# Storing kiln dried wood



## reprosser

I have a sawmill and will have a kiln up and running before too long (I hope...)

Once I get the wood kiln dried, how should I store it while waiting to use it? 

If I leave it in the (unheated/uncooled) shop - I think it will soak up moisture from the air? It gets pretty humid here in SC.


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## Daren

Yes in an unheated/uncooled space the wood is going to reach EMC (equilibrium moisture content) again after kiln drying. That varies obviously with the weather, but around here (and it's about the same where you live) EMC runs between 10% and 12%. I sell/use wood once kiln dried/now EMC exclusively, my wood is stored in a barn. You just have to let it acclimate in a conditioned space for a little while before using it on fine joinery, get it back closer to 8%. There are many factors that play into the stability of the wood during moisture change, species and the way it was milled are the 2 biggies (meaning 1/4 sawn is more stable than flat sawn). Some species move very little even from fresh off the mill (30%+) to kiln dried, others shrink and swell more with very little moisture change.

Here are a couple calculators to help you figure out what you are going to deal with. 

EMC plug in the temp and RH (relative humidity) to get the % wood that has been sitting for awhile is going to be.

Wood shrinkage Use your EMC as the starting % and figure in the winter with the furnace running a piece of furniture is going to get under 7%.





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## reprosser

Thanks for the info and calculators.

So, if I kiln dry, then store for a while (a day?, a week?)in the shop it should be at EMC, and I can bring it indoors (air conditioned) to let it acclimate before taking it out to the shop to build with. I assume it will hold the lower MC for the few days(?) of building. Once a finish is applied, it should greatly reduce the speed of moisture exchange.

Hmmm
If I let it air dry (no kiln) it would also be at EMC. Almost seems like I don't need to kiln dry - just let it acclimate before use? I know that is not right :blink:...maybe it is more stable after kiln drying and getting back to EMC.


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## Daren

It's complicated...like today (and the last several days) it is right at 70 degrees and the humidity right now is 35%. Using the calculator that puts my kiln dried wood right back to 7% EMC, in theory. You are right this is not a fast happening thing so a few days doesn't make a big difference, but weeks do.



reprosser said:


> If I let it air dry (no kiln) it would also be at EMC. Almost seems like I don't need to kiln dry - just let it acclimate before use?


Well that's sorta right too. You could air dry for a year,(4/4 stock, 8/4 obviously longer) then bring it in the house for a couple months...if you want to wait that long and have room in the house to store wood. For a couple small projects a year if a guy has properly air dried wood/can bring said wood into a heated-dry space to acclimate he could get by without a kiln (on most species, not all)



reprosser said:


> ...maybe it is more stable after kiln drying and getting back to EMC.


And yes. Since the kiln dried wood was dried very controlled/steady it is more stable in the few % changes that happen seasonally. It's a cell structure thing.




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## buroak

another tip in storing kiln dried lumber is to dead stack it. this will slow down change to EMC


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## reprosser

buroak said:


> another tip in storing kiln dried lumber is to dead stack it. this will slow down change to EMC


I assume "dead stack" is stacking without stickers? That would seem to make sense. I could also seal the ends to help prevent moisture change.


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## John D in CT

"Almost seems like I don't need to kiln dry - just let it acclimate before use? I know that is not right :blink:...maybe it is more stable after kiln drying and getting back to EMC".

It's my understanding that air-dried wood (unless perhaps it's in the Mojave Desert) will never be as dry as (properly) kiln-dried wood, no matter what the process (dehumidication, steam heat, solar, vacuum, microwave .....). Kiln drying will remove water that's locked inside cells that won't readily come out just by having the wood exposed to the air. I don't think that any amount of air drying will ever bring wood down to 6-8% MC. By virtue of the fact (I hope it's a fact?) that the KD wood has had a lot of the intra-cellular moisture removed (that air drying can't), it will always have a lower MC than air-dried lumber both before and after it has been acclimatized in (say) a 60% humidity environment, since the water in the air won't readily (if at all) find its way back into the cells.

In wild-a$$ numbers: wood that has been KD'd to 6% might end up at 12% after prolonged exposure to 60% humidity, and wood that has been air-dried to 12% might end up at 18%.

Shorter answer: I think KD is always better than air-dried (for most species anyway), and will be more stable in its final environment.

As always, I'm open to correction.

I'm also going to be building a kiln soon to dry 8/4 oak for a product I'll be marketing. Getting anyone with a kiln interested in drying thick stuff is very difficult. I'll probably go with a commercial dehumidifier or two, fans, and electrical resistance heat (for setting the pitch in pine). I'll probably also get a steam generator for the case-hardening step. Looking forward to cheap, high quality lumber. I'm in the tree removal business in CT, so obtaining oak logs is the easy part  

Good luck with your kiln.

***

Just found an interesting site about the vastly different EMC rates depending on what part of the country you're in.

http://www.woodfloorsonline.com/techtalk/US_moisture_map.html

I definitely would not want to be a hardwood floor installer in Salt lake City, Utah. 14.6% EMC in January, 7.1% in July. Sounds like "callback" to me.


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## Daren

John D in CT said:


> As always, I'm open to correction.



No you understand and explained it pretty well, welcome to the forum.


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## John D in CT

Daren -

Thanks for the validation. Halfway into that, I started to ask myself "Hmmm ... am I BS'ing? I think this is accurate, but maybe my sources weren't correct". Always nice to know I'm not spreading misinformation.

Thanks for the welcome - nice site you have here; it's in my favorites now and I'll be stopping by a bit, I'm sure. I also like the DIY site very much.

By the way - that looks like a Husqvarna in your picture - but I think we can be friends anyway. :laughing:

All kidding aside, even though I'm a Stihl guy, one of my favorite saws ever was my Husky 242 w/ 18" bar that I used for heavier stuff while climbing. Great saw; man it packed a punch. I also LOVE the 346; legendary. 357, 372, heck they're all great. Ford vs. Chevy, same deal. Try a Stihl 441 if you never have; smooooth as silk.

Best regards, John D.


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## Daren

John D in CT said:


> By the way - that looks like a Husqvarna in your picture


Close, it's cousin Jonsered (same difference really, all the parts interchange) an old 2095 turbo. 94 cc saw. I just use it for bucking big ones or ripping. It is heavier than say a Stihl of the same power. I would not want to lug mine around in the woods at 18 lbs dry/no bar. But it's done a lot of hard work for me around the mill. I don't really fell trees, just mill them.



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## bikeshooter

After reading this and other threads concerning storage of kiln dried wood, it looks like it's better not to dry too much at one time - that is 'dry as needed' and build is better than dry a large pile and deal with storage problems. Hope I worded that clearly :blink:


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## ETWW

Drying wood in a heated kiln also has the advantage of killing any bug infestation present. The wood can then be treated with something like Timbor to prevent re-infestation.

Unless the wood is heated to 130 degrees or more, any existing infestation will not be affected by the application of a topical treatment (Timbor).

You are correct that storage of kiln-dried wood can be a problem since it will eventually reach EMC with it's environment. The average RH of the Eastern half of the US is 60% which equates to a 12% MC...even higher in coastal areas and lower in the Mountain West and Desert Southwest.


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## lawrence

Is there some reason I cant leave it in the kiln?...mine will be 30 x 30 with a cement floor so room is not an issue. I build cold storage facilities once in a while and was planing on useing the same setup...if not I will divie it up and cool the back side for storage


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## ETWW

lawrence said:


> Is there some reason I cant leave it in the kiln


Leaving the dried wood in the kiln is a good solution as long as you don't need the kiln for drying another charge. I've got 300 bft of Walnut I'm leaving in the kiln and another 300 bft air drying. With the high temps and low RH's we've had this summer, even the air dried stuff is pretty dry...below 10% MC.

Even storing the lumber indoors in an unheated space will help keep the MC lower than storing outdoors. That's because indoors, it doesn't see the high relative humidity that is present in the mornings...near 100% in most areas.

Another option for preserving low MC's is to wrap the dead-stacked lumber with plastic and tape the ends closed. If the lumber isn't exposed to moist air, it can't absorb moisture from that air. (recommended by Gene Wengert) 

It would be wonderful if we could all store/work our lumber in a climate-controlled environment but that's not affordable for most hobbiests and some pro woodworkers. There's always a trade-off and sometimes we have to work the wood at a higher MC than preferred. That just means taking precautions to allow for wood movement and taking more care in wood selection for certain pieces (like using straight-grained wood for stiles and rails).


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## ETWW

John D in CT;162707
Kiln drying will remove water that's locked inside cells that won't readily come out just by having the wood exposed to the air. I don't think that any amount of air drying will ever bring wood down to 6-8% MC. By virtue of the fact (I hope it's a fact?) that the KD wood has had a lot of the intra-cellular moisture removed (that air drying can't) said:


> There are three factors that affect drying rate; relative humidity, heat and air flow regardless of the drying method used.
> 
> You are correct that air-drying, in most areas, won't bring the wood down to 6% - 8% simply because the average relative humidity is too high. In desert areas or the mountain west, like Denver, where the RH can go as low as 1%, air-dried wood will certainly get that dry and even dryer. Most areas, however, will see only 12% MC from air drying.
> 
> Wood cells contain free water and bound water. The free water is held within the cellular cavities and is the first to go when drying wood. When all the free water is gone and only the bound water (water that is chemically attached to the cell wall) is left, that's known as the fiber saturation point. Unless submerged, the wood can never re-gain moisture above the FSP because it's already saturated. The average FSP is around 28% MC.
> 
> Moisture in wood moves from the area of highest MC to the area of lowest MC. Heat facilitates that movement and air-flow removes it once it reaches the exterior of the wood.
> 
> Once wood is dried to a certain MC, say 8% and then exposed to a 10% EMC, it may only regain moisture to 9% MC. It's called a hysteresis effect.
> 
> Any of Gene Wengert's publications (especially "Drying of Hardwood Lumber" or Hoadley's "Understanding Wood" are chock full of accurate, scientific information on the drying process.


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