Isn't it time for Meadowood to nag about humidity
Mar 2003 -- Every year, Meadowood News includes an article in “Repair & Care Tips” about humidity (or the lack of humidity) in a Winter issue. We do it because instrument dehydration, though damaging, is gradual & unnoticeable until it’s well advanced. We beat the drum because it’s really that important.
Instrument tone wood - though aged in a controlled environment to make it stable - still swells & shrinks with moisture content. For this reason, instrument builders keep humidity in their workshops steady at about 50% so that the wood with which they work doesn’t continually change size & shape as it absorbs & loses moisture. Even after the instrument is complete, relative swelling & shrinking of the wood creates stresses in the instrument.
Spruce & cedar, used in the tops of acoustic instruments, are more prone to moisture exchange than harder tonewoods used for backs & sides (mahogany, koa, maple, walnut, rosewood...). Spruce & cedar are also weaker than woods used in the back & sides (which, when curved & glued onto bracing, are even more rigid). The greater tendency to expand & contract, coupled with lower strength, make instrument tops the most likely place for damage from humidity problems. Small, gradual humidity fluctuations should not cause concern. But large, sudden changes & prolonged dryness represent a grave danger to instruments.
In humidity above 60%, the unfinished wood on the inside of your instrument absorbs water & the wood swells. As an instrument absorbs moisture, the rigid sides hold the edges of the weak top in place and the swollen top puffs outward a little. The swelling tends to raise the strings higher from the fingerboard. Also, swelling compresses the wood & can muffle the instrument’s tone.
In humidity below 40%, wood loses moisture & shrinks. Trying to shrink away from the rigid sides, the top is in tension and can crack. When humidity drops below 40% for an extended period of time or quickly drops a significant amount, cracks can suddenly appear in the top.
Because cracking in dry conditions is so likely, & the problem is preventable, no instrument builder warrantees against it. Therefore, the repair cost for dehydration cracking comes out of your pocket. Depending on the size, location & character of the crack (or cracks), the repair can be pretty pricey – often hundreds of dollars. To add insult to injury, the cracks are sometimes very difficult to fix, & evidence of the crack is often visible after repair – even with a properly done repair. The risk of visible evidence of a crack increases dramatically if the repair is not done immediately & the wood has time to distort or dirt has collected on the crack surface.
What can I do?
In humid periods: keep instruments in air-conditioning; if air-conditioning isn't possible and you note undesirable changes, take instruments to a repair technician for seasonal adjustments.
In dry periods: keep instruments away from heaters; use room - or instrument - humidifiers where you store instruments; take instruments that crack for repair immediately to increase the possibility of complete repair.
This article is part of Meadowood Music’s archive of information on selection, care, and maintenance of stringed musical instruments. Some instrument conditions require professional evaluation and repair.