Caved-in plates

[Jerry Hoffmann]

In the span of one week I had two ukuleles--that were built and sold about two months ago--come back to me, one with a caved-in back, the other with a caved-in top and back. Both of these instruments had the normal arch I put in my plates, and the bracing is on the stiff side for the backs. One is a concert size resonator with a thicker than usual back, the other is a tenor with a thinner back. One is koa, with a lacquer finish, and quarter sawn spruce bracing; the other is mahogany, with a varnish finish and the same bracing (but possibly different stock). What could have caused this? Are the luthier Gods mad at me? One symptom I noticed was that the lacquer finish was sucked into the topography of the wood figure even though it was allowed to dry three weeks before it was sanded and buffed. Is this problem reversible?

[Jerry Hoffmann]

They were at different locations, but both were within 50 miles of my shop. Another symptom is slightly exposed fret ends on one of the instruments. One of them was kept in a studio along with about 20 other instruments and I assume they're all okay. Why it happened is still a little bit of a mystery to me.

[Jerry Hoffmann]

Bob, I understand what you're saying, but maybe the general rule about cupped plates doesn't apply here. I hope not, because I sure don't want to cause more damage.

[Bob Webster]

Hi, Jerry. The exposed frets is another indication that the instrument is experiencing overly dry conditions, or had before it came back to you. The fingerboard is shrinking back and leaving the frets long. I had the same thing happen to me with a couple of instruments and so I switched (reluctantly) to epoxy for gluing the fingerboard.

I'm starting to wonder if both of the instruments went to very dry environments. It may all come down to that rather than conditions or practices in your own shop. You seem to be perfectly aware of the need for controlled humidity and temp in your workspace. You might want to make enquiries and, in the meantime, just leave the instruments out in your shop to equilibrate for about a week and see if they come back into shape. If they do, lI'm sure you could find a cat'o'ninetails on eBay and apply it appropriately.

Bob

[Jerry Hoffmann]

Here's an update on this problem. After more than a week of adding moisture to the wood through the use of a guitar humidifier, the backs of these instruments have slowly returned to their original arch and the finish is once again smooth and level. The owner of the koa tenor checked the humidity in his studio and it was 20%! He owns several nice guitars that seem to be okay, but didn't waste any time installing a humidifier.

[Bob Webster]

Wow, Jerry. Happy ending. Bet you're pleased. Did you pistol-whip the owner or were you properly controlled?

Cheers,
Bob