Does gluing wood together for your first project intimidate you? With the right tools, materials and technique, you’ll find your glue-ups will go smoothly.Wood is a great material to work with as most wood species are easy to glue up. Wood is porous and glue can grab onto it.
In fact in some strength tests, the glue held and it was the wood fibres that broke and caused the joint to fail.
Read more about clamping here. But properly applying glue is also crucial. Here are some tips:
Wet both surfaces
It is important to get even, continuous glue coverage on the surfaces to be bonded, so apply yellow glue to both surfaces when you can. This provides instant wetting of both surfaces without relying on pressure and surface flatness to transfer the glue from one surface to the other. You will, however, have to work fast as the open time for yellow glue can be around five minutes at a temperature of 70O F (21O C) and relative air humidity of 50%.
Now long should the joint be subjected to clamp pressure? The time varies from species to species, with woods that have an even density across the growth rings, such as maple, requiring less time. But in general, the glueline reaches around 80% of its ultimate strength after 60 minutes of clamping. After this, joints can be released from the clamps, but the full glue strength won’t develop for about 24 hours.
How strong is your glueline?
Even if you have used the correct pressure, it is still reassuring to make sure that you are achieving well-glued joints. A simple test is to place a sharp chisel exactly on the glueline, and strike it with a mallet.
A weak joint will split in the glueline, either because the glue was too thick or the glue didn’t penetrate the wood correctly. The percentage of wood failure will be very low or nonexistent. A good joint will split mostly in the wood adjacent to the glueline.
Use enough glue
The mistake most beginners make is not using enough glue and not distributing it evenly. Then what you end up with is what is called a starved joint.
With not enough glue, you have voids and places where the wood simply doesn’t bond together.
You basically want a thick enough coat of glue so that when you apply clamping pressure, you get a bead of glue squeezing out consistently along the length of the glue-up.
The best way to find out how much is too much or too little is to experiment. Grab two pieces of scrap wood, apply glue to both surfaces and clamp it up. Check to see what kind of glue bead you get.
Too much glue will mean that you get huge drips of glue.
Too little means you won’t see that consistent bead.
Apply glue also requires using the right tools. In a pinch you can use your finger to spread the glue, but I wouldn’t recommend getting used to doing that. When you move to other glues you might be tempted to do the same but with stickier results.