Best Glue For Box Joints

I received this question in episode 6 of the Ask Brian Boggs Show:

I’ll be making a Maloof dresser using box joints, I presume you mean finger joints, to join the carcass as you did with some of his. Do you think wood glue would make the joints too tight during glue-up? I’m presuming you mean the PVA wood glue. These are all wood glues we’re talking about. If so, would epoxy be my best bet?

Again, the wood glue or PVA glue is not a problem here. But you want each of those fingers, as they come together, to have a couple thousandths of an inch of space between them. That’s not a visible space and it’s not going to feel like a space. It’s gonna feel like a snug joint. But if you put a caliper on the fingers of those joints, and put a caliper on the spaces of those joints, if you’re really careful you should be able to discover that there’s a couple of … in a perfect fit, the fingers are just a few thousandths smaller than the space themselves.

That’s just the dynamic of assembly, and if you’ve got that and you apply glue to both parts, you shouldn’t have an excessively-tight fit. You should be able to put that together beautifully and get a really strong joint.

I don’t think epoxy is gonna solve the problem. In fact, if anything you want them slightly looser and you’ll need to allow the epoxy to soak into all the fingers before assembly, whereas the PVA glue will bond quickly enough on the surface and does not need to penetrate that much. And just a reminder in case you weren’t … on the last episode, the reason you need epoxy to penetrate is because it’s going to penetrate. The wood is going to soak it up, and if it soaks it up too much after you’ve assembled, then it can pull enough epoxy away from that joint that you won’t have enough epoxy material in there to create the chemistry needed to have that two-part bond action that epoxy’s really good at. So I don’t think your wood glue is an issue.

I would caution to not use too much, so that if you get the end-grain of these box joints saturated with a lot of moisture from the glue, that can cause them to swell up more than needed. But just a nice even coat on all the parts- be sure to coat the end-grain as well on those joints. The end-grain in the joint, not the end-grain that, extended, will be exposed at the end. Just assemble it carefully, and clamping pressure is real critical on that, so I would stick with what you call wood glue. And thanks for that question. That was a good one. That’s another joint I use a lot of, but I have had several designs where I used that, and I really like the way yellow glue performs in that.