Are you doing it right?
A thorough understanding of humidity and how it affects guitars is essential to guitar care and maintenance. Your high-end acoustic guitars are at risk when your humidity becomes excessively low or high.
So how does relative humidity affect guitars?
Every organic, porous substance tries to equalize to the surrounding air, both in temperature and humidity. Wood also equalizes to the surrounding conditions. When wood takes on moisture, it swells, and when wood gives up moisture, it shrinks. This is a physical characteristic of wood.
Forty-five to fifty percent relative humidity is considered optimum for effective preservation of wooden objects like guitars. If the humidity where you store your guitar stays around 45% relative humidity, you minimize the risk that your guitar will become damaged. At the Martin factory, they maintain a temperature of 72° Fahrenheit and a relative humidity level of 50%. They believe that if these levels are maintained where you store your guitars, then your instruments will benefit by remaining stabilized and close to factory specification.
What Can You Do?
Guitars will display symptoms of improper moisture content, and these symptoms can be detected. Remember, just because a guitar has not yet cracked doesn’t mean that it is in good condition. Use the information below to determine the condition of your guitars.
Keeping a watchful eye on your guitar inventory will help you maintain proper humidity and keep your guitar stock in perfect shape.
Low humidity is usually more of a problem. The guitar slowly dries, the wood slowly shrinks and the top slowly lowers, bringing the strings along with it. With no other way of relieving the stress, the wood cracks.
The obvious answer is to use a humidifier. The largest problem lies in determining how humid you should make the air, so you will need a hygrometer to measure humidity. Hygrometers are available in various price ranges with less expensive models sacrificing accuracy. For players with extensive inventory, a professional humidity monitor is probably more appropriate.
Guitars that are exposed to excessive humidity begin to swell. When they reach their limit, seams separate, bridges become loose and action is unbearable. Humidity can be subtracted with a dehumidifier. In the summer, when it is humid outside and you air-condition your home, you are in effect dehumidifying your home. In some areas additional dehumidification may be required, and there are desiccant and refrigerant varieties of dehumidifiers available.
Typical Effects of humidity changes on guitars
At 60% Relative Humidity or Above
High levels of humidity can be detrimental as well. Typical symptoms are tarnished frets and strings, corrosion to nickel, chrome or gold plating material on tuning machines, swelling of the top and other wood components, high action and loose braces and bridges.
At 45-50% Relative Humidity
All guitars are in good condition.
At 40% Relative Humidity
Guitars may begin to show sharp fret ends. The area of the fingerboard that extends over the body may begin to develop a small crack from the 12th or 14th fret down toward the soundhole.
At 35% Relative Humidity
Tops begin to shrink; the surface of the soundboard may look and feel rippled or “dried in.” Sharp fret ends will be more evident.
At 30% Relative Humidity
A guitar may crack, but even those that are not cracked have lost a considerable amount of moisture and the tops are sunken. Often a higher saddle is necessary to make the guitar playable.
At 25% Relative Humidity