How to Humidify Your Guitar
First published October 2012 - republished annually each October When I was young and innocent – young and stupid would be more accurate – back in the 60s, I carried a Martin D-28 all over Canada and down into California - in a cardboard case – hitchhiking, jumping trains and delivering drive-away dealer cars. The guitar not only survived my careless treatment but never suffered any ill effects from a lack of humidity. Truth be told no one seemed to be aware of any issues related to dry air back then.
Fifty years later it's different. Everyone is concerned about humidity – too much in hot summer or southern states and too little in dry winter conditions or high altitude climates. Why the change? ...more importantly..is there any reason for a guitarist to worry about the humidity?
To begin let's define humidity, or more accurately, relative humidity. The measurement of moisture in the air is always expressed as a percentage of the total moisture the air could hold – relative to the temperature. Listen to the weather report and you'll hear the announcer say something like “The relative humidity today is 40%” That doesn't mean 40% of the air is water vapour. It means that the air outside is holding 40% of the water vapour it is capable of holding. That's an important point to understand and gets us 1/2 way up humidity mountain. Its drier at the top which, of course, is the reason for the climb. To reach the summit we need to add in the temperature factor. Cold air holds less humidity than warm air but because we're measuring that vapour as a percentage of the air's ability to hold moisture it's not unusual to have a humidex reading of 40% or 50% or more in the height of winter. The air feels dry but has a humidity readout of 50%?
The same reading in summer produces insufferable dripping (dare I say it) sweat. Cold winter air simply can't hold much moisture so even a high (remember- relative to temperature) humidity reading is still pretty dry. 50% of not very much is still not very much. Here's where it becomes a train wreck for musicians, people, dogs, cats and pretty much everything except goldfish: Let's assume, for the sake of argument the humidity reading outside your window on a 0 Celsius (32 F) day is 40%. That's the air you're importing into your home. Question - Is it still going to have a relative humidity of 40% once you heat it to the 20-degree range (70F)? Absolutely not,
We're measuring the amount of moisture in the air relative to what it can hold and warm air can hold more moisture than cold air. Cold winter air, once heated to a comfortable temperature, can have a relative humidity of under 10%. Nature arbors a vacuum but she gets pissed off about discrepancies! The air in a building may have a very low humidity level but everything else in the building doesn't. That's a discrepancy in need of correction so moisture starts moving out of your skin, your furniture and (finally some relevance) your guitar into the air to achieve a balance. Your skin cracks, furniture joints dry out and guitar strings start buzzing. The balance, of course, is never achieved because we keep on sucking in new cold air, heating it up and lowering the interior humidity.
Buzzing strings and sharp fret ends are canaries in the coal mine for an acoustic owner - early warning signs of a need to humidify. The strings are likely buzzing because the top of the guitar has dried and dropped. Even 1/100th of an inch produces noticeable changes in playability. (NB. Altitude and atmospheric pressure can also cause a guitar top to move like a barometer). Fret ends are protruding because the neck is shrinking in girth as it sheds humidity. The guitar will be less playable – but more critically, continued exposure to dry air may result in permanent damage. Don't believe me? Take a look at every reputable guitar maker's warranty. Ask yourself why they all (we're no different) specifically exclude cracking due to lack of humidification. Wood shrinks across the grain as it drys. Constrained wood such as guitar tops with the bracing running perpendicular to the grain won't stop shrinking. It simply splits. What started life as a beautiful solid wood acoustic guitar can be reduced to kindling without a bit of care. So now we're solid on what relative humidity is all about and we're paranoid about protecting our guitars from its insatiable thirst. Good. Let's dump the theory lecture and put a working game plan in place.
If the environment where we keep our guitars is too dry the solution is to raise the humidity level. Not rocket science. But not brain dead simple either. The operative word in the above sentence is “IF”. Before we start pumping all kinds of moisture into the air we should know how much (if any) hydration we need. Over hydrating a guitar has its own set of problems. We also need to have a system that works for our specific needs. Establishing the actual relative humidity is accomplished with the use of simple (and cheap) little metering device called a hygrometer. Park it in a room and the needle or digital reading will pretty quickly tell you the relative humidity of that room. Once we know how dry the air is we'll use some sort of humidifier to raise the level to 40% or 50%. Here's the rub (or rubs). Rub 1 - No hygrometer I've ever seen is accurate. They can't be trusted. But they can be calibrated. Do a web search for calibrating a hygrometer with salt and you'll find a few dozen sites explaining how to establish your hygrometer's inaccuracy. Then add or subtract that amount to get an accurate reading. Rub 2 – Most methods of maintaining a decent moisture level suck the big one. Despite what that heating specialist (fast-talking salesman) told you, whole-house humidifiers attached to the furnace are useless. If you have one take your newly calibrated hygrometer on a tour of your house and watch the reading swing wildly from room to room. In-case, or soundhole humidifiers aren't ideal either. Some are better than others but they all rely on passive evaporation to draw out their moisture - not highly effective! They hold micro amounts of water that may or may not reach some parts of the guitar (one manufacturer specifically warns that their soundhole humidifier may do little or nothing for the neck. In very dry climates in-case humidifiers are, by themselves almost useless.
My personal preference is a stand-alone in-room humidifier. They don't cost a lot (most hardware and home decor stores run pretty good sales this time of year) and they do the job well. They have their own built-in hygrometer (no more accurate than the one you bought – you did buy one right? But at least you'll know and compensate for the error). Provided you keep your guitar in the same room as the humidifier (did I really need to make that point?) and you fill the humidifier when it runs dry (again, it seems obvious but...?) you'll go through the driest winter with a beautifully playable guitar. Some additional notes: A very good guitarist in Nova Scotia told me that he didn't need to humidify his guitars because he lived right beside the ocean. He was wrong (about humidity not about where he lived) The humidity level in his house in January was 22%. The physics of heating cold dry air doesn't change because you've got a lobster pond across the road. Another guitarist – this one in Alberta – had some musician friends over last October and handed one of them a guitar he'd stored away for a few months (no humidification) The guitar had cracked in storage. Some areas of the continent are drier than others. If you live just east of the Rockies the air you get is already dry at the best of times. Don't wait for the first snowfall - and don't rely on a tiny in-case humidifier. You'll destroy your guitar in a matter of (very cold) days.
Oh..and that Martin I campaigned across North America? Back then the construction techniques weren't as precise nor were the glues as binding as today. Wood may have been more seasoned (I have my doubts) and homes weren't very well insulated. Or perhaps I was just lucky on the road. I do know that somewhere near Salinas, ......