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Loose top on a Yamaha 310

Q: I have a Yamaha 310 with a loose top down at the end opposite the neck. There is about 1/32 crack where top has come unglued or popped loose. I bought it used and was wondering what would have caused this to happen. Can I just glue it down and will that be Ok or is there some other hidden problem?

Harold in Tennessee

A: The factories making guitars try to use as little glue as possible. If they use too much they have "squeeze out" which makes the inside of the guitar look sloppy. Working on the outside of a guitar, glue will not stick to the finish and squeeze out (from the bridge, for example). It can just be wiped off.

The inside of the guitar is bare wood. Wiping at the glue just spreads it around. You have to wait for it to dry and then chisel it off. Sometimes as little glue as possible is not enough to do the job and the joint fails. It may hold for years and then let go in response to impact or high temperature. You must clean the joint. Remove anything that is keeping the joint from closing perfectly: old glue, splinters, '57 Chevys etc. Gets lots of clamps and cauls. Lots of firm steady pressure is better than one crusher clamp in the middle of the crack. Dry clamp to make sure everything fits. Put a good bead of glue on the crack and then open and close the crack to pump the joint full of glue. Put your clamps on and let it dry overnight.

Your guitar was originally put together with polyvinyl resin (white glue). Titebond and Elmer's Carpenters Glue (aliphatic resin) are more popular with today's luthiers. White glue melts at 120 degrees, Titebond melts at 250. Either will work fine for your project. Clean up with water.

Steve Mason