Adding glue before assembling a pocket hole joint is an extra step. It takes extra time and extra money.
But is it worth it? Should you add glue to pocket hole joints?
Adding glue to pocket hole joints does not make the joint stronger. However, it does help prevent seasonal wood movement. Therefore, wood glue helps preserve the longevity of the project, and should be added to pocket hole joints.
The fact that glue doesn’t make pocket hole joints stronger is counterintuitive to me, and I actually did a whole experiment to figure that out.
Plus, there are still some times to skip the wood glue, so keep reading!
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The Experiment: Does Glue Make Pocket Hole Joints Stronger?
So back in the day, I did an experiment testing the strength of a bunch of different joints to show if wood glue or screws were stronger.
This included both a butt joint with just glue, and a pocket hole joint.
The experiment itself was pretty low-key. I put the wood on a scale, then applied pressure with a clamp. The pocket hole joint (without glue) failed at 108 pounds.
At that point the screws started pulling out of the wood, and the joint wouldn’t hold anymore weight.
Today, I repeated this experiment with a pocket hole joint with glue. Everything else was the same – the scale, the clamp, the size and type of wood used.
I did get a table upgrade, though, if that’s worth mentioning.
I applied pressure to the joint using the clamp just as I had before.
The pocket hole joint with glue failed at 104 pounds, which was actually slightly less than the joint without glue.
I don’t think the difference point was large enough to really be significant, so I’m not going to say that I think glue makes the joint weaker.
But it certainly doesn’t make it any stronger.
I have a theory about that.
Why Wood Glue Doesn’t Make Pocket Hole Joints Stronger
When I got this result, I was mildly surprised. I always assumed glue would strengthen the joint, because that just makes sense. And then I thought about it a bit more.
In my long-ago experiment, I also tested glue-only butt joints. They failed at 60 pounds, far weaker than everything else I tried.
So in my experiment with the glued pocket hole joint, by the time the pocket hole joint was failing and the glue came into play, the weight applied had already far surpassed the glue joint’s strength, and therefore the joint immediately failed.
Why You Should Still Use Glue With Pocket Hole Joints
Wood glue isn’t going to make your joint any stronger, but it still serves a purpose.
One of the unfortunate facts of working with wood is that it grows and shrinks depending on the season. When humidity is higher (summer,) wood absorbs moisture from the air and grows. When humidity is low (winter) the wood releases the moisture and shrinks.
If you were wondering, this is why your doors always stick in the summer but not the winter.
It’s also why my coffee table sticks out a bit in the middle. I hadn’t learned this lesson yet when I built it:
More relevantly, this is also the reason you should still glue pocket hole joints if you’re making a project that you want to look nice.
In the winter, the wood will shrink, separating at the joint very slightly. This forms a gap that doesn’t very nice.
Wood glue helps prevent that. It holds the wood in place, and that gap doesn’t appear.
When You Shouldn’t Use Glue
If I’m making a nice project that has pocket hole joints, I use glue (and will continue to do so, even after learning it doesn’t actually add any strength.)
However, there are two main times I’ll skip the glue: 1) I’m making something I want to disassemble, or 2) I don’t care if it’s ugly.
Wood glue makes projects more difficult to take apart, for obvious reasons. If I intend to disassemble my project, I’ll skip the glue.
I’ll also skip the glue if I’m building something for my shop, like my cleat wall accessories. I don’t actually care if these separate a bit at the joint:
But if it’s a nice project that will go in the main part of my home, I still plan to use glue.