It is only creatures of the animal kingdom who find high humidity hard to bear. Acoustic instruments are uncomplaining. However, acoustic guitars react badly to low humidity and in case of continued low-humidity conditions can crack at various places, or, in extreme cases, come apart completely.
The most common of such places are the joints in the neck of the instrument, the top and the bridge, as seen in the photograph above.
It is also not uncommon to go to bed with the guitar in perfect condition and wake up the next morning to find one of the joints in the neck having developed a crack, exactly what happened to this poor instrument that I tended to recently.
The owner told me that the night before he was playing the guitar but when he woke up he found the action on instrument alarmingly high. As he went about inspecting the instrument, he found the scarf joint on the neck had opened up.
Thankfully, he had the sense to loosen all the strings and take the tension off the neck. When I got it, I had to tighten the strings beyond full tension to get the crack open wide enough to push glue into.
But here came the problem. The surface of the fretboard over which one jaw of the clamp would sit, was flat enough for the purpose, but how do you get the other jaw to hold tight the curve of the neck?
What followed was a fashioning of a neck caul out of two pieces of wood glued together and then carving the piece of wood so that it could support the neck. Do notice the cork, stuck to the surface to protect the surface of the neck.
With generous amounts of glue forced into the crack, the next thing to do was to clamp the joint together, take the strings off completely, and leave it untouched for a couple of days.
The owner also complained that the bass strings had a tendency to buzz every now and then. While working on the guitar, I noticed that the slots cut into the cheap plastic nut were way too deep. So, out went the plastic nut and in its stead came in a swanky bone nut.
In a couple of days, the clamps were taken off, the guitar strung up and handed over to a happy owner.
To read more about humidity and how to tackle it, enlarge the following picture.