Protecting Your Guitar from Excessively Low Relative Humidity
The most common problems with acoustic guitars are caused by low relative humidity. Exposures at any rates lower than 37%, relative to 24°C for any period of time will very likely result in damage. Damage caused by dryness usually requires the prompt attention of a competent repairperson and can be much more serious than damage caused by excess humidity. If you live in an area that tends to have harsh winter weather, make sure to note the following potential problem areas:
Low action: One of the most common winter weather problems is string buzz resulting from low action. As the neck and fingerboard shrink due to loss of moisture from the wood, the frets (being impervious to humidity changes) force the neck back. As the top flattens out, the string height lowers and buzzing may occur up and down the fingerboard. This buzzing is usually a warning that you should humidify your instrument. In extreme cases, cracks in the top along the sides of the fingerboard extension may appear.
Exposed frets: If the fingerboard continues to shrink due to dryness, frets will protrude from the sides and may even catch on clothing or cut your hand. While a repairperson can file off the excess, you should take action and humidify your guitar before other more costly problems develop. The use of any kind of oil, silicone, or wax products on the fingerboard is not recommended. With constant playing, oils from your fingers should be more than sufficient to keep the fingerboard from cracking.
Arch changes: Excessive dryness will cause a change in the arc of the back and top. We build our guitars with the top and back slightly arched and as the wood becomes dry and shrinks the top and back can become flat, or concave. At this stage the finish may appear to ripple. This distortion is actually caused by the wood shrinking beneath the finish. However, returning humidity to normal levels should correct this problem.
Distortions in finish: If the back and top continue to shrink, you may also observe the center seam slightly open. Although this is not in itself serious, it can leave permanent marks in the finish. You may also notice a gap appear around the purfling and rosette. As the wood shrinks, it draws away from the more impervious materials causing a slight separation. This gap unfortunately will not disappear when the humidity returns to normal, but this will not affect the life or playability of your guitar.
Bridge lifting: Excessive low humidity in winter can also cause the bridge to lift. The grain in the bridge runs perpendicular to the grain in the top. Because they are made from different species, these parts will expand and contract at different rates, and as they shrink from loss of moisture due to excessive low humidity, the bridge will actually separate from the top with a shearing action. This is quite easily repaired by a competent repairperson, but is not covered by warranty.
Back and top separation: The same tension as occurs with bridge lifting can occur as the back and top shrink against the struts in opposing directions, causing them to separate. This may result in a buzzing noise from within the acoustic chambers of the instrument, as well as a structural weakening of the guitar. The back is more likely to suffer from this problem, as glue does not adhere to rosewood quite as strongly as it does to spruce. Repairs of this sort can become quite costly and are not covered by your warranty.
Body cracks: A more serious problem associated with excessive dryness, is that the top, back and sides are likely to crack as the relative humidity dips below about 35%. To repair these cracks and subsequent damage to the finish, a repairperson must re-humidify the instrument, glue the cracks, and re-spray the top. This is a time consuming and costly repair not covered by your warranty.
A good Hygrometer (A device used to measure the moisture content in the air) and Thermometer (A device used to measure temperature) are good investments for monitoring relative humidity. Placing them near your guitar or in your case will give a good indication as to the relative humidity surrounding your guitar. In addition to using these device, make sure to visually inspect your instrument on a regular basis to check for the above types of damage. Should you encounter them, it is highly recommended that you take the guitar in for repair and identify an alternative location in your home for storing the guitar.
