water damage/puckered back seam on Martin J-40

[Dave Richard]

I have this guitar in for repair.  The Oasis humidifier let go inside the instrument, and the puddle sat on the inside of the back.  The back seam is puckered and distorted out( the back strips had curled away, and I've removed the loose ones).  I've been wetting and clamping the areas between the braces, attempting to reflatten the seam.  So far, not much success.  I think I may need to heat the area from the inside(enough to make it pliable, but not enough to damage the finish)before clamping.  Anyone dealt with this situation before? These Oasis humidifiers seem to be little time bombs!

[Demetry Merkuloff]

I had a Martin OM28V in for repair, the guitar had been left too close to the heater for one night. The back strips were loose, the inlay was damaged, the braces were loose, the back wasn't warped so much though. I removed what's left of the inlay strip and the back strips inside, which alowed me to reflatten the the seam and to reglue it to the braces. New inlay, back strips glued back, back refinished. It's a major and costly repair case but I think you need to remove the inlay strip to give the halves of the back freedom to be reflatten, it's easier to correct the gap width for the inlay, than to force 2 glue joints, 2 warped rosewood pieces and the multi layer inlay strip back into their place, all 3 swollen from watering. Martin sell inlay strips in their 1833 Shop for $6 (2 pieces).

[Andrew]

Good to know this about those humidifiers. I always opted for the ones the clip on the inside of the case rather than hang in the guitar.

I think you may have difficulty getting this flat without ungluing the braces and letting it dry out a little. Adding more water probably wont help because thats what caused the wood to expand and result in the ridge you have now, and you cant get water to the finished side to balance it out. Prehaps clamp it up (with caution) somewhere warm at the normal humidity range and let it sit as long as you are able to see if it will start it back towards the original shape, maybe that will get it close enough that you wont have to unglue the braces to get it back to normal.

Edit: had to mention I love your shop. Its nice and homey, and so bright compared to my field stone cellar lol. I dream of a workbench under a big window like that, especially in the winter.

[Dave Richard]

Thanks for your replies. I'm having moderate success removing some of the puckering, by heating and clamping. The trickiest part is figuring out how to clamp those areas not directly under the soundhole. It may prove fruitless. My priority, with this instrument, is to make a good structural repair, with adequate cosmetic results: this guitar, while being played regularly and heavily, has not received the best of care by it's owner. He did not notice that this damage had occurred sometime in the past...
Andrew, thanks for compliments on my shop. After working almost 20 years in a rent- free, but marginal space, I built this one, at home, over a two year period( while working full time in the old space as a cabinetmaker). I wanted lots of natural light, 10' ceilings, and a wooden floor. It's a great workspace.

[Demetry Merkuloff]

Ah, clamping! Another benefit of removing the inlay strip is that you can use some bolt & nut clamping system to gradually put the back halves into place. Otherwise, you can try really strong magnets (worked for me a few times) though I can't say how much resistance there is in the warped rosewood there. If the "curb" is really stiff any clamping won't help much without additional measures (I used small silicon heating blankets in one of the cases like thatt) and I'm not sure the finish can be saved then :(

[Andrew]

With some props insude and cauls to spread the load, you may be able to clamp from the outside. Id be inclined to try that before taking too much apart. Except youll need about 6 hands :S. And of course there is no guarantee that that will flatten things out enough.

[Robbie Collins]

How about loosening the braces, laying the guitar on its back on a flat, stiff table, and using bar clamps on the sides to force the center flat? Then reglue braces using jacks.

[Andrew]

I like it. I still cant see getting good results without loosening the braces in this case. Theyre keeping the warped area from flattening out the same way rafters do in a peaked roof

[Dave Richard]

The repair has gone well. I was able, with mild heating, and shaped cauls to remove almost all the distortion, and reglue the braces.  It's not like new, but it's very good. The double layer of plexi, in the third photo, helped put pressure over the length of the seam.