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I started running a dehumidifier a couple of days ago in preparation for assembling my guitar, still a long way off but I wanted to see what the dehumidifier would do. The only hygrometer I have is the little one in my fiddle case so I put that on my bench and started watching. It stayed at 73% even though I've been emptying it regularly. This morning it was up to 78%! I'm thinking I may need to partition a small portion of the basement. This is a rented house so I don't want to go crazy with the walls. Any ideas?

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Hutch

Get the heck off the couch and go build a guitar!!!!

Let me first skip to the punch line: You might want to think about working with a drying cabinet for your guitar wood instead of trying to dry out the basement. Drying it out might be a big job that you won't want to tackle in a rented house.

More detail:

First, make sure you get a better hygrometer and a way to calibrate it for the range that matters to us. You need to work with more accurate data before you do anything. See other threads here on the OLF on ways to get more accurate readings.

Second, try to figure out where that much humidity is coming from. Where in the country do you live? If it is like where I live, that much humidity is just in the air for much of the year. But in a basement, you also need to be aware of sources of moisture other than what is just generally in the air in your part of the country. Is you basement fully below grade? Do you have a sump pump, or an interior French drain? There's just so much that can be happening in a basement to make it have a higher RH than you want.

Third, if you tried to section off the basement, you would need to really think through things like what the HVAC situation is down there, how you will get fresh air if you seal your workspace off, all of that. Then you get into really spending money, and since this is a rental house, you don't want to do that.

Fourth, think about whether the dehumidifier you have been using is really up to the task. An awful lot of the dehumidifiers you buy at big box stores are not very powerful. With RH as high as you have, you might need bigger guns. I use an Aprilaire stand-alone unit, and I am considering going with the kind that attaches directly to the HVAC system, because while the stand-alone does a great job, it works very hard.

In the end, you might be better off just drying out the wood, working with it for a few hours, then putting it in the drying cabinet when you are done. When you build the drying cabinet, be aware of fire safety please. You don't need to be starting a fire just to get dry guitar wood.

Good luck, and congrats for having the sense to worry about RH!

The larger dehumidifiers are more efficient than smaller ones, so even though they cost more at the start, energy savings will pay for difference. 72 pints is a good size, and it can;t be too big - that just means it runs less most of the time but is there if you need it. Any way to drain it into a sump or a sink? This avoids having to babysit the thing, and allows it to run more if you miss emptying it. The sump should be covered to prevent that same moisture from getting back in the air. Warming the air will reduce it's relatier humidity, so if it is cool down there in winter, a little heat helps - of course the dehumidifier adds a little heat.

Helps to check the outside perimeter of the house to see if there is a low spot that accumulates water during a rain. Good pitch to the ground? Gutters in good shape? You don't have to have visible water for the slab and block/concrete walls to pass a ton of moisture from outside and below.

Ed

Since you have a dehumidifier you could do a "drying closet" instead of a drying box. I build in an old rundown bungalow and only heat/cool the shop when I'm in there, and only one of the rooms at that. I use a small portable dehumidifier and place it in a plastic lined closet. The humidity is pretty well controlled in that closet and the machine doesn't have to work itself to death to do it. The closet allows me enough space for several projects and in the winter heating the room while I'm working in it lowers the R.H. enough to work all day without additional dehumidification. So between the closet dehumidifier when I'm not in the shop and heating the space when I am, things stay within a reasonable humidity level.
Also much of the work can be done in uncontrolled humidity conditions. It is only during some assembly operations where the R.H. is critical (and it truly is critical!)

Concrete is more or less 'transparent' to humidity. Running a dehumidifier in the basement is a great way to warm it up, but won't make it much dryer is there's any soil moisture and the walls were not waterproofed on the outside.

A drying cabinet will help, but you can't take stuff out for very long. A far better way is to make a 'tent' out of light lumber and sheet plastic, and dehumidify that. Get a storm door someplace with a closer, or, at least, rig something fairly tight, and don't forget to tape the joints in the plastic . It should be big enough for your work bench and go-bar deck if you have one, but the power tools can be out in the wet part of the basement.

So that you don't have to dredge up the thread from on calibration:

http://www.anzlf.com/viewtopic.php?t=6123

Here is the container I used with Potassium Carbonate:


Here is the Potassium Carbonate I used:
https://www.amazon.com/Potassium-Carbon ... dpSrc=srch

It's a hassle but worth knowing what you are actually reading is accurate.

I found that these cheap digitals were fairly accurate:
https://www.amazon.com/AcuRite-Accuracy ... dpSrc=srch

Use the OLF Amazon link to buy so Lance gets a few pennies.

Brad

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I also have a shop downstairs. I just use a single room. Stays a reasonable 40% w a de humid


Sent from my iPhone using Tapatalk Pro

Brad, the digital hygrometer/thermometer you linked to is on it's way to my door. Thanks

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

There are openings into little additions with dirt floors. I think it's hopeless without building a room. I'm pretty sure I'm going to have to get a piece of the spare bedroom for assembly and storage. We'll see how that goes

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

It only matters in closing the box right? How about when setting the neck?

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

I disagree with that. I think RH really starts to matter a lot, and never stops mattering that much, the moment you start gluing any braces to either the top or the back.

Real life problem (particularly in your wet environment): You glue the braces to the top when the RH is really high. Then, after you have built the guitar and are enjoying it, winter comes along. You heat your home, but don't humidify your home. In late January, you hear this loud CRACK! Yep, that was your soundboard.

This is why builders recommend building at around 40% RH. If the air gets really dry around a guitar that was built at 40% RH, cracks are less likely than if the guitar was built at 70% RH.

Remember that RH is "Relative" to the temp. If the amount of actual water vapor in the air stays the same and the temp drops, the RH goes up. That may explain the increase you saw. If you can isolate a corner with a heavy tarp on the floor and walls (cheap vinyl shower curtains will work also), and heat it up with the dehumidifier inside of it you may be able to drop it to a workable amount.

Once you begin assembly - putting things together - you should try to keep things in reasonable humidity.
You can "take a break" after the box is closed and before you fit the neck, but when you set the neck you need to bring the body back to the humidity it was assembled at (40-50% R.H.) and give it a day or so to stabilize.

Pretty hard to de-humidify dirt. Cover the dirt with tarp, something seal it and try again. Paint the concrete floors with sealant paint.
You must get control of your humidity (both dry and wet) if you want to successfully build instruments.
Every part of building instruments is affected by humidity control. Too wet is as bad as too dry. The answer is 42. %

I think once we get done with this ridiculous summer humidity here in RI, I might have a better shot at keeping the basement dry. I have a place for a bench in the spare room/guestroom but I'll have to be so careful with sawdust that it may not be any fun. One of those ceiling mounted things with the furnace filter may help. I'm really considering a closet in the basement but I'll wait until I try working in the spare room and see how it goes.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

When I bring in my workshop to the dining room table I set up 2, 20" box fans with high efficiency pleated HVAC filters duct taped to the "in" side of the fan. These are arranged at 45 deg to my chair blowing away from me and touch at the point. They're also on their side with the handle pointing towards me. I take a large piece of cardboard, duct tape it on top of the fans an make a roof over them...sort of a clean dust hood. This traps the majority of the small amount of hand sanding/sawing/scraping dust I create under it. Any machine work gets done in the cold shop. It's much easier to add humidity than remove it.

I like that idea Mark, that will come in handy.

I got my hygrometer last night and checked it against the one in my fiddle case. The new hygrometer measured 12% less. There are instructions for calibrating it but I guess you need a known good one to check it with or buy stuff, I can't remember the name and put it in a box. I'm just going to trust it as is.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

If you check Brad Combs' post from Monday the 17th, everything you need to know about how to calibrate a hygrometer for the range that is ideal for guitar builders is right there.

Basically, you get some potassium carbonate. It is readily available on eBay or Amazon; a small batch is less than $10. You put some in a small dish, then saturate it with distilled water. Then you put the dish and the hygrometer in a large Zip Lock bag or a plastic bin that seals well. Let it sit for a full 24 hours. The air inside the bag will absolutely have an RH of 43%. take the hygrometer out of the bag, quickly tweak it to 43%, and Bob's your uncle.

I would not trust any hygrometer without calibrating it. Think about it; you have two that were 12% off from each other. Maybe one is right and the other is wrong; maybe both are wrong. You don't know until you verify.

The reason you want potassium carbonate is that it is the specific salt that creates 43% RH when saturated. Other salts give different RH levels when saturated. You could just use table salt, but it creates a 75% RH level when saturated. That is really far off the range that matters to us. We want our environments to accurately hold an RH level in the 40-45% range, so we want our hygrometers to be accurate in that range.

I didn't pay enough attention to RH for my first several guitars, and I now regret that lack of attention. I take it pretty seriously now.

"There are instructions for calibrating it but I guess you need a known good one to check it with or buy stuff, I can't remember the name and put it in a box. I'm just going to trust it as is."

Read the instructions and follow them. That will atleast get you in the ball park. Some of them you calibrate by placing a moderately wet cloth over the sensor area for a set amount of time to mimic 100% humidity, and then set the indicator to 100%.

I was thinking about this last night while listening to the dehumidifier running in the basement. The average RH for Rhode Island is 61%. Why wouldn't I build to that? I would never have to worry about high action due to the top bulging. Even with the AC running during the summer, the RH doesn't go low enough to hurt the guitar. I may have to put a warning label in it stating if taken to drier climates keep humidified.

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

The reason that won’t work is because the winter is different. The reason winter is different is because, like the rest of us, you heat your home in the winter. When you do that, the RH in your home drops dramatically. The colder it gets outside, the more you heat your home, and the drier the air inside your home gets, compared to the air outside. See my post above regarding the CRACK you might hear.

New England is 'guitar hell' because of the swings in temperature and R.H. Back when I did repairs the crack season went from about February into April; it takes a while for the wood to really dry out, and then it takes it a while to catch up once the humidity starts to rise.

A guitar seems to be able to live in humidity about 20% lower than it was built in for some time, especially if it's had some time to acclimate. I build with the R.H. in the upper thirties to low forties so things should be good down to a sustained level of about 20%. I've seen 15% during cold snaps.

Keep in mind, too, that one of the things that happens to wood as it ages is 'shrinkage hysteresis'. As the wood goes through cycles of moisture it swells and shrinks with each change, but it never quite swells all the way back at the end of a complete cycle. This is probably due to the break down of hemicellulose over time, since that's the component of the structure that picks up and loses moisture. It's one reason we all prefer to build with older wood if we can; it's already shrunk. That may also be one advantage of Torrefaction.

What happens to a guitar built at 43%, "ideal RH", and the humidity goes through the roof for a few days or weeks as usually happens. Just high action or does it want to buckle?

I was at a local lutherie school recently listening to a jug band. I happened to notice a hygrometer on the wall. It read 23%!!

_________________
Hutch

Get the heck off the couch and go build a guitar!!!!

Usually, the guitar just swells up a bit here and there when the RH goes up. The worst thing a player normally experiences from the guitar being in too wet of an environment is that the action gets a bit high. In contrast, a guitar being in too dry of an environment has parts that start to shrink up. If you have ever felt sharp fret ends on the side of a neck, that is a common symptom of the air being to dry for that guitar. When it gets bad enough, the top can get a crack in it, as I have referenced a few times above. Without braces, your guitar's top would have the freedom to get as small as it needs to in order to react to the surrounding RH. But since there are cross-grain braces glued to the top, the top can't shrink as much as nature is wanting it to, so it cracks. It happens.

Don't confuse the weather report's RH level with what you have going on inside your home. When you take the outside air and heat it (as we all do in the winter), you lower the RH in the heated air. That's why humidifiers in winter are a good idea, whether that means the kind you stick in the soundhole, or have running in a room, or have hooked up to your HVAC system. Getting moisture back in the air around the guitar is important in the winter.

One advantage to the "X" bracing system as is typically used in Martin guitars. is that (aside from the upper transverse brace) the braces run at an angle to the soundboard, and the "cross grain gluing" is moderated by this. I believe this helps mitigate some of the effects of humidity swings. Of course the back bracing is strictly cross grain glued.