Humidity Control and Your Guitar

May 13, 2019

Humidity Control and Your Guitar




Have you ever dropped an important piece of paper into a puddle of water? Did you fish it out, try to dry it off and straighten it out? Forgetting the damage it would do to the ink, you probably found that, no matter how great a job you did drying it out and flattening it under books, that piece of paper would never perfectly de-wrinkle or straighten out. Your important document is changed forever, it will NEVER be the same. This is exactly what happens to your guitar when it experiences drastic, prolonged humidity change.

This is a Vintage Gibson that lived in Arizona. It is exhibiting SERIOUS symptoms of over-dryness


With few exceptions, guitars are made of wood, a malleable and environmentally sensitive material. You’ve seen it before, when your back deck shrinks or the paneling on your house is water damaged. Wood reacts with the changes of moisture in the air, and it doesn’t have to be outside to do it! It is well known that a dry guitar is bad news, with acoustic instruments in particular experiencing top cracking and bridge splitting when things get too arid. When your guitar gets too dry, the wood starts to compress, which can lead to sunken tops, lower than comfortable string action, shrinking fretboards, and a hump in the fretboard over the neck joint. If left in this condition for long, the wood will literally crack like dirt under the sun. Inversely, a guitar that picks up too much moisture will begin to swell, which leads to swollen (or “bellied”) tops, high action, popped frets, and a waterlogged, dead sounding instrument. Likewise, if you leave a guitar in such tropical conditions for too long, you end up with failing glue joints and popped braces, along with finish issues and ruined neck angles. It’s difficult to say which is “worse” for your instrument, but it is widely held that a guitar can sustain too much moisture easier than it can too little. But in a place like Central Texas, where our humble shop resides, we get dramatic swings both ways depending on the season or any given day (or time of day for that matter!).

This dreadnought acoustic has some soundboard bellying that's causing the bridge to peel. Even a small amount of swelling like this can drastically inhibit sound and playability!

Many well-meaning and not-yet educated folks believe that having their guitar indoors with a decent air conditioner or heater is treatment enough for their instruments. And while the importance of temperature control cannot be understated, it is not sufficient humidity control for your precious acoustic instruments. The reason for this can be found in a concept called “Relative Humidity”, which deals with the interaction between moisture in the air and air temperature. Simply put, hot air can hold a lot more moisture than cold air can. This means that if you walked into your prized guitar showroom and saw that your thermometer read 50 degrees with humidity levels hovering around 60% or so, and you decided to quickly kick on the heater to dry it out, the room would lose a massive amount of moisture. Understanding this concept informs the astute guitar owner of an important lesson: temperature alone will not save your instruments from humidity damage.

Untreated room on the left, treated room on the right. It gets a little wet here in Texas!


So what can be done? Well, the first step is to arm yourself with knowledge and situational awareness. In short, you need to know which humidity level is optimal for your instruments, and you need to know exactly what the actual levels are in your showroom, studio, or case at all times. Conventional wisdom states that your guitar should remain between 40%-50% humidity at all times, with an air temperature around 74 degrees. You can track these levels with a hygrometer, which can be placed in your case or studio, with some models being WiFi capable, allowing for ‘round the clock monitoring! As always, knowing is half the battle, and remote meters will allow you to respond quickly to spikes and drops in humidity. Once your hygrometer is in place, the next step depends on your method of storage. The best place for your most sensitive instruments is in the case with a 2-way humidity system. These handy humidi-packs absorb moisture when levels are too high, and release it when things get dry, designed to maintain a certain percentage depending on which pack you buy. If you have your instruments out in the open, then you will need to treat the whole room, or building for that matter. This can be achieved with the use of room-level humidifiers and dehumidifiers. In our shop, we have a humidifier and dehumidifier constantly battling it out, keeping our guitars in that comfortable percentage year round. This method requires a good deal of maintenance, as your dehumidifier will pull staggering amounts of moisture out of the air (depending on your location) and need to be emptied regularly, and the humidifier will accumulate lots mineral residue if impure water is used. So if you are really concerned and looking for the quickest, easiest fix, you can’t go wrong with an in-case humidi-pack!

The back half of our vault, showing our dehumidifier in the foreground and the humidifier in the background

 If it’s too late and your guitar is already suffering, all is not lost, though repairs can be very expensive. If you notice your guitar getting too dry, the first step is to begin humidity treatment with a 2-way pack. You can also raise the saddle(s) and adjust the neck to compensate, but you’ll want to get it to optimum levels ASAP so it can relax. If the instrument begins to crack, it can be bagged with a couple humidi-packs and left to reacclimate for a couple months or so. After a while in the bag, the cracks will hopefully close up, and can then be sealed with glue and touched-up as needed. This whole process can quickly run you hundreds of dollars depending on the severity of the cracks. Likewise, if your instrument is too wet, you should begin treating it with a humidi-pack in the same way. In this case, the saddle(s) can be lowered and the neck can be adjusted to compensate for the swelling. If the instrument is severely over-wet, it may require neck resetting or bridge re-glueing if the top bellies. If the bellying is severe, it may require heat treatment to reduce the swelling. Again, these procedures can cost hundreds of dollars depending on severity, so it is best to implement preventative measures to avoid costly repair bills.

In closing, humidity is one of THE most important aspects of guitar care, and many other major issues can be prevented with proper humidity control. While temperature is doubtless a big player in this discussion, you have to pay special attention to humidity levels no matter what the season our temperature might be. Constant monitoring with a hygrometer, and implementation of proper humidity control measures is key to making your instruments last forever, and play great, too! Almost nothing is truly beyond repair, but repair rates can get pretty high if you’re not careful. If we could leave you with an analogy, it’d be to treat humidity control with the same import as you would the oil in your car; check it frequently and make changes when needed, or it could cost you your guitar.


If you’re interested in picking up some of the products mentioned here, check out the links below!

Boveda 2-Way Humidity Control  - Boveda makes the packs that DiAddario sells, so you can’t go wrong with either one. The 49% packs are the ones you should get!

DiAddario Humiditrack -This system works well, but it is a little pricey. It connects to your phone via Bluetooth, so you’ll have to be in range to get up-to-date readings.

AcuRite Indoor Thermometer and Hygrometer - This unit is VERY cost-effective and accurate. Get a few of them and spread them around your house!

AcuRite Home Environment Systems - This is the best option for monitoring your whole home. You can get add-ons and multiple sensors that cover every room in your house. And each one sends readings to an app or website.

Compressor Based Dehumidifier - There are lots of good brands (ours are Hisense), but you should look for a compressor based unit that will pull at least 50 pints per 24 hours.

Evaporative Humidifier - Again, there are plenty of sizes and good brands, but be sure to get an evaporative unit as it humidifies more evenly rather than spiking the moisture level.

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