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Repairing concave top on a victorian era guitar

Q: I have a late 19th century nylon string guitar that I am attempting to make playable. It came to me with a bowed neck and a slightly concave top. I think steel strings may have been put on it at onetime. The neck I have straightened by heating and clamping it and replaning the fingerboard a little. My problem is the concave top. It is sunken between the bridge and neck about 3/16" at the deepest point. I have tried to show the damage in the attached photo. how can I persuade the top to return to it's original flatness (or reasonably close) without performing major surgery?


A: Look inside the guitar using a mirror and lots of light. I wired up a tiny 40 watt bulb in a socket with a switch and a plug and lamp cord that I bought at the local hardware store. Be careful not to let the hot bulb touch the inside of the guitar. Lots of light is essential. A flashlight won't cut it. Look for loose braces. If the center of a brace is loose the top bellies up. Loose ends will let the top cave in.

If you have loose braces regluing them will flatten the top. I suck glue into a length of plastic tubing and then blow it into the open glue joint. I then use various jacks and clamps to close the joint.

If you do not have loose braces, major surgery is required to flatten the top. The back must be removed. You make a go-bar deck with cut outs for the bridge and fingerboard. You may be able to remove and reglue the old braces or you may have to replace some or all of them. You might need to remove all the braces and use bags of hot sand to bend the spruce.

People worry too much about whether their top is flat. What counts is the action. If the guitar can be adjusted to play slick, and the joints are all tight, relax and enjoy the guitar. Guitar tops are rarely flat. When the strings get high enough that the guitar gets hard to play, peoples eyes are drawn to the undulations of the top, when the real culprit is probably the neck set.

Steve Mason