Most guitar owners are aware of the havoc that low humidity can cause but when it comes to high humidity, most of us are relatively clueless. I live in New England where the Winters are ridiculously cold and the Summers are hot and humid. The relative humidity in my shop in the Winter with the heat blasting can go as low as 10% and that will wreak havoc on any guitar. I keep a humidifier going 24/7 during the Winter that keeps the RH at 40% which seems to be just fine. But what about the really high humidity that is pretty common around here in the Summer?
Right now, it’s 78 degrees and the RH is 85%. That’s pretty nasty but by 10 PM tonight, according to weather.com, it’s going to be 70 degrees and 100%. What does that do to the “A” rack at OK Guitars? You know, the one with all the old 335’s, 345’s and 355’s. This week, it’s got five 59’s, a 60, 2 61’s, a 62, a 64 and a 65. Well, frankly, it doesn’t do much because I keep the A/C on and set at 74 which keeps the relative humidity around 50% on a humid day and 40% on a warm but dry(ish) day. No such thing as dry heat around here. According to the nice folks at Taylor Guitars, the optimum humidity for an acoustic guitar is 40 to 50%. Electric hollow bodies would follow the same rule and, while they are less reactive to humidity, solid and semi hollow guitars do well in that same environment. But there is another interesting factor to consider.
Back in the day, the wood used for guitars was air dried whereas today it is kiln dried. We are an impatient species and air drying simply takes too long, so we use heat to dry the wood before it is made into a guitar. Apparently (and I’m not an expert in wood), kiln dried wood is less stable that air dried wood so it would react more to changes in humidity. As it turns out, I have old guitars and new guitars in my shop and I can compare some of the effects of changes in humidity. Even though I try to keep the humidity stable, it still fluctuates 10 or 15% over the course of days and I do perceive some changes in some of the guitars. The newer guitars seem to be going out of tune-often sharp. I know the tuning pegs can’t turn themselves, so what is happening and why is it only the new ones? What’s happening is the wood is expanding-the same reason your doors won’t close in the Summer but close easily in the Winter. As the wood expands, the strings are drawn tighter and go sharp. And since kiln dried wood sucks up moisture more than old air dried wood, the newer guitars are more susceptible to expansion. It won’t turn your parlor guitar into a Dreadnought, but it will expand enough to affect the tone and the tuning. Wet wood doesn’t resonate as well as dry wood and some days, your guitar won’t sound as good as it does on others.
So, what do you do in the hot humid weather to keep your guitar in top form? Keeping it an an air conditioned space is a good start. I’m told that keeping it out of the case helps but there are some who disagree with this. If you have to take the guitar in the car, don’t put it in the trunk and don’t leave it in a hot car. That kind of heat can melt the glue joints. If you’re going a long way, keep the A/C humming and keep the direct sunlight off the case. Black Tolex will absorb a lot of heat. I drive a hatchback and it has one of those rollup shades, so I use that to keep the sun off. Or I put the guitar behind the front seat, so the A/C keeps it fairly cool. Finally, when you bring it indoors from a hot car and the case feels hot, don’t open it right away. Let it acclimate if you’re in a much cooler space. Your guitar will thank you.