Acoustic guitar humidity is something you need to worry about. Constantly. At least that’s what many of today’s guitar manufacturers tell you. They actually try to plant this fear deep in your cortex. So that even a light summer shower will give you worries. And sleepless nights. But are these concerns well founded? We’re gonna find it out, bro.
Humidity in the old days
Last year, in our guitar string history article, we have checked a couple of old guitar catalogs. Catalogs from the early 1900s to the end of the WWII. They had practical suggestions on how to re-string your guitar, how to tune it, stuff like that. About the only advice regarding maintenance was to keep your acoustic guitar with the sound hole facing downwards. You know, just so the dust doesn’t get into it. They didn’t mention humidity though. Not even for those non steel string models. Now fast forward to today. Think about how many ads you have seen, how many forum posts and videos you have watched on the topic of guitar related humidity.
Does that mean that you shouldn’t worry about your acoustic instrument? Well, it means something like that. Those guitars are meant to be strong, when and if they are built and glued properly. Try to press down on the bridge and its surrounding area, when there are no strings on your steel string guitar. You’ll notice how little flexibility it has without the pulling forces of the strings. You are of course safer if you get a good, cheap hygrometer. Just so you can see the actual humidity changes your guitar can withstand without giving a crap about it.
How to make sure that the top of your guitar will not develop an extreme bulge suddenly? Set up your guitar to your likes (for the OCD people, preferably when it’s around the 45 – 50% RH level). Check the string action at the 12th fret. Note it down. If the humidity starts to raise, your action will do the same, gradually, in the following days. When your action reaches a point about 0.75 mm higher than your preferred action, throw some silica gel packages into your guitar case. I got this stuff out of the caps of fizzy vitamin tablets, and put it into a couple of fabric sacks. Now if the reverse thing happens to your acoustic guitar, and the action drops to a point about 0.5 – 0.75 mm below your initial setup, don’t worry. Anything that can hold some sponge or wet paper towel in your guitar case will work. I use a plastic cage of what was formerly a moth killer, with a piece of wet sponge inside. I hang it off the strings, right into the guitar, through the sound hole. Regular tap water will do. Once the action gets back to where you want it, you can stop using the sponge, until the action changes noticeably again. End of story.