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pakhan
01-22-2013, 04:00 PM
Dear friends,

I've been living in Singapore which is up to 30 Celsius, 90% relative humidity and even with a dry room, we've been running into issues with guitars until recently....

When I looked into relative humidity (RH) & absolute humidity (AH). It changed how I set up my dry room. Actually, I had looked into this when I was in London but had simply ignored it until now.

This info would be useful for anyone looking to care for their instruments, as the calculations can be worked either way for overly or under humid environments. I am using as a reference a conversion table issued by a German industrial site.

The main problem we all face is RH, but I believe that we should be looking at AH instead. Absolute humidity, is the actual amount of moisture in the air. IE, the amount of water vapor, usually discussed per unit volume.

Relative humidity on the otherhand is a %, ratio of the partial pressure of water vapor to the saturated vapor pressure of water. It is affected by pressure and temperature.

So even if we consider that the pressure is the same (it may not be), temperature alone is enough to throw things if we look at RH alone.

Say my uke is made in the USA. In a climate controlled environment of say 20 Celsius, 60% RH. This translates to an AH of 10.4 g/m3. (black circle)

It comes to me, at 30 Celsius, 90% RH. This translates to an AH of 27.3 g/m3. (black circle) This is almost 3x the original humidity. Even if I manage to get the RH down, to say 60%, the AH is still nearly double at 18.2 (yellow circle). This was the previous setup, and I was finding the guitars were still being affected.

In fact, to achieve an AH approximating 10.4, I should be looking at an RH of between 30-40% if I am at 30 Celsius. (green circle). The good news is that my dry room temperature is closer to 25 Celcius, so after switching to a target of 50%, I find things normalising.

The situation may be reversed in ukes, if you stay in a dry climate and the ukes were manufactured in a hot humid environment, say, vintage ukes in Hawaii. You would be looking at humidifying to close to 100% at 20 Celsius to even have a hope of matching 30 Celsius, 60% RH. Luckily old school luthiers were quite cunning and tried to perform critical tasks during periods of lower humidity.

Hope that helps and sheds a little light on humidity.

Incidentally, the pressure will also affect humidity, so the closer to sea level, the more humidity the air can hold and vice versa.


http://www.guitarbench.com/wp-content/uploads/2013/01/rg-diag.jpg

Dan Uke
01-22-2013, 04:03 PM
it's Greek to me

pakhan
01-22-2013, 04:38 PM
Lol, I can understand- basically even at the same % relative humidity, if you're at a higher temperature, the absolute humidity is higher.

SuzukHammer
01-22-2013, 09:37 PM
I understand it and thanks for the info. I have several ukuleles in Thailand and some in the desert and some in Colorado.

This graph will help me explain to the caretakers what I need from them.

THanks

drbekken
01-22-2013, 10:37 PM
Well, up here in the frozen arctic lands, all we worry about is to keep warm.

Barbablanca
01-22-2013, 11:16 PM
So what is an ideal humidity level then? I'm assuming it must be somewhere midway between tropical Africa and the Deserts of Siberia, is it? ;)

My studio, where most of my instruments are out of their cases and on display on stands, averages around 50% humidity (heating from a single radiator) and the winter temperature varies between about 16 at night and 20 when the heating is working (early morning and from sundown to 11pm). We are 360 metres above sea level and the general climate is Mediterranean. My most valuable instruments were either made in Mexico (Martin DX 1 AE) or wherever Kala and Ohana make their mid-range instruments (I'm guessing SE Asia).

So, given all that should I be happy or worried?

Trinimon
01-23-2013, 02:15 AM
I think I need someone to draw this out in crayon for me. :p

coolkayaker1
01-23-2013, 02:27 AM
So, let me see if I have this straight...

Oh, fiddlesticks. I don't.

HeWhoTalksLoudSayinNothin
01-23-2013, 05:36 AM
Well, overall its rather simple. What he is saying is that the humidity is also affected by the temperature you have. So 50% humidity at 10C is not the same as 50% humidity at 20C. Thus it might be that if the temperature where your instrument has been built in is very different from the temperature you have, it doesn't work that you only try to get the percentage humidity right, you have to adjust according to this chart, possibly even needing a higher percentage of humidity than you thought.

Plainsong
01-23-2013, 05:39 AM
Well most of us live in climate control, why not just keep the temp and RH constant?

Steedy
01-23-2013, 06:14 AM
Can we get this in a PowerPoint slide? ;)

Lalz
01-23-2013, 08:42 AM
What is the rationale behind using AH instead of RH? Doesn't the air's ability to hold moisture have more impact on how humid the wood gets?
100% RH in certain conditions can cause mould...

DaveVisi
01-23-2013, 09:57 AM
Well most of us live in climate control, why not just keep the temp and RH constant?

Bingo. Builders try to cover the bases by building to 50%RH and most likely a comfortable room temperature, let's say 72 degrees. That way you have the Sahara vs. Rain Forest range fairly well covered.

pakhan
01-23-2013, 10:16 AM
What is the rationale behind using AH instead of RH? Doesn't the air's ability to hold moisture have more impact on how humid the wood gets?
100% RH in certain conditions can cause mould...

The AH is a more accurate measure of how much humidity there is in the air as opposed to RH. As most folks don't take temperature and pressure into account when reading RH. SO simply using RH without temperature (and pressure) is like saying, this uke will cost 20% of a person's salary without stating the salary. As opposed to saying in AH, this uke costs $1000 which doesn't require further information.

pakhan
01-23-2013, 10:32 AM
So its -5F here in Colorado and about 10% RH, I should be ok....

I like to use the natural weight of the snow to glue my tops on ;)

Unless someone decides to store your ukes at 30 celcius, 90% RH........ with their own weight! :P

MutinousDoug
01-23-2013, 10:37 AM
I am not able to see how the weight of water vapor in a cubic meter of air translates to the availability of water vapor to escape or penetrate the wood of an instrument. RH tells me the availability of water to desiccate (10%) or saturate (90%) wood. Is H2O at 8grams/m3 at 10% RH going to affect wood the same way 8grams/m3 at 90% RH does?

Nicko
01-23-2013, 11:57 AM
I am not able to see how the weight of water vapor in a cubic meter of air translates to the availability of water vapor to escape or penetrate the wood of an instrument. RH tells me the availability of water to desiccate (10%) or saturate (90%) wood. Is H2O at 8grams/m3 at 10% RH going to affect wood the same way 8grams/m3 at 90% RH does?

That OXK formica is looking better and better all the time. :confused:

Moore Bettah Ukuleles
01-23-2013, 11:58 AM
I'm going out for a beer. Anyone wanna come?

Nicko
01-23-2013, 12:03 PM
I'm going out for a beer. Anyone wanna come?

:drool:
First round's on me.
:cheers:

bbycrts
01-23-2013, 01:02 PM
I am not able to see how the weight of water vapor in a cubic meter of air translates to the availability of water vapor to escape or penetrate the wood of an instrument. RH tells me the availability of water to desiccate (10%) or saturate (90%) wood. Is H2O at 8grams/m3 at 10% RH going to affect wood the same way 8grams/m3 at 90% RH does?

This was exactly where my brain went. It's not a matter of how much water is in the air, but how available that water is to affect the integrity of my uke, isn't it? A low relative humidity would indicate to me that the dryness of the air, for lack of a better term, would be tending to pull more moisture out of the objects around it, and with a wooden instrument that's not a good thing.

MutinousDoug
01-23-2013, 04:28 PM
bbycrts


This was exactly where my brain went. It's not a matter of how much water is in the air, but how available that water is to affect the integrity of my uke, isn't it? A low relative humidity would indicate to me that the dryness of the air, for lack of a better term, would be tending to pull more moisture out of the objects around it, and with a wooden instrument that's not a good thing.



I can theoretically see high humidity being as much a problem as low (although, at 5700 ft altitude and average RH at 20%, high RH is not a consideration here). I agree with the OP that observing the luthier's original atmospheric conditions should be ideal for preserving his works.
Builders used to use 12% RH kiln dried wood as a standard for home construction at least around here, in the desert.
Frankly, I'm afraid to consider a solid wood instrument even in my "music" room since my humidifier has been on all day, every day since November and the room rarely gets above 35% RH except at night. Occasionally, I even think about taking a vacation for a week or two. Without accompaniment.

Criminal, I know.

BlackBearUkes
01-23-2013, 05:11 PM
When I first got into luthiery, the question of moisture content in the wood and the Relative humidty were some of the first things I learned. Moisture content of the wood must be stable and in the 6% range. If you build in an environment where the RH is at a constant of 42-50%, measured on a high quality hygrometer, and the wood you are using is aged and at a constant 6% moisture percentage and the temperature is between 58-72 degrees, you should not have much trouble with your instruments even when they do experience sometimes drastic whether changes and humidity changes as long as those changes are not too lengthy. Right now in my part of the world, the day time outside temp has been about 22-30 degrees for a high and about 12-20 degrees for the low, and it has been this way for the last couple of weeks. When it gets this cold, the air is dry and the humidity gets sucked out of all the wood. The solution is to put it back into the air the water the wood needs so I can keep working. I am running one, sometimes two, cool mist humidifiers in my shop night and day to meet this need. My shop is well insulated and I have a excellent heat source so keeping things right is not difficult. Plan ahead.

No matter where you live, if you try to keep reasonable levels of RH and temperature (and I realize this can be extremely difficult), your instruments should be OK.

Plainsong
01-23-2013, 05:21 PM
I just got this new humidifier from a company called Ufox, which is popular in Finland. It's not as loud as previous humidifiers (emitting no noise) and it's not the cool steam kind. It seems to be a slow burner, but overnight the RH has risen from 70 degrees at 16% RH, to 70 degrees at 30% RH. I hope I can get it so that at least a few of the ukes can be on the wall, but even if I can't, my skin thanks me anyway.

I've spent lots of money in the past on those cool mist type humidifiers, since that was all the shops had, and the ones here generally last a year before they start sounding like motorboats. This one, seems to be doing well, we'll see. :)

SuzukHammer
01-23-2013, 06:00 PM
I live in a compound with set low utility rates - basically, my air conditioner/heating is free. I leave water sitting in pots all over the house and I keep a special closet with water pots for whenever I have to leave my house for a week or more.

I did notice at high heat and high humidity, I had a naked Fluke seem to get water (and salt) logged. I am close to a sea with high salt content so, I rarely will take out the uke because that salt doesn't seem to do any good.

What don't people talk about salt content in the air? Any luthiers have to deal with this?

Kamanaaloha
01-23-2013, 06:17 PM
Live in the same place where the ukes are built...or in a similar climate...problem solved! I guess moving to Phoenix or Pike's Peak is out of the question for me...otherwise crakety crack crack...or worse... submerge ukulele! <KIDDING>

Kamanaaloha
01-23-2013, 06:20 PM
I live in a compound with set low utility rates - basically, my air conditioner/heating is free. I leave water sitting in pots all over the house and I keep a special closet with water pots for whenever I have to leave my house for a week or more.

I did notice at high heat and high humidity, I had a naked Fluke seem to get water (and salt) logged. I am close to a sea with high salt content so, I rarely will take out the uke because that salt doesn't seem to do any good.

What don't people talk about salt content in the air? Any luthiers have to deal with this?

Any Luthiers make a fully dunked ukulele where inside and outside is coated? just curious...I am thinking so much for bright sounding...

Slingblab
02-24-2013, 06:32 AM
I just figured that my Kamaka Standard being such a fine instrument, it would bring it's own perfect humidity along with it here to it's new home in CA :D
Must be working. It's always 48 inside the hard case, which seems to run close with the RH in the room itself. Using a Herco inside the case brings it up to 56.

My Kala Concert inside of a gig bag has the same readings, while my acoustic 6 string comes in at 46 RH.

So is RH at 48 better than 56? Room temp is a fairly constant 68

Trying to determine if I even need to bother with using the Hercos.

quiltingshirley
02-24-2013, 06:41 AM
Okay that was interesting but hard. Since all our ukes were made in Hawaii (except the Dolphins) we'll just move to the islands. Much easier.