What About Humidity?
It is extremely important to understand the role of humidity in the protection and performance of your mandolin.
Let’s begin with the tree. Just like the human body, the tree depends on moisture—lots of it—for its life. When a tree is cut for lumber, there is a natural loss of moisture as the wood seeks to stabilize its internal moisture with the moisture in the air. Professional woodcutters know that the loss of moisture from the newly-cut tree must be controlled, or the wood will crack badly. With a freshly cut tree, it is a matter of only hours before the lumber will develop serious splits and cracks unless the end grain is sealed with wax or special paint, slowing the moisture loss. The larger the piece of wood, the greater the chance of cracking. Those who cut musical instrument wood, quickly saw the freshly-cut tree into smaller blocks and seal the ends. Then the wood is stacked with spacers between the blocks to allow air to freely circulate and dry the wood slowly and carefully. Control of humidity, temperature, and air circulation are extremely important in drying green wood to a stable, useful piece for musical instruments. It can be done in as little as six months for top wood, longer for the hard woods used in the rest of the mandolin.
Most builders like the wood they use to contain 5% to 8% moisture. That is not the same as humidity, which we describe by comparing how much moisture is in the air relative to how much the air can hold at that temperature—relative humidity. The ideal relative humidity for most musical instruments is 45%. Factories and large music stores try to hold to a 40-50% range. But you and your mandolin don’t live in a factory or music store. Your home and other places you play your mandolin cycle through ranges of 30% (or less in desert areas) to 80% or more humidity. This creates stress in the wood as it takes on moisture and expands and loses moisture and contracts. We are talking about a possible change of some dimensions on the mandolin of up to 1/8 inch! Well-dried wood takes on moisture better than it loses it. So, if you buy a mandolin of properly-dried wood, made and stored at 40-50% humidity at room degree temperature, the mandolin should be fine moving in and out of slightly-more-humid situations, but it can warp and crack moving in and out of significantly less humid situations such as your heated house in the winter, a hot car, direct sunlight—any situation which causes significant moisture loss.
For your own health, you should humidify your house if it falls much below 40% relative humidity. But the mandolin rarely stays home. The best protection for your instrument would consist of a combination of a humidity gauge in your case and a moisture-adding device either in the mandolin or in the case. Where can you find a humidity gauge? The relatively inexpensive digital battery-operated ones are very good, but there are also gauges made for tobacco humidors that look nice in a case. Check a hardware store or tobacco store for one of those. Where do you find moisture-adding devices? Your local music store can get you an “instrument humidifier,” but—very, very important—use it carefully. You can add too much moisture to a mandolin and cause warping, cracking, finish problems, and more. Do not saturate the humidifier and never leave it in the instrument or case longer than a day. A day in and a day out is good for an active player, but no schedule is perfect. Get a gauge and check it frequently.
Many fine mandolins have been destroyed by failing to pay attention to how humidity acts on wooden instruments. Don’t let yours be one of them.