Expert: Jamie Yocono - 11/6/2006

Question
I have been having some trouble with some night stands that I had recently built. The table tops are coming apart where they were glued together. Because I don't know much about gluing up boards I just jointed the edges to clean them up and then I just applied the glue, clamped them together, and let it dry. It all seemed to be fine until just lately when they started coming apart at the glue lines. Do you know any ways that I can prevent this from happening with the ones that I am building to replace these and with future projects?

Thank You
Michael Hickman

Answer
Hi Michael,

Welcome to the (sometimes frustrating!) world of woodworking!  There could be many reasons why your glue joints failed. I'll go though a few things that it could be, and hopefully you'll have successful joints in the future.

Off the top of my head, I'm thinking the problem is either with the glue, the wood or the way you clamped it together. Let's start with the glue.

If your glue is old, or has frozen, it's possible that it's spoiled. I used to live in a cold climate, and the glue I used was freeze/thaw stable, meaning it could be frozen and still work just fine. Try to ascertain if it's been frozen or not. Yes, glue can go bad, and it's more common than most would think. If it looks like cottage cheese, it's probably bad.

Also, you might want to check the bottle you have to see how old it is; there might be a "use by..." date on it, which might mean the glue was past it's shelf life.  

When I have a doubt, I'll glue two pieces of wood together, and then try to pop them apart with a chisel. In theory, today's adhesives are supposed to be stronger than the wood itself. So if you do that test, it SHOULD pop apart somewhere within one of the pieces of wood. That means that the wood will split apart before the glue line will fail. If it pops apart at the glue line, the glue is probably bad.

Next- let's talk about the wood. Some woods have a high oil content and don't glue together very well. You didn't mention the type of wood your nightstands are made of, but some of the woods that are oily include rosewood, teak and cocobolo. If you used one of these woods without cleaning the wood first (with mineral spirits), that's a likely cause for your joint failure. Also, wood that is green can cause problems. That means the moisture content is too high, and the glue probably never cured correctly. So the moisture content of the wood is another thing to check.

If you've ruled out the glue and the wood as the problems, then the answer might lie in the way you applied the glue. Glues have an open assembly time, meaning they can be spread and not set up in a certain amount of time. If you were spreading the glue and going too slowly, there's a chance the assembly time was too slow and the glue started to set up on it's own.

You know- this just dawned on me- are you sure you applied enough glue? There is something called starving the joint. That means starving the joint of enough glue to make an adequate bond. If you didn't apply enough glue, you can starve it. BUT- if you tighten the clamps too tightly, you can also squeeze all the glue out of the joint, thus starving it another way.

So you need to look at the amount of glue you used, how long the joint was open, and then- how tightly you cranked on your clamps. All of them can cause glue line failure.

You mentioned that you ran the boards over a jointer and cleaned up the edges before gluing them. If you machined them too slowly, you possibly burnished the edges, thus sealing them from being able to fully absorb the glue. Wood that's slightly rough glues up better than perfectly smooth wood. If you have a really good sawblade, you can even glue your boards straight from the saw, without cleaning up the edge. That's providing it's a straight edge, though.

Last thing- when you mentioned that the joints are just now splitting, it might have something to do with the fact that the nightstands are in a warm environment, and the wood is shrinking with seasonal movement. Still- in theory, the wood should split before the glue line, so it makes me think it's either your glue or your technique.

OK, good luck, I hope this helps. Please feel free to write back if you have any further questions after reading this. And if this answer was helpful... please take a minute and rate my service. Thanks!

Jamie Yocono
Wood It Is! Custom Cabinetry
Las Vegas, NV
www.wooditis.com