Top and back are warped

[sfeatherston3]

Well everyone said not to do it, but I did: my garage/shop, despite having a portable air conditioner, had some crazy humidity fluctuations in the last few months. Now my top is bowed up (really bad over the lower bouts). If you put the top on a flat table, rosette up, the bouts are warped up. Worse, the back is warped in the opposite direction that it should be curved. It warped back so hard that it split one of the braces down the middle about 4 inches (the glue held though- yay!!)

The humidity in the garage, a few months back, wasn't controlled by the a/c. The thing has some sort of "no drain" technology that apparently doesn't remove any moisture from the air (or returns it somehow) and the humidity got up to the high 70s %. Worse, when it got cold the heater (built into the same unit) DOES drain water and quite a bit of it (guess it has some sort of built in heat pump). Coupled with the already dry, cold air, the heater pulled the humidity down to 28% at one point. This is all assuming the cheapo digital weather station in my garage is reporting accurate data.

I braced the top and back in late July and due to various life events had to put construction on hold until recently. That is when I discovered the terrible warping.

I have some questions for you guys:

1. Was it the humidity variations that caused the damage or the length of time that I left the top and back laying in a cardboard box without putting the whole body together? Or both?

2. Is there anything I can do to return the top and back back to their original shapes, or do I scrap everything and start over? I did throw some glue in the split back brace (it was the longest one near the tail of the guitar) and clamp it back together- guess I'll have to see if it holds.

Thanks,
Sam

[tippie53]

sounds like humidity . Let me ask you this , do you know what the RH was when you glued up the bracing ? It sounds like your RH dropped and that caused the issue . If you set this back into an RH that resembles the glued rh it should come back. The worst case scenario will be to pull off the braces are re brace the top and back.

[Tanazzo61]

Hi, I read somewhere, that when you have humidity problems in your laboratory, it's better to spent a whole weekend or 3 or 4 days in a row to brace the top and back and quickly close the box, so once the body is closed, it's more difficult that it warps. To repair the damage, try to disassemble all the braces with some kind of heat, and put the top and back under a flat weight after you sprayed it with water. I never did that before, maybe it works.
Good luck.
Gaetano Mascaro

[tippie53]

closing a box won't stop a top or back from warping if the rh changes . You can't stop physics . Top and backs will sink when the RH drops in relation to the RH condition at the time of glue up. As the RH drops the wood will shrink across the grain. The braces will lock the top and as the top stressed against the bracing this will pull on the braces and like a bow it pulls and this will reverse the curvature of the bracing as the grain shrinks the top will sink and stress will build until the top or back will crack. .

[Ben-Had]

closing a box won't stop a top or back from warping if the rh changes . You can't stop physics . Top and backs will sink when the RH drops in relation to the RH condition at the time of glue up. As the RH drops the wood will shrink across the grain. The braces will lock the top and as the top stressed against the bracing this will pull on the braces and like a bow it pulls and this will reverse the curvature of the bracing as the grain shrinks the top will sink and stress will build until the top or back will crack. .

Absolutely correct. And as proof - I left NC to go to NY to be with my son who was in a M/C accident, I was there for a week. We had a (and are still in) a cold snap and the RH dropped from 46 to 21 in my guitar room while I was gone. Didn't have the humidifier on and honestly forgot to tell my wife to do it. All but about 2 of my guitars were unplayable and the action was so low on those I could barely play them. Two days of running it on high/high has got it up to 40 and the guitars are coming back. Whew, watch that RH folks.

Tim B