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Greetings. Lurker, occasional poster here. A current project is a 1930 or thereabouts OS Stella Grand Concert, poplar neck, spruce top, birch faux RW body. I obtained it several years ago, largely intact, however with a severe neck bow and pin bridge dislocated - slid apparently from tension and heat softening glue... The frets are very sharp - as neck is shrunk, and there is a center seam separation. I have had the guitar in a small closed room with humidifier running for about 2 weeks, with some positive effect on the top - small crack closed but center seam not, and no effect on the neck. It apparently does not want to absorb moisture.

I then put it in a closed case with a wet sponge,  and after 4 days the sponge is still wet.

Is this guitar pernanently shrunken and dry?

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 Frank, if you were hoping that the fret ends would retuck themselves in, it is almost impossible that they will.  Once a neck has shrunk, it is almost impossible to get it back to original spec. You need to file those fret ends. As far as the centre seam crack, I think you will have to splice some wood in there and be done with it.

 Just my opinion though!

I recently went through this exercise trying to close a long new crack. The sponge in the case didn't seem to do very much. You should reference the recent post on the 70s J55. I hung the guitar with a garbage back around the body, a soaked automotive sponge in the bag.(as described by Hesh). It really worked, but this was recent damge. As someone pointed out, old damage may not be reversible.

Also, the materials in your old guitar might not have been seasoned properly long ago, and what you're trying to reverse is "congenital".

Yeah all bets are off when an instrument has been dry and cracked for years.  Even if you do get positive movement over time dimensional instability can take a "set" and then she is what she is.

Cool guitar though!

PS:  The bag method will bring RH to around 75%ish so it's a bit more of a heavy lifter than a humidified room or case.

Just had another thought too after I posted.

We've been discussing Torrification on another forum which is basically a process similar to how charcoal is made... and pre-treating wood stopping hopefully before the charcoal point...;) in an effort to change the material at the molecular level hopefully making it more stable and resistant to dimensional changes and instability that is more commonly seen in wood not seasoned much if at all.  The proponents see a fast track to vintage tone without the wait and other proponents such as Gibson see it as a way to use less expensive materials such as maple for fret boards now with a dark, ugly color.

Me?  Jury is out but personally I'm not inclined to want to have to refret a charcoal briquette...

Anyway if the argument for torrification and even baking tops is valid that the cells shrink at an accelerated rate because of these processes hence reducing the amount of water that can be absorbed by the wood when exposed to higher RH it also stands to reason that older, seasoned instruments are going to respond a bit less to efforts to humidify them.

Yes, no?  Am I making sense here?

I think you have already received good responses but I want to add that, in my experience, it's not all that uncommon to see center seams that open and will not easily close again on old, lower end guitars. I think that the seams may not have been so perfectly straight when they were glued up and the open is partially a result of the wood springing back after the glue failed. They just don't close with humidity and will need to be splinted.  I've clamped them back but had trouble keeping them closed. My most recent experience was a crack I closed with clamps that popped when the humidity suddenly lowered in my area. The glue held but the fibers next to it didn't.  I splinted the "new" crack and everything is fine. 

Sometimes you have to accept that option and learn to do touch up on the color and finish. 

Thanks all. I will try the bag humidification procedure. I checked today and there are indications that the case treatment is slowly working also to some degree.

As you can see I have the bridge fastened with bridge bolts, and have it tuned to open C, since the bridge plate has some string-ball wear and also want to see how it holds up. I can play with a bottleneck and it has a wonderful tone, even as-is. I tried doing a heat press and it made only a slight improvement. Pretty sure it will need carbon fiber rod and neck reset. The center seam could use a spline, r maybe I'll just fill it with gorilla glue (inside joke). It's actually a pretty desirable guitar in some circles.

Re the pst above about treating wood, I often wondered why not just periodically treat the unfinished interior guitar wood with some type of oil to keep it from drying out...though would likely have some effect on tone...

For all that I'm one of the ones usually recommending it, I actually hate humidifying a guitar. It really tries my patience because it seems to take for-ever-er and when I say that I mean weeks!

 It really can help a lot but, like Kerry said, it probably won't do much for the neck. You said that the neck bow is "severe" so it may not help you much but something I've done successfully is remove the fingerboard and plane the neck flat again before adding some reinforcement. It works pretty well but only because the neck was not too badly bowed. I like graphite but one of the guitars was an Kay archtop that already had a  square steel rod. It wasn't as straight or flat as it should have been but with a little attention it works fine now.  

Rehumidifying an guitar is not intended to do anything for the neck, it's a body in a bag so-to-speak.

In my experience some instruments can respond in as little time as a day and others may take a week but we have never had to bag one longer than that.  It could be that how we bag em and how you bag em are not the same method.  We try to make sure to have approx. 6 - 8 ounces of water in the bottom of the bag and the sponge.  We also maintain a strict 42 - 48% RH in the greater shop and we use calibrated standards to ensure that our hygrometers are accurate or close to it.

In Michigan it's now warning up a bit so some instruments are recovering simply from the furnaces being on less, less dry air in the home, etc.

Bagging as you do is probably a lot more efficient than a sponge in the case. Next time I'll try it your way. 

Frank one thing to consider when considering applying any kind of finish, oil, etc. to the inside of the guitar is that it may make it more difficult to service in the future since glue does not like finish,oil much.

Also I suspect that any potential benefits of finishing the inside are short lived in that eventually it's going to dry out anyway if it's in a dry envirnment.

Thanks. No I don't expect that the humidification will straighten the neck. Objective was to somewhat get the frets ends retracted and, playing on the moisture theory, perhaps enable another attempt at a heat press and mini reset as per some reading on the subject. Considering how much shrinkage occurred on the poplar neck/fingerboard - as judged by the fret end protrusion - the guitar has otherwise stayed together quite well.
I want to report that the guitar has been tuned to open D and kept in case with sponge for about a month. Its holding in tune, heat press seems to be holding and the top cracks have closed quite well, though not glued and cleated yet.

The center seam below the bridge, which is fastened only with 4 stringbthru bridge bolts has developed a peak, so a straight edge placed below and parallel to the bridge will teeter (not Don).

Is this an indication that a brace or other member has failed, or just because the bridge is not glued down? Is this typical failure mode of ladder braced guitar top? Thanks.

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