Maintaining a Healthy Humidity Balance for Guitars

Follow these steps to protect your wooden instruments from the low-humidity conditions that prevail during the winter months

by Jon Chappell

The "pain points" of a guitar that are most susceptible to changes in relative humidity. Diagram courtesy Taylor Guitars.

The winter months usually spell wet misery for many of us in the northern hemisphere, except if you're indoors, where the problem is excessive dryness. That’s because our climate control systems counteract the cold mushy weather outside by cranking up the dry heat, which more often than not sucks moisture out of the air.

Dry air is bad for musical instruments. Anything made of wood usually likes to see a relative humidity index of between 45–55 percent. But forced air heat, without any other compensation, can drop the RH to 30 percent of even lower. That risks shrinkage in the wood parts of your instrument, which can cause glue joints to fail, the wood-to-wood-joined parts to separate, the finish to crack (called "checking"), and the frets to stick out of their slots on the fretboard. None of this is good for the guitar, nor the tone and tuning of the music coming from it. 

Here are the seven things to check for on your guitar to see if your guitar is suffering the effects of low humidity. This checklist was borrowed from Taylor Guitars' very helpful technical document on checking your instrument for dryness.

Dry Guitar Checkist

1. Low action. Strings are very close to the fretboard. With everything on your guitar shrinking because moisture is being sucked out of the wood, you'll often experience a change in playability. Everyone likes low action, but not at the expense of the wood contracting to the point that the strings are laying practically flat on the fingerboard. 

2. Hump on fretboard where neck joins body.Because the neck is more stable where it joins the body, you'll often see the neck area before it meets the body change, causing the most radical difference between the open part of the neck (from the headstock to the 14th fret). 

3. On Taylor NT necks, a slight gap around the fretboard extension. This applies only to Taylor guitars, but because of their NT construction, an additional checkpoint exists where the fingerboard extends beyond the neck mass. If there is any separation between the fingerboard extension itself and the rest of the neck, chances are a dryness condition contributed to this. 

4. Sunken top across the soundboard between the bridge and fingerboard. The area in front of the bridge (under the strings) is particularly vulnerable to change because no bracing is underneath to counteract any movement caused by shrinkage. If you see this area collapsed or sunken, in relation to the area behind the bridge and even further out to the sides of the narrowest part of the waist, you're experiencing wood contraction. 

5. Back of guitar looks very flat when it is dried out. The back of the guitar, under normal conditions, is not completely dead flat, but slightly bowed outward at the center. When the back of the guitar shrinks due to lack of proper humidity, the back "sucks in" to the braces, almost like a vacu-form process, and gives the appearance of being even flatter. 

6. Sharp fret ends extend beyond the edge of fretboard. When the fingerboard and the neck under it shrinks, the ends of the metal fret wires will stick out at the sides. There's also the possibility that the frets will get pushed up out of their slots, causing buzzing, action, and intonation problems as well. Often, you will feel the protruding metal fret ends on your fingers before you see them. Try running your left-hand thumb along the 6th-string side of the neck, and your fingertips along the 1st-string side of the neck, along the binding to see if you can detect any change in position between the side of the neck and the fretwire ends. 

7. The plane of the neck angle on a dry guitar hits above the top of the bridge. Use the edge of a yardstick or metal straightedge to help you determine if the "plane of the neck angle" (the slope of the neck as it progresses from the first fret to the saddle) falls below or above the top of the bridge. As a guitar shrinks from lack of proper moisture content in the wood, it doesn't do so uniformly. The shrinkage in the top, which is much less fixed, will be more dramatic. Consequently, the top will sink, and measuring the neck angle now reveals that a straight edge will end above the bridge, or with a gap between the straightedge and the top of the bridge.

MACHINE CONTROL

To prevent dryness mayhem, you must maintain a steady level of relative humidity in the environment where the guitars live. The best way to control the humidity is to employ a room humidifier and an inexpensive digital hygrometer, available from the local hardware store. These gadgets give the RH as a percentage (e.g., 50\\\%), and often do double-duty as thermometers. It's worth noting that as heat goes up, the RH goes down. In practical terms that means if you like the room on the warm side, you'll have to take extra steps to maintain the RH at the desired level. 

A room humidifier isn't that expensive, and if you can place the device in the room where both humans and instruments wil be, you can justify the expense for both. Often this means moving instruments into the living room for the times when the home-heating system is running at its highest.

LOW-TECH SOLUTIONS

If you can’t afford the appliance version of the humidifier, consider the low-tech sponge-type devices made by Planet Waves and Damp-It. These are essentially rubber-encased sponges that don't have any external monitoring or control. They just releases their water into the atmosphere through natural evaporation. But along with a hygrometer, you can achieve the proper balance just by moving the sponge around, and, if necessary, adding more of them to the mix. 

The biggest concern with a sponge is an obvious one: don't let it drip water inside your instrument or case. That means you must dunk the device in water, squeeze out the excess, and wipe dry before inserting inside the soundhole of a guitar. Throw your hygrometer into the case, and check often to make sure your reading are within the 45-55\\\% range. It's better to re-wet the sponge than to oversaturate and risk drippage. Often, you can use two, or even three (two in the soundhole, one up by the headstock), if you're in really dry and hot conditions. Keeping the guitar in its case helps to seal in the moisture generated by the sponges, so keep the lids closed (and at least on buckle engaged--more for security than as a sealing aid) whenever the guitar is not being played.

CONCLUSIONS

Whether you employ the more expensive AC-powered humidifier or go the sponge route, and outfit each case individually, you should take steps to ensure that your instruments are safe from the fluctuations of relative humidity due to the changing seasons. Keep in mind that by taking such RH-control measures, you're not just preserving the playability of your instrument and ensuring a buzz-free sound. You're actually reducing the stress on the instrument itself and prolonging its life.

Jon Chappell is a guitarist and Associate Editor at Harmony Central. He has contributed numerous musical pieces to film and TV, including Northern Exposure, Walker, Texas Ranger, All My Children,  and the feature film Bleeding Hearts, directed by actor-dancer Gregory Hines. He is the author of  The Recording Guitarist: A Guide for Home and Studio (Hal Leonard), Essential Scales & Modes (Backbeat Books), and Build Your Own PC Recording Studio (McGraw-Hill), and has written six books in the popular For Dummies series (Wiley Publishing).