It’s a sticky situation – What Glue to Use?

In starting to add rings and different woods to my custom drums, I want to make sure they remain stable for years to come.? A new project I’m working on has me thinking about joinery and the best glues for each application.? Currently all of my joints have been long grain to long grain (gluing up the staves) or I have reinforce the the joint with dowels.?? The key to success is to make sure all grain is going in the same direction.? Though end grain to end grain joints are not nearly as strong as long to long, there are some things I can do to make them stronger… and that just means better, longer lasting drums.? The more I’m learning about woodworking and stave vs segmented designs, I find myself incorporating these finds into my drums.? I thinks its one aspect that really helps my drums stand out and be completely unique…

So after some more research and a generous reply from Malcolm Tibbetts regarding end to end joints, it seems that as long as the grain is going in the same direction, the joint is OK.? Malcolm says the end to end joint will not be as strong as a long grain to long grain, but for most applications it’s OK.? Malcolm is a segmented wood turner who is leading the way in innovation and design using segments and the lathe.? I have a few of his DVD’s and his famous book, “The Art of Segmented Wood Turning”.? I was honored to have him reply to my e-mail, as I know he has lots more experience than I in this field.

Still for my purpose, ie, building functional art (hand drums, djembes, etc.) the joints probably get stressed a lot more than say a vessel that is mostly looked at.? So now that I know the joint is okay.. how do I make it better??? Is there a glue that works best for end grain joinery?

Doing some research on glues, I’m finding that using a polyurethane glue like gorilla glue on end grain joints greatly strengthens the joint.? Because it swells as it cures, it fills the grain and hardens.? The main problem with end grain joints is that the end grain absorbs too much glue, and the fibers are spaced further apart than with a long grain joint.

I read the analogy of trying to glue a bundle of straws to another bundle of straws by the open ends.? Think of using a standard PVA glue (Elmer’s glue, Titebond, most any white / yellow glue) it’s just going to run down the openings of the straw tubes and not give much adhesion.. if any.? Now using a PU glue (polyurethane glue like Gorilla Glue) the glue is a bit thicker consistency, and it expands about 3-4 times its size as it cures.? This fills the holes in the straws and helps to join the two bundles together, while cured it acts more like an epoxy.

I also found that because it expands, a lot of people think it’s good if your joint isn’t perfect, but this was proven false.? You actually need very good joint to get the most from the PU glue, even better than with a PVA glue.? A glue like Titebond II will keep about 80% of it’s strength in a gap up to 1/64 of an inch (.o15) however it is recommended that with a PU glue the gap is no more than 1/256 of an inch (.003)? That’s a pretty tight joint!

I’ll probably still add some dowels to my projects for comfort and knowing that they will add a mechanical advantage, but they are a pain! I keep my wall thickness pretty thick, (5/8 to 3/4 “) and in the case of hand drums, they get thrown around a lot, so using dowels is still a good idea, I’ll just substitute my Titebond for some Gorilla Glue when it comes to joining up end grain.? I’m happy to learn more about the PU glues as I think this will ultimately help me build better drums.?? Remember that PU glue needs moisture to activate.? If your wood is kiln dried or under about 10% moisture, you will want to spritz the joint with water.? If you are joining air dried lumber you might be ok… I’d still spritz a tad of water on both sides of the joint before gluing.

Now for using long grain joints as I do with the main staves for my drums, I’ll stick with Titebond II extended set.? In tests (that I did not conduct) this situation for the glue joints were nearly the same, both being stronger than the wood itself.? A lot of people ask me if I reinforce the joints of my slats.. there is no need to with the glue bonding stronger than the wood.? With a good tight fitting joint, and all the grain going in the same direction, the bond will be excellent and with more chance of the wood failing from natural causes before the glue.? The shell might expand and contract a bit, but it will do so uniformly and the joints will hold.

Wow… unless you are researching glue or an avid woodworker (in which case this might be redundant) this is probably the most boring article I’ve written :)? But after all.. you found it!

I would love to hear others opinions that has first hand experience with PU glue or with end to end-grain joints.