I have a Martin DC 16RGTE with the top sinking in…It's sunken a full 1/8th of an inch in front of the bridge…I can find no loose bracing so far…It's in a dry time of year here in Minnesota…Is it possible lack of humidity could do that ?...

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Lack of humidity can do that, just north of you here in Manitoba we get a lot of this kind of thing. You need to humidify your guitar, try to do it slowly, if you do it too fast you'll create more problems. Check to see if the back of your bridge is lifting. 

In a really dry climate like we have here, ideal humidity levels are very difficult to maintain. I used to keep my store at thirty percent in the winter. I did this because I knew that ninety percent of the guitars in my shop were coming from or going to a dryer environment. The extreme changes are hardest on your guitar.

Cool….Bridge is solid…Everything is solid…I'll do it slowly with a lightly dampened sponge in a perforated baggie……My first instinct was to play it while taking a shower…..But I think slowly might be better...

I got a record amount of top cracks and bridge reglues last year…..It was a hard winter in Mn , with a LOT of old time radiators in old buildings that guitars seem to hang out in...

I've seen it before.  I have a "right off the boat new" guitar right now that has a sunken top. I got it very cheap because it sunk almost 3/8th of an inch at the sound hole. Humidifying the guitar brought it up about half that distance. In this case, I suspect that the top wood was dryer than the braces when they were fitted. It seems like the braces were glued in the proper position but are not just a bit short now that their moisture level is closer to the top's. 

I doubt if Martin would make a mistake like this but ....who knows. 

Yep it's dried out and we are seeing these everyday here in Ann Arbor.

The sponge in a baggie is not enough to make a difference in my opinion.  It's enough to maintain an instrument that has not dried out but not enough to reverse a dried out instrument.  Instead what we do is hang the instrument from a hanger and take a large, quality garbage bag with a large car wash type sponge as wet as you can make it in the bottom of the bag.  Raise the bag from the bottom of the hanging guitar and tie it off at the neck/body joint.  The strings should be off too and of course you don't want the sponge or water in contact with the guitar.

Leave for 3-4 days and then see what you have.  I have two here at the moment that I can't get to until Monday because we want them in the bag for at least three days.  Our tests show that the RH in the bag is around 70 - 75% and this rehumidifies the guitar nicely in our experience.

After the thing swells back to shape it needs to be worked on in a decent RH envirnment as well and then of course kept where the RH is suitable for an acoustic guitar and/or in a case with a frequently charged, quality guitar or case humidifier.

By the way if the top has sunk you may be very close to having cracks appear as well, perhaps check carefull for cracks, loose braces, lifting bridge (I read that you checked for this already).

I would especially look for cracks right along the fingerboard extension. Sometimes theyre right aling the f board edge so theyre hard to see and insidious, and a big structural risk obviously.

Hesh I don't  know what it's like in Ann Arbor but I live a handful of hours north of Minnesota. Winnipeg is documented as having the most extreme temperature changes of any major city in the world. 100f in the summer and -40f in the winter. Last winter we saw a whole month where it didn't get warmer than -19f. The rules are different here. If I put a guitar in a plastic bag like your recommending it would start falling apart. It needs to be introduced to a better environment over a matter of weeks not three days.

Sorry to hear about your aweful weather John.  

We've rehumidified hundreds of instruments in the manner that I suggested with never a single issue resulting from the method...  Last winter with the polar vortex decending over Michigan we had weeks of sub zero weather, not a usual thing for us.

When considering any method to rehumidify a wooden musical instrument there are multiple factors that need to be considered.  Not only the degree of RH that the instrument is exposed to but the duration is also important.  An acoustic gutiar left in a 70 - 75% RH envirnment for pehraps a week or more most certainly would be a concern.  But three days or so serves us and our clients very, very well.

Here's wishing some warmer weather on us both!

Having repaired guitars in Toronto for fifteen years and then in Winnipeg for twenty years I actually have a clue what I'm talking about. Contrary to the assumption that i don't. Twenty below in Winnipeg is much dryer than it is in Toronto (four hours from Ann Arbor). Rehumidifying a guitar that quickly when it's dry on a level that we see here can cause serious problems. Rapid and/or extreme changes in humidity or temperature can cause guitars to fall apart structurally on a level I never saw in Toronto. 

I'm trying to give advice that takes into consideration the climate of the place the question came from.

Hi John:  Please know that I appreciate you and your experienced advice and your willingness to share with me and the others.  With this in mind Thank You for your thoughts and experience.

Not trying to argue with you by any means but what we do works for us, works very well, we've never experienced any collateral damage associated with bag rehumidification, and it simply works well, quickly, and consistently.

Please note we are sticklers for how long an instrument remains bagged with perhaps 3-4 days being a max.

Additionally we keep our shop pretty humid all winter long with it usually being at around 48% (verified).

I hear you though and just this past week nearly every acoustic repair client that we saw in our business  which can be a dozen or more acoustic instruments in a single week we ask before opening the case how long has the sucker been in the cold...  As such we are well aware of thermal shock possibilities and it's not unusual for us when an instrument has been in a cold car in 5 degree F weather to suggest that the client go have some coffee and return in an hour so that the case can acclimate to our shop slowly before being opened.

I've never seen it personally but my business partner has seen when a cold case is opened and the finish crazes right before your eyes....  He also said that you can hear this happening....

Being the coward that I can be when it comes to potential liability.... ;) rest assured that we are very keen to be on top of weather related including RH related issues in our repair biz.  We also have invested in not one but three high psycrodyne wet-bulb testing rigs so that we know what we are dealing with.

I appreciate your concern, John, please know this.  But respectfully we do know what we are doing, have a very high volume repair business with lots of experience behind our people.  David Collins taught Lutherie at the Galloup school, worked at Elderly, built hundreds of instruments often as a ghost builder, etc.  I'm the newb with only a decade of experience now and still coming back for more...;)

Thanks though for your concern and lets get past this winter and back to sunny days!

Where do you get your bags, Hesh?

Hey Robbie:  I think IIRC these came from a local Mom and Pop (real) hardware store but I can't recall the brand at the moment.  We've use Hefty bags too with good results but the clear bags let us look through the bag at top cracks to see our progress.

We did some testing with hygrometers in the bag and what works best is something like a sponge, a big one, that is not submerged.  More specifically I was just putting a couple of cups of water in the bottom of the bag but having something that wicks the moisture and then dries out naturally imparting the moisture to the air got us a higher RH level in the bag than just water in the bottom of the bag.

Happy 2015 to ya too my friend!

Here's the current crop basking in the RH....


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