Guitars and Humidity. The Ongoing Battle
I’m sure you’ve heard the saying “an ounce of prevention is worth a pound of cure”.
I can’t think of a better example of this than guitars and humidity. When a guitar is exposed to high or low levels of relative humidity, the woods absorb or release moisture to achieve equilibrium moisture content with the surrounding conditions. This is one of the natural laws of wood and has been driving guitar makers and repairers to distraction forever.
The effects of low moisture levels in guitars are quite well known; low actions, protruding fret ends, and even soundboard splits are common when a guitar is exposed to very low humidity conditions for anything more than a few hours. The effects of high moisture levels on a guitar are probably less well understood. They include raised actions, swollen soundboards, sunken fret ends and a host of other issues, most of which impact the playability and tone of the instrument.
In most of these situations, the effects can be reversed to a degree with prolonged exposure to ideal climatic conditions (45 % RH and moderate temperatures, say 22 deg Celsius). This obviously does not apply to splits. They need to be repaired. This reversal is not complete either. There are usually a few residual issues that require a skilled repairer to resolve.
This is because wood has a “memory” and there is an effect known as hysteresis which means that even though the moisture content in the wood may revert to “ideal”, the cellular structure of the wood will have altered to some degree and maintain the “new shape” despite the change in moisture content. To reverse this effect involves taking the instrument beyond the target point (in the opposite direction) for a certain time and then letting the wood settle to its ideal setting. This is call reconditioning in wood drying parlances and, though fascinating, is way too complex for this discussion.
So, given all that, the best way to avoid all this heartache and trauma is to not let it happen in the first place.
Up until now this has been quite difficult and probably beyond the resources and knowledge of the average musician. This is where Boveda comes in. Boveda have created a product that sits in the case with the guitar and controls the moisture levels in the case environment by absorbing excess moisture or by releasing moisture in dry conditions. We have selected their 49% relative humidity packs and tested them extensively.
The easiest way to measure movement in moisture levels in a guitar is by weight.
Guitars can absorb or shed up to 20 mils of water depending on ambient conditions. We put two guitars through a variety of intense conditions, from hot and dry, to hot and super wet, as well as cold and dry, and cold and damp. Both guitars were in cases, one with three Boveda packs, one without.
These were conditions we would never warranty a guitar through, and frankly, we expected them to show severe signs of stress after their ordeals. The guitar with no protection experienced a weight fluctuation of 14 grams, the guitar with the Boveda packs fluctuated by 7 grams. The guitar with the Boveda packs required no adjustment and action height and playability remained constant. There was some movement on the second guitar which required setup work to rectify.
