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Moisture Content Question
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=34911		 Page 1 of 1
Author:  Dave Livermore [ Tue Jan 10, 2012 7:15 pm ]
Post subject:  Moisture Content Question
Just got the shop climate figured out and things are FINALLY stabilized.

Also bought a moisture content meter.


Humidity was REALLY high for a long time and now is hanging around 50%.

What readings should I be getting on my wood stash.

Right now all the tops in the stash are b/w 12 and 14% and the hardwood reads b/w 6%-9%.

Not ever taking readings before I don't know if these are normal, or high or low for wood that's been in the shop for over a year.

Thoughts?

Thanks,

Dave
Author:  Jeff Highland [ Tue Jan 10, 2012 7:25 pm ]
Post subject:  Re: Moisture Content Question
As far as I know Moisture content meters do not give accurate readings on thin timber, which is why everone just lets it stabilize at a target RH
I would expect ready to build with timbers to be around 8%
Author:  Alex Kleon [ Tue Jan 10, 2012 8:36 pm ]
Post subject:  Re: Moisture Content Question
Dave , did your moisture meter come with a species and temperature correction chart? For many woods, the reading on your meter must be re-calculated based on species. The industry standard species is Douglas Fir, measured at 68*Fahrenheit. Some woods that measure say 10% will have a corrected MC of 13%, while others may be as low as 8%. At lower readings the correction isn't that much, but the temperature of the wood will affect the true MC reading, and that must be calculated as well. I found a table that might help.http://www.comproteccanada.com/species.htm There are others that may show more species, and temp. correction tables. One thing that you can do is chart the moisture in a couple of pieces of wood on a daily basis for 14-28 days. You will likely see the readings go up and down for a while, and then remain pretty much the same, but the temperature must remain constant or the readings will not be accurate.

Alex
Author:  Dave Livermore [ Tue Jan 10, 2012 9:08 pm ]
Post subject:  Re: Moisture Content Question
Thanks Alex.
I should have figured it would be complicated like that.

Will check out the link.

Dave
Author:  John Arnold [ Wed Jan 11, 2012 1:38 am ]
Post subject:  Re: Moisture Content Question
This is the equilibrium moisture content chart that I use. I forget its source.
Temperature = 70 degrees F.
RH......EMC in wood
20......4.5
25......5.4
30......6.2
35......6.9
40......7.7
45......8.5
50......9.2
55......10.0
60......11.0
65......12.0
70......13.1
75......14.4
80......16.0
Quote:
As far as I know Moisture content meters do not give accurate readings on thin timber,

I have always heard that, but I seem to get pretty consistent readings from the thin wood I have tested. Even so, the best test to check for equilibrium of thin wood is simple, and requires no moisture meter.
Just lay the wood flat with one side exposed. If the wood curls, it is not in equilibrium. If the exposed side becomes concave, the wood is losing moisture to the surrounding air. If it becomes convex, it is gaining moisture. Flipping the wood over will cause the curvature to reverse. Repeat the process until the wood stops curling....then it is in equilibrium.
Author:  Alex Kleon [ Wed Jan 11, 2012 3:26 pm ]
Post subject:  Re: Moisture Content Question
John Arnold wrote:
I have always heard that, but I seem to get pretty consistent readings from the thin wood I have tested. Even so, the best test to check for equilibrium of thin wood is simple, and requires no moisture meter.
Just lay the wood flat with one side exposed. If the wood curls, it is not in equilibrium. If the exposed side becomes concave, the wood is losing moisture to the surrounding air. If it becomes convex, it is gaining moisture. Flipping the wood over will cause the curvature to reverse. Repeat the process until the wood stops curling....then it is in equilibrium.
John, I am assuming this applies pretty much only to quarter sawn wood? I've never had a piece of cupped flat sawn wood correct itself by the flip method, and I have tried. [headinwall]

Alex
Author:  B. Howard [ Wed Jan 11, 2012 8:38 pm ]
Post subject:  Re: Moisture Content Question
I weigh mine. When the weight stabilizes, they are at a stable EMC relative to the environment. So as long as your shop climate is proper and stable they are ready to go at that point.
Author:  Peter Tsiorba [ Sun Jan 15, 2012 11:48 pm ]
Post subject:  Re: Moisture Content Question
I second weighing as a reliable indicator of stabilized RH. Gram scale, accurate down to .1g can be had on ebay for under $25. It can be useful for all sorts of other research/application around the shop.
Author:  John Arnold [ Mon Jan 16, 2012 5:50 pm ]
Post subject:  Re: Moisture Content Question
Quote:
John, I am assuming this applies pretty much only to quarter sawn wood?

It applies to all wood. The reason for the cupping is uneven moisture distribution.
Quote:
I've never had a piece of cupped flat sawn wood correct itself by the flip method, and I have tried.

That is because it has moved enough to take a permanent set. That only happens during the initial seasoning....when the wood is dried from a green state. In my experience, once the MC reaches 12-14%, it responds as I explained, no matter how it was cut.
Author:  Corky Long [ Wed Jan 18, 2012 11:49 am ]
Post subject:  Re: Moisture Content Question
B. Howard wrote:
I weigh mine. When the weight stabilizes, they are at a stable EMC relative to the environment. So as long as your shop climate is proper and stable they are ready to go at that point.


Great idea.... again, I learn things on this forum that I'm not even thinking about. Thanks.
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