Magazine article Acoustic Guitar

It's Not the Heat, It's the Humidity

Magazine article Acoustic Guitar

It's Not the Heat, It's the Humidity

Article excerpt

If you live in an area of low humidity, your guitar's wood is in danger of cracking and shrinking. A home humidifier will help-but you may also need a guitar-specific unit.

To avoid warping or cracking, guitar woods must be properly seasoned. Most manufacturers dry their wood to an optimum moisture content of about six to eight percent and keep their facilities at about 45 percent relative humidity. These conditions usually produce a guitar that is stable under normal conditions. However, wood is an organic material and susceptible to changes in climatic conditions: In low humidity, the wood will lose moisture and shrink; conversely, in damp climates it will gain moisture and swell. The consequences for your guitar can be dire.


The greatest danger to your guitar is low humidity. Any part of the country that has a "heating season" (or where there are desert conditions) is likely to have low humidity. In the winter in Minnesota (where my shop is located), humidity in homes often dips below ten percent, which can cause guitar wood to shrink considerably.

Low humidity can result in cracks in the guitar's top, although backs and sides can also crack easily. Soft woods like spruce are more prone to humidity problems than hardwoods, although some hardwoods, such as Brazilian rosewood, are more susceptible than others. Low humidity may also cause your fretboard to shrink, which will result in frets protruding from the edge of the board. The most common problem-and in many ways the most aggravating (though ultimately less damaging)-is that the top will flatten out or even go concave, resulting in lowered action and string buzz.

To guard against these problems, be aware of the humidity level in your home (or wherever you store your guitar). Guitar-specific humidity gauges are available from a number of sources, including John Pearse Strings and Planet Waves, and other simple, inexpensive gauges can be found on the Internet. These units may not be accurate enough for scientific purposes, but they're fine for guitarists.


You should keep your home/guitar room at about 45 percent relative humidity. You can humidify your entire house or apartment with a special home humidifier, but often this is not enough. In most winter climates, moisture in the air will condense on the cold windows at around 30 percent relative humidity, and the room will not get more humid than that. At this point a dedicated guitar humidifier is required, and there are several types available. I prefer the kind that covers the soundhole, keeping moisture inside the guitar's body, but others will do the job if they're kept with the guitar in a closed case and are moistened on a regular basis. Check your humidifier every two or three days (you do play your guitar that often, don't you?). If you keep your guitar hanging on a wall, soundhole and room humidifiers are especially valuable.

Be careful not to overfill your humidifier, especially soundhole models. You don't want water dripping into your guitar because it can lead to unsightly staining and, in some cases, instrument damage. In especially dry conditions (five to 20 percent), I recommend keeping two humidifiers in your case. A traditional "soap dish" unit (see "Types of Humidifiers," page 86) kept in the peghead area of your case is a good choice for a second humidifier. If your humidity is moderately low (25-35 percent) one in-case humidifier will be enough. Don't over humidify: if the room humidity is 40 percent or more, you can stop using the humidifier. …

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