How does relative humidity affect guitars? Wood will try to equalize to it's surrounding air, in temperature and humidity. If wood becomes too moist it will swell; on the other hand, if wood gives up it's moisture, it will shrink. All are physical characteristics of wood.
What is the desired level of humidity? 45%-55% relative humidity is optimum. If this is obtained, you minimize the risk of damage. This is the relative humidity the Martin Guitar factory maintains.
What if my guitar has been subject to excessive humidity? If your guitar has been exposed to excessive humidity seams may separate, bridges may become loose and your action may become unplayable. A dehumidifier is recommended if your guitar has seen these changes.
What if my guitar has been stored in a dry environment? Low humidity seems to be more of an issue. As your guitar dries, the wood actually shrinks. This results in the top lowering and the strings come with it. All of this stress results in the wood cracking. To solve this problem you should invest in a humidifier. Be sure to also get a hygrometer to measure how much humidity you bring into the air.
What happens to my guitar at 60% humidity? At 60% relative humidity or above symptoms may include tarnished frets and strings, corrosion to nickel, chrome or gold plating on tuning machines, swelling of the top, high action and loose braces and bridges.
What happens to my guitar at 50% humidity? At 50% relative humidity your guitar is in good condition.
What happens to my guitar at 40% humidity? At 40% relative humidity you may see sharp fret ends. This is the area of the fingerboard that extends over the body that may begin to crack slightly from the 12th or 14th fret toward the soundhole.
What happens to my guitar at 35% humidity? At 35% relative humidity your top will begin to shrink. The soundboard may look and feel rippled or dried in. The sharp fret ends seen in 40% relative humidity will become more evident.
What happens to my guitar at 30% humidity? At 30% relative humidity you may see cracks in your guitar. Even if you do not see a crack in the guitar, it has still lost moisture and the top has begun to sink. To make your guitar playable you may need a higher saddle.
What happens to my guitar at 25% humidity? At 25% relative humidity more cracks are seen. Fret filing may be needed.