Wherever you live and whatever the climate, don’t forget to keep your humidity levels in check. Your guitars will thank you!
For guitarists, things get a little crazy twice each year. I’m not talking about the NAMM convention—it’s bigger than that. Both summer and winter bring temperature and humidity extremes to bear on wooden instruments, and if you’re not prepared, things can get ugly. Dry air shrinks wood and splits guitar parts. Humid air swells tops and fretboards, wreaking havoc on setups and finishes. It’s important to know that damage caused by failure to anticipate this natural occurrence is not a defect in the instrument. Many times, trips to the repair shop can be avoided by simple climate control.
It’s a full-time job for guitar builders, but what we do to cope with nature’s swings has lessons for guitar owners as well. Modern indoor climate control means most people live and work in a fairly narrow range of temperatures, regardless of where they reside. We all know not to leave a guitar in the car trunk when temperatures soar or plummet, but inside of your home, the culprit is humidity.
The yearly average humidity in North America (and around the world) provides an incredibly wide range of numbers. Nevada’s 38.30 percent yearly average is a world apart from Alaska’s surprising 77.10 percent, and that’s just the average. But even these numbers don’t tell the whole story. When you factor in temperature, things can get better, or they can get much worse. What we’re interested in is relative humidity (RH), which is the percentage of water vapor in the air at a given temperature.
Different regions require different approaches. Both Arizona and Louisiana can be crazy hot in the summer, but their humidity levels couldn’t be more different. In the Southwest, air conditioning that’s working overtime to cool is also stripping moisture from the air. Whereas in New Orleans, getting things dried out is a constant battle. It’s safe to say that most places need both temperature and humidity control to avoid problems.
Many times, trips to the repair shop can be avoided by simple climate control.
Manufacturers can’t afford the damage that humidity (or lack of it) can bring. When RH drops too quickly, expensive stockpiles of tonewoods can crack, reducing them to firewood. At the very least, swings in humidity can make wooden parts hard to fit, especially when they’re machined to tight tolerances by CNC. In a guitarist’s home, low humidity can split tops and shrink bodies resulting in delamination of bindings or bridges. Fretboards not protected with finish are the first things to react to changing humidity, bowing or warping enough to render an instrument unplayable. High humidity expands the fretboard, forcing the neck into a backwards bow, whereas low humidity shrinkage creates an opposite, forward bow. Shrinking fretboards also reveal fret ends which can be uncomfortable at best. In some cases, expansion and shrinking may cause finish to flake off, especially at sharp corners or fretboard edges. Needless to say, this isn’t what you want happening to your collection.
The good news is that if you keep most of your instruments in a single room, it won’t be too hard to control the humidity. The first step is to get an accurate hygrometer to determine what the current RH is in your space. Most times, the problem is low humidity. In that case, calculate the room size and begin your search for a room humidifier to match your needs. If humidity is high, you’ll need a dehumidifier, and you can use the same method to determine the size. Keep the RH between 35 and 45 percent to be safe. Your room needs to be sealed off. Otherwise your efforts will literally go out the window. I like the type of unit that senses the humidity, and you can just set it and forget it—until it’s time to fill (or empty) the tank. The trick is not to have them both on at once. They’ll just get into a never-ending battle with each other. You’ll have to monitor things to know when to switch over as the seasons change.
At home or in a small studio, you can control your instrument’s environment for a relatively small outlay. A few hundred bucks is way more affordable than crack repairs. It also keeps things comfy, which is a nice bonus. Think of it as a large pedal whose effect is keeping your guitars playing right and protecting your investment.
Have you ever wondered why your guitar plays great one day, yet feels completely different on another?
Have you ever wondered why your guitar plays great one day, yet feels completely different on another? Suddenly the fret edges are sharp or the action has shifted and the guitar won’t play in tune anymore. These changes can happen overnight, especially in the winter. Cold, dry weather brings low humidity and that causes cracked guitars. Winter is my busiest time of year for structural repairs, and most of these repairs are preventable with an inexpensive humidifier. I’ve been preaching this message for more than two decades: Preventive measures are the key to keeping your guitar in top condition.
Dealing with humidity.
Humidity is the amount of moisture or water vapor in the air. The more moisture in the air, the higher the humidity. Lesser amounts of moisture results in lower humidity.
There’s a popular myth that a guitar sounds better when it dries out. Actually, it just cracks and then I get to charge a fortune to repair it. This myth is often confused with a guitar’s natural aging process. When a guitar ages, cells in its wood begin to crystallize and harden, causing the guitar to get louder and more dynamic. But if it’s not properly humidified, the wood will crack. (Did I mention structural repairs are very expensive?)
But you can have too much of a good thing: When a guitar is over humidified, it swells up and loses volume and tone. (Think of a tub of lard with strings.) High humidity can also cause finish discoloration and even allow mold to grow inside the guitar.
The way to avoid these problems is to maintain a consistent humidity level for your instrument—particularly an acoustic hollowbody. This will prevent a host of ailments and costly repairs.
Symptoms of low humidity.
One of the common telltale signs of a dry guitar is sharp fret ends. When a guitar dries out, the fretboard shrinks and the frets protrude beyond the wood. Correcting this problem requires re-humidification, conditioning, and fret filing. If your guitar is showing signs of low humidity (sharp fret ends, cracks, or separated glue joints), you need to have it evaluated by a reputable luthier.
This is what happens to a dry guitar in various levels of low humidity.
LEFT: Fig. 1. This top cracked from lack of humidity. MIDDLE: Fig. 2. Fretboards can also crack as a result of low humidity. RIGHT: Fig. 3. The Humidipak guitar humidifier system.
Photo courtesy of Planet Waves
Below 35 percent humidity:
- Action (string height) changes.
- The top flattens out.
- Fret ends feel a little sharp.
Below 25 percent humidity:
- Fret ends become very sharp.
- There are drastic changes in the playability.
- Seams begin to separate.
- There’s a slight separation between the bridge and top.
- The finish starts to sink.
Below 15 percent humidity:
- Cracks appear in the top and body (Fig. 1).
- The bridge and fretboard crack (Fig. 2).
- The glue joints in the neck, bridge, and braces begin to separate.
What is the best humidity level for my guitar?
Most experts say 40-50 percent. At this level, a guitar will sound and play its best. A great way to control humidity is to use a humidifier. Think of it as an inexpensive insurance policy to protect you from very expensive repairs.
A guitar humidifier is easy to use and very effective. Some guitar humidifiers are suspended between the 3rd and 4th strings and contain a damp sponge that needs remoistened every two or three days. This type of product works okay, but it’s not consistent. The humidity will spike at first, then slowly diminish as the sponge dries out.
The more modern guitar humidifiers use a gel that not only emits humidity, but also absorbs it if the humidity gets too high. This technology was first developed for cigar humidors, and now it’s available for guitars. Planet Waves makes a great humidity control system called the Humidipak that uses this technology (Fig. 3.). I’d also recommend using a hygrometer to measure the humidity.
LEFT: Fig. 4. A room humidifier in action. MIDDLE: Fig. 5. Thanks to heat exposure, this bridge separated from the top leaving a gap big enough to slide in a seam separation knife blade. RIGHT: Fig. 6. Use a wood conditioner to protect your rosewood or ebony fretboard.
Another great way to control humidity is to use a room humidifier. This is a great idea if you have multiple guitars in one room. Humidifiers come in all shapes and sizes, but be very selective, as some work much better than others. I use a programmable humidifier that utilizes both “warm mist” and “ultrasonic technology.” It also has a built-in hygrometer and a UV light to help purify the water. This type of humidifier is much healthier than the “cool mist” types that require a filter.
What guitars need to be humidified?
All guitars should be humidified, even electric solidbodies. Newer guitars generally need more moisture because the wood is kiln-dried, as opposed to a vintage guitar made from air-dried wood. The difference between kiln and air-dried wood is dramatic. Kiln-dried wood uses heat to dry the wood to accelerate the aging process. However, these guitars require more moisture to prevent warping and cracking. Air-dried wood is more stable, especially in vintage guitars, because the wood was generally aged over a decade before being made into a guitar. As a result, the cracked wood was removed from the pile and used for something else. Guitars made from air-dried wood still need humidity to sound best, but they retain moisture better than their modern counterparts.
Too hot to handle!
Heat exposure can also have destructive effects on a guitar. When a guitar is left in the trunk of a car—especially on a sunny day—the glue joints can fail. Imagine the shock of opening your case and finding a pile of wood where your guitar used to be. Once again, I get to charge a fortune for repairing heat-damaged guitars, so be vigilant.
A frigid nightmare.
Cold is also an enemy. When a guitar is exposed to low temperatures and then brought into a warm environment, the finish can develop checking. Checking creates tiny hairline cracks in the finish—like someone laid a spider web over the finish— and you can’t polish this out. Finish checking is permanent and can only be repaired by refinishing (not something I would recommend). Finish checking is basically the result of the finish changing from one temperature extreme to the other. This causes the finish to expand and contract too fast, and that makes it crack. To minimize this, when you bring your guitar in from the cold, don’t open the case until the outside of the case is at room temperature. Even then, there’s no guarantee the finish won’t check, but it will lessen the odds.
Okay, let’s review—here’s how to prevent damage to your beloved guitar:
- Buy a guitar humidifier.
- Keep your guitar at between 40–50 percent humidity.
- Use a hygrometer.
- Keep your guitar in a consistent environment (one that’s comfortable for you).
- Keep it out of direct sunlight and out of the car trunk.
These simple steps can save you hundreds of dollars in repairs.
[Updated 12/30/21]