Most guitars and ukes are constructed using seasoned wood and built in a controlled environment where humidity remains at a constant level of somewhere between 45% and 50% throughout the entire process. Builders do this to “lock in” all of the wooden parts of the instrument at an ideal geometry and moisture level. But even seasoned wood is hygroscopic and tends to dry out or swell depending on the level of moisture it loses or absorbs. This can have an adverse effect on your instrument.

A lot of players are aware of the major problems caused by an instrument drying out, such as cracks in the top, back or sides. There is also the possibility of fingerboard shrinkage, which usually results in frets protruding out the sides of the board, creating sharp edges that can tear up the player’s fingers. Ouch! Then of course there’s the lower action as the top shrinks, which can sometimes render the instrument unplayable due to excessive fret buzz.

Excessive moisture causes a whole different set of issues. Conditions such as bulging tops, backs and sides, warped necks, failed glue joints, separated bindings, mold, and finish checking are all too common. And as with dryout, there’s the change in the overall geometry of the instrument as the top domes, lifting the bridge higher, thus raising the action of the instrument, making it almost impossible to play.

In the end, both excessive dryness and moisture are equally destructive to your guitar or uke. All of these maladies can be avoided by employing humidity control both inside the case and the room where your instruments reside most of the time.

When Conditions Are Too Dry

Perhaps you own a number of guitars and/or ukes. Maybe they are scattered throughout your space, some hung on walls, some on stands, some in cases. Whatever the situation, the thought of having to maintain each instrument you own individually seems daunting. In situations like this, you might well consider a whole house humidifier. These can be very effective. However, the really good ones tend to be expensive and require some thought in terms of design and installation to ensure they properly humidify your space. For those of you who have all of your instruments concentrated in one room, as an alternative there are many great room humidifiers available ranging from under $100 to upwards of $1000 that will do a great job of keeping your space at the proper relative humidity (RH) level.

But let’s move on, as I really want to focus on the average guitar or uke owner of maybe one or two or a small handful of instruments. We need a simple means of protecting our ukes and guitars. This is where case humidifiers really shine. I use the term case humidifier quite broadly to cover any type of humidifier that resides inside your instrument case, whether it be in one of the negative spaces of the case itself or the soundhole of your guitar or uke. There are a lot of types of these around. I’m going to focus on a few to help you determine what might be best suited for you.

The simplest type of humidifier uses a sponge or other type of absorbent material to hold water which in turn disperses water vapor to moisturize your instrument. The absorbent material is moistened with water, or in some cases charged with a proprietary activation solution. Then it’s enclosed in a perforated rubber tube or a plastic container which is placed either inside your instrument or its case. These types of humidifiers are somewhat effective and have been around for years. In fact they are so simple, if you are industrious enough you can probably fashion your own. However, there are a number of drawbacks with them. First and foremost, they tend to dry out fairly quickly, sometimes within a day. You have to be vigilant in keeping the absorbent material moist for them to provide adequate protection. There is typically no refill indicator which makes it even more of a challenge to keep it properly saturated. As many folks seem to think more is better, there is always the risk of over-saturating these types of humidifiers which can lead to leaks and water damage.

A second and more reliable type of humidifier holds water in the form of a suspended gel in a porous but leak-proof reservoir. Water vapor is discharged through the container walls by means of osmosis. The potential for water damage is greatly reduced because there is no water to leak out as it has been converted to a thick gel which does not readily flow. There are several reasons why this type of humidifier is so attractive. First of all it is very effective for a longer period of time. Unlike the sponge-based products, it provides ample moisterization for as long as a week which means you are not going to have to potentially refill it daily. Secondly, the reservoir shrinks as it dries out, letting you know it is time for a refill. This type of humidifier also reduces the chances of damaging your instrument as it is made of very soft plastics which never come in contact with your instrument as it hangs in between the strings in the soundhole of your instrument or in a void of your case. Nonetheless, as attractive as these may be, in the end you still have to refill them with water at some point in time.

When Conditions Fluctuate Between Dry and Humid

A third type of humidifier is the two-way no-refill, essentially waterless humidifier. It uses a semi-permeable pack filled with a water and salt gum-like material that either releases or absorbs moisture, as needed. This system automatically maintains the optimal 45-50% RH level within your instrument case, eliminating the guesswork and potential mess related to refilling your humidifier with water. There is also no danger of water damage because no free flowing water is involved as the moisture is locked in the gum-like material in the enclosed packet. All you need to do is pop one in the soft mesh pouch that comes as part of the system. There is no need to be concerned with factors such as seasonal changes or temperature or geographic location, just let the laws of physics do their work. This is by far the most trouble-free and reliable means of protecting your instrument.

How Will You Know If It Works?

Let’s assume you’ve chosen a humidification system that suits your needs and budget. Your next step is coming up with some means of monitoring whether or not it’s doing its job. That’s where a hygrometer comes in handy. This device will enable you to measure the relative humidity in your case, or for that matter the room in which you store your guitar or uke. While there are some very fine mechanical hygrometers out there, like some very fine and expensive mechanical watches, they don’t keep time nearly as well as their thirty-dollar digital counterparts. You will do well by choosing a digital one instead as they are fairly inexpensive and in most cases more accurate and consistent than their mechanical counterparts.

While most hygrometers will read correctly to within a few percentage points, I have personally owned some that have been off by 10 or 15. With this is mind it makes a lot of sense to pick up a calibration kit to verify the accuracy of your hygrometer. These kits consist of a zipper bag and an enclosed packet containing water and salt gum-like material saturated to a specified relative humidity level, e.g., 75%. Place your hygrometer in the zipper bag along with the packet and seal the bag. Let it sit for 24-36 hours. Over that time the packet will equalize the atmosphere in the sealed bag to the RH level of 75%. Your hygrometer should read between 74.7% and 75.3%. If it doesn’t, it’s ok - just note the difference. This will be the number of percentage points you’ll need to add or subtract from the reading on your hygrometer to ensure accurate monitoring.

Armed with even this basic information you should be able to make a decision as to what type of protection you can provide your valuable instruments. As always, feel free to reach out to us if you have any questions or comments; we’ll be more than happy to respond.

Chuck Marfione, luthierWritten by:
Chuck Marfione
Luthier/Co-owner of All Strings Nylon