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Going to make several posts here and describe how I manage relative humidity in my home (and our commercial shop).

When new builders ask me what they should do to get started my reply is not one that is all that fun but it's important, very important to get this right before ever building a guitar.

An RH (relative humidity) solution is not negotiable in guitar building. Depending on your climate you must maintain around 42 - 48% RH or you will be building instruments that will react poorly to humidity changes. There are exceptions depending on climate. More specifically overly low action, sharp fret ends, fret buzz and rattle and cracks are all things that result from letting an instrument dry out.

I also put this on my Facebook page so I will be copy and pasting from there:

Managing The Humidity In Your Home For Guitar Folks

So once a year I get out the psycho-dyne and check my two primary hygrometers for accuracy and adjust them according if they are off.
I use old fashioned mechanical hygrometers which are the most accurate over time in my experience AND adjustable. The digital hygrometers are crap, period.

I've had builders push back on my declaration that the digitals are not any good because they recommend them.... We've tested them all including Caliber III and IV and same thing... crap.

Digital hygrometers use an electro chemical reaction to determine the relative humidity and over time the chemicals break down. I have three digitals in my home that are around 10 years old now and 13 - 18% off..... See, crap. They do tend to be close when new but over time, crap....

While all the while my two mechanical hygrometers continue to provide excellent service AND they are annually accurate in my experience within 1 - 2%.

This spring I wanted to check because it seems dry in the condo but I found that the hygrometers were still very accurate. The smaller one was 2% off and I believe it was 1% off last fall and that error was so small I did not adjust it out last fall.

The reason it is a little dry here is my furnace is not turning on as much because it's spring and my humidifier is a $900, 4,000 square foot commercial unit that I had installed here when I moved in. It's fully automatic, no more schlepping of H2O for Hesh here....

So here is a pictorial guide to how I maintain excellent humidity in my home for my guitars. Incidentally 45% which is the goal is also perfect for we humans. My tools never rust either at this RH percentage so lots of benefits.

I did correct the small hygrometer it was 2% off and the larger one was perfect and spot on.

Lastly when I pick up a guitar to play it the set-up is perfect and they never change here because the humidity does not change. A dry home can result in lifting bridges, sharp fret ends, lower action than you want, buzzing and fret rattle and.... if unaddressed over time "CRACK" as your acoustic instruments shrink but have no where to go. Now that I've warned folks twice.... maybe it will resonate.

I'll add comments to the individual pics for more detail if anyone is looking for same.

Here is my humidifier solution and it's been all that I would have hoped it to be.

Before this one I used to spend about $150 annually on humidifier wicks, chemicals and I had to schlepp water every day.... Now I replace the wick once a year, it's cheap and no water schlepping for me anymore.

I paid $900 for this system installed and it's starting it's 10th year now making it economical as well. My annual costs are one wick, $12, period!

Accuracy is excellent when the furnace is in play when it colder out the humidity stays a calibrated 45% +/- 1 - 2%.

This unit was made by Aprilaire and has worked flawlessly. It's plumbed into my hot water heater directly.

The control box measures the RH from the cold air intake of the furnace. If it drops below it's setting it turns on the hot water from the water heater and drips it over the humidifier wick. Excess water goes into the sump pump and is eventually pumped outside out the back of my condo. The humidified air is blown into all rooms in my home by the furnace. And it's all automatic and I don't have to touch it ever. I have my furnace checked annually and they always bring a new wick with them and I get an entire year out of one wick. Nice!

Here's why I appreciate an excellent RH solution that is fully automatic and very reliable.

Thanks for the gentle yet thorough reminder Hesh. I have a cheap April Air on the cold air intake and its $hit. It cant keep up most winters, and other winters I get condensate on my windows. It has poor control. I have no air ducts in my basement so I'm still shlepping. I am motivated however to get a sling hygrometer since [I] am the control mechanism.

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Measure Twice,

Karl Borum

The beginning of controlling humidity is controlling moisture infiltration. Concrete is essentially transparent to moisture: so basement workshops are a tough problem. Although there are waterproofing paints that claim to work well when applied to interior surfaces, they are said to fail regularly on things like basement walls owing to another property of concrete and mortar; low tensile strength. For reliable long-term performance, you have to put the waterproofing on the outside surface, and that's hard to do except in new construction.

My old basement workshop was a nightmare. Even when a heavy rain didn't send actual water into the shop there was no way to keep the R.H. down most of the year. When I moved into my current workshop I determined to do better. It's an existing barn, so there was no way I could waterproof the concrete floor from the outside. Instead I laid down a grid of pressure treated 2x4 2' by 4' OC. I filled in the spaces in between with closed cell foam, laid down a plastic vapor barrier, and then put down two layers of plywood for the floor, with the joints staggered. The walls and ceiling got a continuous vapor barrier before the sheet rock went on. I've had no problem since then keeping either the temperature or relative humidity in line. In the old days the two dehumidifiers would run so much that the shop would be up around 90 degrees much of the time, and the R.H. was still too high. Now I have no problem keeping the temperature around 72 with only one dehumidifier running and a min-split for A.C.

In the winter, when using the wood stove, I do have to run humidifiers, and keep a kettle of water on the stove. I found that one of the small stove-top fans that run off a thermoelectric Peltier junction does a good job of moving the vapor from the kettle around.

Note that many viruses degrade rapidly when the R.H. gets above about 40%; another good reason to keep it from getting too dry.

You're very welcome Karl I've had the inexpensive AprilAire units on furnaces before and they were as you say not very good and the wicks need frequent replacement.

My basement has fewer air ducts and no cold air intake so it's dependent on how the upstairs is maintained. But here where I live our basements tend to be more stable and higher RH in the winters anyway so it works out well for me.

I was not a believer in the unit I had installed until I used it the first season, wow, hand free, turn key, stable as can be. All good things.

Today is an example of when it does not work perfectly. The furnace has been off all day and it's dry out so I'm down around 42% on both calibrated hygrometers, one on each floor. But that's why we use a range and not a specific number to target, I'm still in range although at the edges.

In a few hours the temp will dip below the 73F (yeah I'm old and cold all the time...) that I set my heat to. Then it will come on, the hot water heater will be directed to wet the wick and in one running of the furnace I'll be at 46% again all over the place.

Good stuff Al especially the virus degrading info that's perhaps one of the most important reasons these days.

I used to joke here when I had my last home shop that I searched for and bought a house built in sand and I did do exactly that. Basement was around 45% all summer which is low for a Michigan basement. And I schlepped water all winter.

I should have also mentioned that no one is saying maintaining proper RH in a Lutherie shop is going to be easy and it's certainly not.

We are just finishing our first season with another solution that is at our commercial shop in the woods outside of Ann Arbor. It's ultra sonic but we don't get the white snow all over the place because it's fronted with a reverse osmosis unit complete with ozone to help keep it clean. It's all automatic, plumbed in so no schlepping either and it's been great all winter here. So far so good.

Jury is still out on how economical it is filter wise RO filters are expensive.

Yup. It’s amazing how fast the thin wood we use moves with RH swings.

I’ve been having troubles lately as my old reliable dehumidifier bit the dust and the new one isn’t doing its job very well.

It’s amazing to watch a back lose 1/16” of arc in just an hour or two of dropped humidity, or overswell with too much… happens fast!

I’ve been lucky in this department (considering I live in Ohio) in that my wood storage and humidity sensitive tasks (bracing, etc..) all happen in a small room that stays right at 45-48 almost all year. It’s in my basement with two exterior and two interior walls. I coated the floor with drilock paint and then put the drilock flooring squares down which makes an additional vapor barrier. LVP flooring is on top of the drilock. The ceiling is acoustic ceiling tiles. I have a dehumidifier in the room that is plumbed directly into the clear out cap for the plumbing going out to the street. It rarely kicks on.



I have an Abbeon hygrometer and calibrate it every year or so with potassium carbonate test.

I would like to do whole home humidity control like that, Hesh. Will look into it. Would be nice not to have to put all the guitars in cases from Dec to March.

Brad


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Yeah I can relate. I once decided to have a scotch and water on my back deck and sand the bottom of a top with braces before I attach it to the box. It potato chipped in 20 minutes outside of my shop..... Scared the hell out of me. I posted about it on the OLF back then.

The remedy was of course back in the shop, put it in the dish and weight it down for a couple of days and it returned. Whew....

Ed my dehumidifier does not work very well when it's still a bit chilly out so I could not turn mine on until maybe next month when the rains come and it gets warmer. Maybe you could trick the dehumidifier into working better if you turned up the heat. I think these things like a minimum of about 70F.

Very cool Brad some homes depending on where they are built are just drier than others, I had one of those too and my current condo is pretty good that way.

Having my entire condo at 45% year around is great for all concerned, the guitars and me and I have guitars in nearly every room here except the bathrooms and kitchen. I was not a believer in a furnace solution because of all the substandard ones out there/here but now nearly 10 years later with this rig it's been superb the entire time.

This time of year is a bit of a challenge because the RH can drop below 45% outside and it may be warm enough that the furnace does not kick on. But I still am seeing 42% and that is technically in range. This is the worse it ever gets here around 42%.

I should mention that I ran a dehumidifier in the unfinished part of the basement and that seems to keep the entire place under 50% all summer long. Like your's Brad mine drained into the house plumbing in my case the sump.

Excellent info as always Hesh!
Another whole-house option is the Aprilaire 800 Steam Humidifier.
Easily keeps my whole house at 44% per my Abbeon in the cold winters here in Alberta.
The canister only needs to be replaced once at the start of the cold season.
I have 2 canisters that I keep clean with a soak in cleaning vinegar after each season.

Hey Robbie you are very welcome and I hope that you are doing great these days!

We have a new solution in our shop that I forget the brand it's brand new and out of California. We love it and it has a RO unit and ozone too. We paid about $2K for it but in our biz stable RH is not optional.

The Aprilaire sounds great and it solves the snow problem in hard water areas of the ultrasonic units.

Great recommendation and even better results from you, very cool!

If you need a good humidifier/dehumidifier controller to replace the lousy ones on the units I have had one of these for years and it works well.

https://www.greenair.com/product-page/t ... ller-thc-2

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Thanks for this thread Hesh! I just won an auction for a NOS Taylor Sling Psychrometer on EBay for $17, SHIPPED. I was predicting the 330+ readers of this thread would cause a run on these on EBay! I’ve wanted one for years, we had one at work.

I purchased an Inkbird wireless set and it’s no better (one sensor really bad) than the other ones. I can choose the most accurate sensor now. Side by side the 4 sensors read 8 units of % off, worst case.

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Measure Twice,

Karl Borum

Question about applying a concrete sealer. If water can still enter concrete from below, but can’t exit because it’s sealed in, does that degrade the concrete over time?

In Al’s solution, does that scenario allow water to enter up through the concrete into the space below the subfloor, creating conditions for black mold?

Al is probably better to answer the question because his solution is fully sealed. I did not fill the expansion joints in my basement for reasons you're suggesting. Instead I made sure to have a high quality sump pump, backup pump and battery system to try to deal with the water vs completely blocking it out. The floor itself is sealed to deal with water evaporating from the surface, but the water could still push up through the expansion joints if the static pressure increased. So I just cross my fingers and check the battery backup status often.

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