The Effects of Temperature and Humidity
Every guitar is made of wood. Acoustic guitars and basses have thin wood tops, sides and backs, while electric guitars and basses have much thicker wood components.
Wood is easily affected by temperature and humidity. The ideal temperature and humidity for a wooden instrument is 45%-55% humidity and 72-77 degrees. If either humidity or temperature, or both, vary greatly from these conditions, your instrument can be affected and, in some cases, permanently damaged.
A rapid change in temperature or exposure to extreme cold can cause small cracks in the finish. These are lacquer checks. Cosmetically heartbreaking, but not fatal to your instrument. If your instrument is exposed to freezing temperatures, let it warm to room temperature before removing it from its case. This can take a few hours and allows the instrument temperature to increase more slowly, decreasing the possibility of finish cracks – or worse, actually cracks in wood.
Another temperature problem can arise during winter months. Avoid hanging your instrument on a perimeter wall of the house. The wall temperature may be much cooler than the air inside the house. The difference between these temperatures will cause the top and back to have different temperatures, and may result in damage.
You also need to prevent rapid changes in humidity. If, for instance, you hang your instrument near a source of dry heat such as a wood stove, the humidity will drop much more quickly than naturally occurring changes. If the moisture content of wood is forced down rapidly, there is uneven shrinking from loss of moisture content. This can cause cracks and open joints.
As humidity increases, the moisture content of wood also increases, causing it to expand and swell. A gradual increase in humidity generally will not permanently damage your instrument. However, when very high humidity is combined with high temperature, glue joints can become weakened and may even open, weakening the joints. The glue under the bridge can be weakened to the extent the bridge pulls away from the top.
You can help control humidity two ways. We strongly recommend that you keep your instrument stored in its case – and - use a humidifier that is designed to provide moisture (but does not allow moisture to come in contact with your instrument).