will absorb the glue. Robbing your joint of enough glue.

+2

[DC]

I can understand that sizing may help as long as you don't let the size coat cure right out, that makes sense. I was under the impression that you were to let it dry like PD does. That's the one that goes against what I've read about PVA not sticking to cured PVA. Maybe there is not a lot of stress on a snake skin. I can see the size coat "water proofing" the back of the bow a bit. That may help since snakeskin is a bit "waterproof" itself.

[PEARL DRUMS]

I have done it that way with all my rawhide backing as well. Like I said, maybe it is just dumb luck. I will continue doing it until it fails me.

[High-Desert]

When they say it won't stick, it's not like it will just fall off, and when you size the back, there is still wood available for the glue to bond too, it's jut not idea for joints under stress. The tensional stress on snake skin or rawhide backing is not all that high compared to some woodworking joints need to hold up. The backing is flexible as well. You may see a different result if you tried gluing on a hickory backing with the sizing glue dry, where the hickory is puttin quite a bit more stress on the glue joint than snake or rawhide.

Eric

[PEARL DRUMS]

I can buy that, Eric. I do it on skins and rawhide for one reason, keep the dampness from both out of the bow when I apply them. When I glue a hard backing on I don't size, of course I use epoxy so I don't need to.

[DC]

As far as personal experience goes, all I've got is trying to repair chairs when the glue joints crack and they start to wobble. I've pulled them apart and squirted PVA in the joint and clamped them up for a day or so. The new joint will crack after a short time and the chair starts to wobble again. I read that this is because PVA won't stick to cured PVA. Last time I fixed a chair I flooded the loose joint with CA. That was months ago and the chair is still solid. With this experience I questioned "sizing". Maybe a chair joint is just a really highly stressed joint.

[Pat B]

If the wood is super dry you could wipe it with a damp rag first before adding the glue to help the glue sink in to the wood better.
 I've never sized wood first before gluing with TB glues and never had a glue failure.

[Marc St Louis]

Pardon my ignorance. What is a PVA glue?

  PolyVinylAcetate. Essentially white and yellow carpenter/woodworking glues.

Not quite.  There's also aliphatic resin emulsion, that is the yellow glue