Believe it or not there are some definite tricks to gluing parts of the guitar correctly. If you get too much glue on the wood guitar parts, it will at a minimum, give you a messy cleanup chore and possibly a poorly glued or structurally insufficient joint.
Glue is intended to act as only a very thin film that will hold the two pieces of wood together. In softer woods, there will be some penetration into the wood fibers and the adhesion actually extends into the wood in those instances. This does happen to a smaller degree with harder woods as well.
How Much Glue Is Enough?
Quite often the person doing the gluing, figures that if a little is good, than more should be better. That is far from the truth. The goal is to get the quantity of glue perfect. Follow these tip for good joint results.
Titebond or Other Instrument Glue:
The best way to apply Titebond is to place a bit of glue in a dish or on a piece of waxed paper and apply it with a very small stiff brush. Usually these can be the tin-handled brushes obtained from the local hardware store. Spread it with care not to get any glue on another part of the wood other than the joint. OK – try to. Make sure to apply glue to all surfaces that are to be glued together.
Spread the glue film over both pieces of wood as evenly as possible. This is most easily accomplished by rubbing the two pieces back and forth until you can feel a bit of resistance – that means the correct amount of glue has been applied to the joint.
Titebond cleanup is really quite easy as long as it is cleaned at the right time. The window of opportunity is not that large so be very attentive to the glued area and test it constantly. With experience you will know exactly when to return to the wood to easily peel off the glue. You know you have it right when the excess glue comes off like putty with no liquid squeezing out the the squeeze-out and also, also it is not too dry that it has to be chipped off.
5 Minute 2-Part Epoxy:
The biggest trick with the 2 part epoxies is to get the quantity of the resin and the hardener exactly at a 50/50 mix ratio. If too much resin is used, the glue won’t setup properly. If there is too much hardener the glue joint won’t be as strong as it should be and will be very brittle.
Key to proper mixing is to stir the two parts REALLY well. You can tell if you have it stirred well enough by the color of the mixture. It will turn a whitish-creme color. Also if the epoxy is mixed in a small plastic or paper cup, you will be able to feel the glue heating as it is going through the chemical reaction of setting up. With 2-Part Epoxy, do not glue too much or too many pieces at one time.
To apply the Epoxy I usually keep some small pieces of maple veneer around for this purpose. Dip it into the mixture and slowly spread it on the joint. Now take the edge of the veneer (the edge should be cut square like a knife edge) and slowly spread the glue over the wood surface. It will glide just like a trowel and the glue will cover a surprising amount of area.
As with the Titebond Glue, make sure the glue film is spread evenly over both pieces of wood. This is most easily accomplished by rubbing the two pieces back and forth until you can feel a bit of resistance – that signals the correct amount of glue has been applied to the joint.
Epoxy cleanup is a bit more tedious than the water-based glues. Once it starts to get stiff most of it can be cleaned off with a very sharp chisel. There will still be a residue left on the wood after this and lacquer thinner can be used for the final cleanup. Sight down the wood as you look into a light source and you can see any residue left because it will be shiny.
The smoother and better the joints that on the wood that is to be joined, the less glue will be needed.
In gluing exotic woods, be sure to use acetone to thoroughly clean the resin from the wood to be glued. The use of rubber gloves and a respirator is manditory to protect your hands and lungs. Rub with an acetone soaked rag until no more color comes from the wood.
Slow Set 2-Part Epoxy:
The only difference between slow set epoxy and the quickset type is the setup time that is available. It is extended to at least 30 minutes with full bond strength at 8 hours and overnight is even better. All other things we talked about with the 5-minute Epoxy apply to the slow set.