Wood moisture question
#9
I just bought 2 live edge slabs of walnut to make a table top. I've gotten the moisture down from the low 30's to the high 20's with a fan. Pretty slow work. We live in Georgia where our humidity is pretty high. How low does this need to be before I start working with it?
Thanks!
"Some glue, some brads while the glue dries, and that's not going anywhere!"
Norm
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#10
(05-30-2024, 01:42 PM)plharrison Wrote: I just bought 2 live edge slabs of walnut to make a table top. I've gotten the moisture down from the low 30's to the high 20's with a fan. Pretty slow work. We live in Georgia where our humidity is pretty high. How low does this need to be before I start working with it?
Thanks!

What's your indoor RH?  If you're running AC it's likely 50% or lower.  50% RH is 9% MC, so it would not be good to take a slab in the high 20's% MC into that environment.  A guy I know who cuts and sells slabs claims anything below 20% is good-to-go.  On the other hand, I've heard from several people that slabs they bought from him cupped and/or split.  The outdoor equilibrium moisture content in GA according to the Forest Products Lab is about 13% most of the year.  It sounds like you have the wood indoors.  I suggest you sticker it outdoors, in the shade with a roof on top but open on the sides/ends, in a location where the wind will blow through the sides.  You didn't say how thick the slabs are, but 4/4 stock should be air dry in a couple more months.  8/4 will likely take until Fall, maybe even late next Spring.  

I would not bring them indoors until they are well less than 20% and preferably below 15%.  Uncontrolled force drying of thick slabs never turns out well.  

John  
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#11
I hope you're young... it's going to take a while...
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#12
Thanks John. Not sure what the relative humidity is in my basement shop where they are currently. They are 1 1/2" thick. I should have mentioned that. I realized this was going to take a while which is fine. Not planning anything that needs to be done immediately. I do have an outdoor covered porch on the second level with a lot of room to leave them outdoors. Maybe I'll give that a try. A Georgia summer has very high humidity so that will be interesting.
"Some glue, some brads while the glue dries, and that's not going anywhere!"
Norm
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#13
I'm not young! LOL, I knew this was gonna take a while!
"Some glue, some brads while the glue dries, and that's not going anywhere!"
Norm
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#14
Even with a high RH outside, if you have air moving over it whether that is a study breeze or a solar-powered fan, you can still get dehumidity of the wood down.
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#15
If you've got a basement, I'm assuming you're in the N GA mountains, correct?

Anyway, I'm in NE FL and air dry EMC here is 16% +/- depending on the wood species. IOW the lowest we can get air dry is 16%.

I don't work with slabs but I know they are notoriously bad about cupping. The thing is not so much the absolute MC but equal exposure both sides. I would sticker them with thick stickers like 2" to give plenty of air flow.

Personally I wouldn't be comfortable with 20%. I think the only way you're going to get there is a) move the slabs inside a climate controlled room or b) kiln dry. You can determine which option is best for you, but I do know there are heat driven as well as solar kiln plans out there and they aren't hard to build.

Some depends on how you're going to use them.


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#16
(05-31-2024, 07:09 AM)plharrison Wrote: Thanks John. Not sure what the relative humidity is in my basement shop where they are currently. They are 1 1/2" thick. I should have mentioned that. I realized this was going to take a while which is fine. Not planning anything that needs to be done immediately. I do have an outdoor covered porch on the second level with a lot of room to leave them outdoors. Maybe I'll give that a try. A Georgia summer has very high humidity so that will be interesting.

I looked up the EMC for the cities listed for GA in the Forest Products Lab document on that topic. 

[Image: AP1GczPYq6kPXcUY4orJCwvbxtV6qTwurws5V4G9...authuser=1]

It's hard to believe it's that low in Savannah in the Summer, but the FPL is a reputable outfit.  

I don't know what the RH is your basement, but I would bet it's pretty high if you aren't running a dehumidifier.  You can still get drying at 70% RH, even higher, if you move air across the wood.  This is exactly how kilns work.  You start out at high RH and then lower it as the wood dries.  Indoors/outdoors, doesn't matter, but moving air over the wood is needed in any case to make it efficient.  6/4 walnut will air dry in my area in less than a year.  FWIW, the EMC where I live is not much different from where you are, at least according to the FPL data.    

John
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