Humidity And Guitars
Too little or too much humidity can devastate a wooden instrument. Visit any guitar manufacturers Web site, or those of independent luthiers and you’ll see information on how critical it is to keep your guitars, mandolins and other stringed instruments at the proper humidity level. Instruments need to be kept between 45-55% relative humidity. Simply putting them in their cases during particularly wet or dry months will not suffice.
Most acoustic instruments have spruce tops. Here’s what Taylor Guitars has to say about the impact of humidity on spruce:
“Our factory is climate-controlled to maintain a temperature of 75 degrees and a relative humidity of 47 percent. This consistency causes the wood to equalize at a specified moisture content. As the wood’s moisture content changes, so does the size of the wood. Spruce, in particular, shrinks and expands a tremendous amount as it gains and loses moisture. For example, let’s say we condition a spruce top in a room that is 47 percent RH, and then cut that spruce to a width of 16 inches. If we then were to lower the room’s RH to 30 percent, that same piece of spruce would shrink to 15.9 inches in width — shrinkage of almost 1/8 of an inch! If, instead, we were to raise the room’s RH to 60 per- cent, the spruce would swell to 16.06 inches, an expansion of almost 1/16 of an inch.”
While these changes are a fraction of an inch, they are a major change, and a major problem for musical instruments. Damage caused by too little or too much humidity will not typically be covered by most manufacturers warranty plans. Fixes can be expensive and visible. On vintage instruments, certain repairs can reduce the value of the instrument by as much as 50% even after the repair has been flawlessly executed.
What do other guitar builders have to say?
From the Martin Guitar Company site: “Your guitar is made of thin wood which is easily affected by temperature and humidity. This combination is the most important single part of your guitar’s surroundings. Martin keeps the factory at a constant 45-55 percent humidity and 72-77 degrees Fahrenheit. If either humidity or temperature get far away from these factory conditions, your guitar is in danger.”
Martin also suggests keeping your guitar in the travel case where the small space is more easily humidified.
From Larrivee: ”Fully 80% of the guitars returned requiring repair have damage which is the result of severe dehydration. Damage due to dehydration is not covered under warranty because it is owner-preventable environmental damage.”
Too little humidity can result in wood cracks (top, back, sides, bridge, fingerboard, etc…) In dry conditions, the top and back can sink in – pulling at the center seams – sometimes causing them to crack open. Also, as the bridge drops lower, it lowers the action and can cause strings to buzz as shown in the diagram below (courtesy of Taylor Guitars):