Humidity while gluing. (Full Version)

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r0bbie -> Humidity while gluing. (May 16 2007 12:36:45)


I want to start gluing the guitar but I wonder howlong before I have to lower the humidity. Can I start gluing as soon as the room is at 40% or do I need to keep the room 40% for a week or more and then start gluing?

Any help would be appreciated.

Sherman -> RE: Humidity while gluing. (May 17 2007 1:05:10)

It is my understanding that the longer you can let the wood age in the enviornment in which it will be built, the better. If the wood is used to being exposed to 60% humidity and you bring it into a 40% enviornment and start glueing it, I would expect problems. Likewise if the wood is used to 20% humidity and it is subjected to 40%, there will be problems. Perhaps this is why some luthiers build parts of a guitar, then set them aside for a few months. I don't know if there's any hard and fast rules though. Hope this helps.

jshelton5040 -> RE: Humidity while gluing. (May 17 2007 1:06:16)

Robbie, you don't provide enough information here. How are you controlling the humidity, with a dehumidifier? What exactly are you gluing? Most makers just keep their shop at 40-45% all the time. Wood needs a little time to acclimate to lower or higher humidity. If your wood has been in an uncontrolled environment you would be well advised to give it a little time to settle into the ideal humidity before working it.

John Shelton

r0bbie -> RE: Humidity while gluing. (May 17 2007 1:38:46)


I bought the wood from a suplier who kept the wood in a place where other people keep there car (garage?)
Then I left it in my house for a couple of months and I planed it to thickness, made the bracings and so on.

Normaly in holland we have plenty of rain but the last 40 days it has been dry and the humidity droped below 40%, then it started raining and inside my house the humidity went up to 56%.

I can controll the humidity with an airco but it makes a lot of noise and I drive my girlfriend nuts with playing the guitar allready so I dont dear to put her in the noise of the airco while she is sleeping [:)]

But there comes a day that I have to glue and it must be at the right humidity or the guitar might crack later on and that would be a shame. So, the wood had 40 days at +/- 40% and then the last 1,5 week rising to 56%.

I did not glue exept for the neck. Now almost all the wood is bent, planed to thickness and ready to glue but it has to be done in a short time span but when reading the post of John I think I just have to buy a dehumidifier and wait 1 or 2 weeks before gluing.

Well, when I am dead I wont need the money so why not buy a de-humidifier.....?


wiseguy493 -> RE: Humidity while gluing. (May 17 2007 2:16:16)

You should definitely buy a dehumidifier for the best results

You should also gauge the humidity and not just guess at it. I usually keep wood in a controlled environment for at least one month prior to glue. You may want to do that, unless you're quite sure that your approximations are very accurate

r0bbie -> RE: Humidity while gluing. (May 17 2007 11:42:06)

The first couple of weeks I had to guess because the controller I orded got lost and it took me a couple of months to get another. I assume that the controller is more accurate then the cheap hygrometers i've got and they have a difference of 20% (compared to the controller)

It seems that I have to get a de-humidifier that is silent and then wait some weeks before gluing.[:(]

Thanks for taking the time to answer!


Per Hallgren -> RE: Humidity while gluing. (May 17 2007 12:14:02)

There is always a big problem knowing what the relative humidity really is. I have four different hygrometers and the all show different values. Some are electronic and expensive, some are hair hygrometers of good quality. I regularly calibrate the hair hygrometers but not even then I get consistent values. I have made a wooden hygrometer from spruce that is easy to read and easy to make. The only problem when making it is to know if your humidity is correct or not.

r0bbie -> RE: Humidity while gluing. (May 17 2007 13:16:03)

Can you tell me more about the wooden hygrometer? How good is it and can I make one?


The only problem when making it is to know if your humidity is correct or not.

Do you meen it is difficult to callibrate the hygrometer?

I tried to make one myself and I sneaked in one of the boxes for the horses and yanked out a hair of the tail and run away. But it was not very accurate so I never used it.


Per Hallgren -> RE: Humidity while gluing. (May 17 2007 14:39:36)

No, to calibrate is easy. Just put a wet towell around the hygrometer for an hour and set the value to 100%. The problem is that the hygrometers show different values even if the are newly calibrated and sitting on the same spot in the same room. So which one is to trust?

My wooden hygrometer is very reliable if I only knew which value it was made in (i.e. which hygrometer to trust for a true value). It is made of crossgrain spruce laminated with spruce with the grain lengthwise. The crossgrain spruce is a couple of millimeters while the other is only a couple of tenths of a millimeter. When the crossgrain spruce try to expand or contract because of changed humidity the lengthwise spruce makes it to bend instead. If this spruce stick is straight I know that the humidity is the same as when the stick was made (whatever that was...).

GregF -> RE: Humidity while gluing. (May 17 2007 15:31:10)

To calibrate your hygrometer you should make or buy a sling psychrometer. This is the standard instrument for measuring relative humidity. They are very easy to make. Check this web site for more information on how it works and how to build one.


Per Hallgren -> RE: Humidity while gluing. (May 17 2007 16:51:59)

Yes, I know. I just explained a "cheap and dirty" way to calibrate. Maybe I should have been more accurate...

r0bbie -> RE: Humidity while gluing. (May 17 2007 23:04:22)

I had heard before that you could measure with thermometers but I did not know how. Now I do :-)

But how accurate is it? and does it matter how fast you sling it around?
I would say that the faster you turn it around the more it cools down, just as the cooling effect of wind when it freezes.

Maybe I'll try this, just for fun. I have to secure the thermometers because I dont want to launch a missile near the guitar wood[&:]

GregF -> RE: Humidity while gluing. (May 18 2007 22:05:21)

This is pretty much the standard method for determining relative humidity. It is as accurate as your thermometers. It is true that the faster you sling it around, the faster the wet bulb will cool down, but when it reaches equilibrium, the temperature will stop dropping. Then you take your temperature readings and look up the humidity.


r0bbie -> RE: Humidity while gluing. (May 19 2007 0:45:59)

I can calibrate the thermometers so I am defenite gonna try this to see if the electronic humidity meter is accurate or not.


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