I hear that the relative humidity of your shop is very important for building guitars and should be between 40 and 50%.

I think I can maintain that in my house pretty much year round, but my shop is my garage. Now that fall is here it is getting a little damper and the humidity in my garage is getting up to close to 70% at times. I have been storing my wood inside the house when I'm not working on it, but it is getting less convenient to bring the guitar assembly in and out.

What is the best way to lower the relative humidity? I'm guessing the only way is to heat the garage and vent it with a fan. How big a fan do I need?


Doug Collins

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I'd use a dehumidifier to bring the humidity down when heat is not needed. During the heating season, heating will bring the humidity down, even to the point where you may have to humidify to keep above 30% humidity.

Being that I live in an area that humid conditions never really occur (at least from a comfort point of view) the thought of a dehumidifier never even crossed my mind. I wonder if I can even buy one locally? I can't imagine why anyone would buy one for any other reason.

So, even though it's not quite heating season right now, will heating the garage lower the relative humidity right now. The garage is cool enough that if wouldn't necessarily get hot in there.


Yes, without doing anything else, heating the space will lower the RH, because warm air has the potential to hold more water.

Heating your workspace will also extend the working time of hide glue, by the way.

Keep in mind that a CHANGE in RH will affect the wood more than the actual humidity. You mentioned you "store the wood in the house when you're not working on it".

So for example, if you took a neck and body acclimated to your house to your garage and glued the neck, then brought it back inside(or left it in the garage), you would potentially be compromising the integrity of the glued joint.

It's a lot like installing hardwood floors, where manufacturers recommend acclimating the wood to the installation environment for a certain period of time BEFORE installing it. If really dry wood is installed in a humid environment it will swell up perpendicular to the grain, creating an arch between the boards.

Conversely, if wood with a higher moister content is installed in a dry environment, it will shrink and leave gaps between the boards.

40~50% is recommended because it is middle of the road for all types of environments the instrument would expect to see in its lifetime.

Assuming your garage has a concrete floor, you might consider sealing it. Also make sure you have good drainage from your gutters well away from your structure.

I do my building in my basement, I keep a dehumidifier on standby, as I get a spike in humidity after a heavy rain. They're not that expensive, and come with a humidity setpoint.
I read somewhere that bringing the wood back inside was a good idea if you don't have control of the humidity in the garage. I wondered if this change in environments would not be harmful, as you say. However, with the relative humidity in my garage a 70%, the glue will take forever to dry.

If I'm just taking the wood into the garage for short periods of time to cut and glue (maybe 15 minutes), do you think this is long enough to adversely affect the wood?


I think you'd be better off storing your wood in the same environment that you do your building in. It would eliminate the swings in relative humidity that can raise havoc with wood. Unless you're buying large amounts of wood at a time, most lutherie woods don't take up that much space. I build in my basement and I store my woods in a climate controlled enclosure I built myself that is about 3'x4'x6' high, which is actually bigger than I really need. Here in the upper Midwest, we get summertime RH's of 70-80% at times, and during the winter, when we're heating non-stop, the indoor RH's can drop below 20%. I find that I have high humidity most of the year and I controll the RH in my wood storage container by adding heat in the form of 1 or 2 low-wattage light bulbs near the bottom of the container. I also try to controll RH in my shop by running a dehumidifier pretty much all summer, supplimented with my whole-house central AC when things get too hot/humid. I've had to do a whole gamut of things to try and keep RH as low as I can in the summer by a) air-sealing the sill-foundation joint of the house, b) using waterproofing paint on the interior foundation walls, c)using EPS (extruded polystyrene) foam insulation on the foundation interior walls, and d) installing an epoxy floor coating. Even with all that, the RH in the shop can still edge up into the 60% range. When it gets that high I stop trying to glue things together and just wait until it drops into the low 50% range or lower. I know other luthiers who build like mad all winter and do all their finishing work in the summer. I believe it's better to do the building at the low end of the RH range, as it seems less damaging to the joints to let things swell, than it is to let them dry out too much. During the winter, when RH's get too low, I just run a small humidifier in the shop, which also helps keep the RH in the rest of my house at more reasonable levels too.
When I first got interested in lutherie about 10 years ago, Luthier's Merchantile (LMI) put out a catalog/handbook that had a very good discussion about the various levels of humidity of interest to luthiers and methods of measuring and controlling it. I don't know if they still offer this or not. Also, the GAL has lots of info in back issues of their excellent publications. Hope some of this helps.


Simply moved into our home in mid-April however have discovered molds on a lot of things being kept in the garage, especially developing on texture on the infant baby buggies, my golf travel bag, and so forth.

I'm not a mold remediation master, yet I figure the presence of mind things would be air movement and dehumidification. Dehumidifying will be an errand except if your garage is insulated. Air movement with a fan or two should support a few (perhaps). With you having a built-up issue I would, in any event, set up two on either side of the garage and blowing in inverse ways to frame a vortex.

You can likewise get a dehumidifier (as enormous as you can find...usually 70 pints for every day in most improvement stores...over 70 pints and they take a sensational bounce in price...). Turn it on high or set it to 40% humidity and let it roll.

  • You should utilize the hose channel connection, however, that is effectively practiced by running the hose through a vent in your garage wall. Else, it will just run a couple of hours before the reservoir is full and the unit consequently closes down.

I explored for my dehumidifier and arrived on a website page I cross-checked its substance and discovered relevant data in it.

Before I moved I had an enormous extra space that was uninsulated. I mounted a 50-half quart unit on a rack over a utility sink. I steered the channel hose down into the sink. Kept that room pleasant and dry...noticeably not quite the same as the outside moistness.

NOTE: You can use a bleach/water mix to get rid of the mold you have present. You can also use rubbing alcohol. Spray either in a bottle or if you have A LOT to deal with just use a garden pump sprayer.

Good luck.


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