# 1st time Air Drying my slabs



## AaronB (Feb 10, 2010)

First let me say that I am air drying my lumber and have no plans to do anything but air dry at least for now.

2 Questions:
I have heard that you need to leave it about 1 year, but there are lots of variables to account for that, and have heard that sometimes the wood can reach its outside moisture content in 6 months.....so....

1.) What should the moisture content be before being brought inside the shop to acclimate and to lower it moisture content more.
2.) What is a good moisture reader, I know there are some with pins, not pins, so what would you suggest.

Thanks


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## BobL (Feb 10, 2010)

AaronB said:


> First let me say that I am air drying my lumber and have no plans to do anything but air dry at least for now.
> 
> 2 Questions:
> I have heard that you need to leave it about 1 year, but there are lots of variables to account for that, and have heard that sometimes the wood can reach its outside moisture content in 6 months.....so....


It takes about a year per inch of thickness to dry to around 12% but if you have a hotter than usual summer it may dry sooner and VV



> 1.) What should the moisture content be before being brought inside the shop to acclimate and to lower it moisture content more.


You can bring it in whenever you like - a more appropriate question is when should you be abel to start working on the wood? That should be when the MC is within a few % of other wood that has been inside your shop for a long time. A more conservative approach is to put the wood in the environment it will finally rest in and let it equilibrate with the MC in that place.



> 2.) What is a good moisture reader, I know there are some with pins, not pins, so what would you suggest.


 The pinless ones are generally more accurate at lower and higher MCs but they also cost more. Basic pin type MC meters are generally OK at telling you whether the MC is the same or different between two pieces of the same type of wood.


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## AaronB (Feb 10, 2010)

thanks for the replies Bob.

I didn't realize that I could bring the wood in anytime, just don't work with it until it reaches the correct moisture content I understand. I just thought I had to leave it outside to air dry where there was air flow around it for a while first.

I will start doing some moisture meter research and see which one I can find I like. I will look at the pinless ones.


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## julian 1973 (Feb 12, 2010)

A great place to dry lumber is in the attic. It will dry much faster than it would if left outside.


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## huskyhank (Feb 12, 2010)

AaronB said:


> thanks for the replies Bob.
> 
> I didn't realize that I could bring the wood in anytime, just don't work with it until it reaches the correct moisture content I understand. I just thought I had to leave it outside to air dry where there was air flow around it for a while first.
> 
> I will start doing some moisture meter research and see which one I can find I like. I will look at the pinless ones.



Its a little more complicated than that. Wood can be dryed rapidly but it takes equipment and knowledge to do so and not loose a lot of wood. Air drying works very well (and has for centuries) but takes a long time compared to a kiln. 

If you have fresh wet wood I suggest leaving it outside covered against rain and sun with plenty of airflow on all sides of each piece of wood. Seal the end grain as soon as possible - when you cut the tree is best. After about 6 months you can move it indoors but keep the air moving around the wood until you know its plenty dry.


.


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## oldsaw (Feb 12, 2010)

Aaron, the absolute worst thing is to have green wood dry too fast. When the initial moisture starts coming down, you will be okay, but there is a lot of "loose" water in fresh cut boards. Losing that too fast will cause stress problems. 

I've got no real place to stack outside, so use "my" side of the garage for that, running a box fan indirectly at first and a dehumidifier, then after a few days, depending on how it's going, direct more of the airflow through the stack. I watch the output from the dehumidifier to determine when the "easy" water is out.

How long? Depends on a lot of factors, which is why you need a meter. I've got a cheap one with pins that has been okay, although I'd like another better one when the budget allows. I bought a few alligator clip wire leads and drove some small finish brads into the sides of some internal boards in the stack so I could monitor when the stack should be redone or even if it needed to be.

It will also depend on species, Oak takes a while, walnut is pretty fast, drying probably twice as fast as oak. With my system, I can get 5/4 oak to usable moisture contents in about 6 months, walnut in 3-4. You soon reach a point where the dehimidifier no longer works, and then you just use airflow.

Clear as mud? But, yes, end coating the boards is critical


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## Mike Van (Feb 12, 2010)

That year to an inch formula is kind of rough, as here from sometime in November to maybe March ? Nothing dries outside. Maybe a little if the suns on it, but I think its next to naught. I sawed a lot of cherry just before Christmas, stickered it up right after. Some of the crookeder [? hard word?] logs, I sawed through and made flitch's. These still have snow on them where it was froze to them, hasn't been warm enough in the shade to melt it off. So, if the snow & ice can't melt, I don't see any drying taking place. Firewood too, ice froze on logs, bucked, split, stacked, covered on top, and still ice on them. Your best drying [here anyway] will be from April on, ending in September.


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## TraditionalTool (Feb 12, 2010)

Mike Van said:


> That year to an inch formula is kind of rough


Mike,

You bet it is. If you read Hoadley's book, "Understanding Wood", there's some better numbers which have to do with species as well as other factors like MC, climate, etc...a Kiln is but one way to accelerate it. Most all are less than a year on average, but in specific climates it will be possible that some wood could even get worse.

Hoadley's numbers give a wide range to dry 1" because of so many factors.


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## BobL (Feb 12, 2010)

Mike Van said:


> That year to an inch formula is kind of rough, as here from sometime in November to maybe March ? Nothing dries outside. Maybe a little if the suns on it, but I think its next to naught. I sawed a lot of cherry just before Christmas, stickered it up right after. Some of the crookeder [? hard word?] logs, I sawed through and made flitch's. These still have snow on them where it was froze to them, hasn't been warm enough in the shade to melt it off. So, if the snow & ice can't melt, I don't see any drying taking place. Firewood too, ice froze on logs, bucked, split, stacked, covered on top, and still ice on them. Your best drying [here anyway] will be from April on, ending in September.



A surprising amount of drying can be obtained at low temperatures provided the cold moist air at the surface of the wood is constantly exchanged. For example a piece of wood will dry faster and to a lower MC in most frost free fridges than at 100F. This is because the maximum moisture fridge air can hold (ie cold air) is much less than 100F air. There is a well known method called freeze drying where things (like wet paper) are placed in freezers to dry them. Wet frozen clothes for example dry quite quickly under cover, so if timber is stacked under cover and are able to get some air flow they will continue to dry. 

The key to both cold and hot drying is to have adequate air flow around the wood. According to the Kiln gurus on the WoodWeb, a basic rule of thumb for any wood drying is one Watt of air moving power per cubic ft of drying space capacity. So a kiln 10 x 20 x 8 ft needs around 1.5 kW of fans just to circulate air through the lumber.


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## Freehand (Feb 12, 2010)

Good stuff as always,Bob.....One thing I've always wanted to try is to hook up an automatic switch with a hydrometer and have the fans circulate only during the most advantageous humidity periods.Trying to save power while optimizing the drying process....


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## Mike Van (Feb 13, 2010)

BobL, I don't know what winter in Perth is like, but here in New England, you will not dry lumber or wood then. Comparing a piece of paper or laundry to a frozen block of wood is?  You just can't compare the two. Water that is frozen solid in the cells of wood is not going to do anything until it thaws. Cut your firewood here too late in the season, you'll learn real fast how wood doesn't dry when frozen. If woodweb says it does, they never lived where there is a real winter.


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## julian 1973 (Feb 13, 2010)

*Have you thought about building a small solar kiln?*

I built a solar kiln and I can easily dry lumber in the dead of the winter here in Chicago. As long as it is 10 degrees warmer than outside it will pull moisture out of the lumber. I dried elm from green to 7% in about 4 months during the winter without a single endcheck and the boards stay straight once they are cut which means low internal stress due to drying. It is much quicker than air drying and it only cost me a few hundred to build.


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## Andrew96 (Feb 13, 2010)

Mike, I don't think some people really understand frozen. In this example, I think you are confusing confirmed lab experiments with real experience. You know....ice can dry  . That's why snow just disappears after a few weeks of no snowfall but constant frozen temps and no sun. Water doesn't have to melt to dry. It can dry while it's a solid. That's a fact that is hard to grasp when you see ice on your lumber and someone is telling you it's drying. Yes..the ice is drying. Without ice on your frozen logs...they are still drying. However, that's a lab experiment. In reality...your wood will be lucky to get 5% loss of MC over a whole frozen winter even when it's not ice covered. Get snow and ice on it...the ice is drying..not the wood. Frozen wood will dry...just not enough to bother thinking about. The colder it gets, the more the ice will dry (lower RH). Still...not worth bothering about. You calling it not drying...since we live in a place where it freezes solid for awhile....you're correct. Not drying for practical purposes. 

Moisture meter: That should be a required tool if you are thinking of using some of the wood you milled. You'll have a ruined project if you use it too soon. 
BTW for us frozen people....moisture meters measure moisture content...not water content so they don't work when the water is frozen (incorrect calibration for frozen water). It's all about electrical current through the wood...I don't have one calibrated for frozen species (if one even exists). Mine states it's accuracy down to 5C. Well above freezing. Mine has pins and a plate. The plate doesn't work on my milled lumber. The surface isn't smooth enough. I'll have to start using some milling chain for that. I'm sure if you look hard enough..you'll find someone has made a chart of resistance measurement for use with a quality meter and frozen wood. I worry about it come spring.


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## Mike Van (Feb 13, 2010)

Andrew, I'll go along with the "not drying enough to bother thinking about" Thank you -


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## jdrum (Feb 13, 2010)

as a kid i can remember milling hemlok in upstate ny in oct. & nov. and when building a shed the frst of may my uncle uncle called it pond dryed. when you drove a nail home you took a shower.

jim


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## BobL (Feb 13, 2010)

Mike Van said:


> BobL, I don't know what winter in Perth is like, but here in New England, you will not dry lumber or wood then. Comparing a piece of paper or laundry to a frozen block of wood is?  You just can't compare the two. Water that is frozen solid in the cells of wood is not going to do anything until it thaws. Cut your firewood here too late in the season, you'll learn real fast how wood doesn't dry when frozen. If woodweb says it does, they never lived where there is a real winter.




A deeply frozen pile of firewood covered in snow also cannot be compared to well stacked and stickered set of lumber. You also hit on a couple of major problems when you said, "cut your firewood too late in the season", and "a real winter".

The liquid in wood is not 100% water, it is a mix of salts and water and the freezing point of the liquid in the wood depends on the woods MC. If the wood is milled too close to winter it will contain a lot of water and the salts will be very dilute so its freezing point will be maybe just a few degrees below that of water. However, if some of that free water has gone, the freezing point of the liquid inside the wood drops to maybe 10 degrees below that of water so that when the outside of the wood appears frozen, because it has ice on it, the inside might not and it is at this point that water can wick out of the wood. If indeed the wood hits a real winter it will deep freeze the wood and nothing will happen. If the wood is well stickered and stacked it can take advantage of the air temp occasionally rising above freezing to warm up a little and cross back into the not frozen zone.

Provided a steady stream of air (even below freezing) is forced through a well stickered stack of wood that is not frozen on the inside, the ice on the outside of the wood will sublime allowing more water to wick out of the wood as long as the liquid inside of the wood is not frozen. The air flow required is significant which is why a pile of fire does not dry in colder climes. The reductions in MC obtained are modest and I agree are not as significant as what can be obtained in summer.

One place on earth where wood does dry (ie from 12%MC to zero MC) extremely well is Antarctica, the reason it dries so well is the airflow is spectacular (ie 2 week blizzards) and that air is also bone dry. 

The other way the ice crystalizing on the outside of the wood is removed is by using a vacuum. Vacuum freezing works more or less in the same way. The reason this is not common with wood is that regulating the cold temperatures and humidities so the wood stays cold and dry but not deep frozen is not easy. Even woodweb says while it does work it is considered easier to use hot kilns.


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## Mike Van (Feb 14, 2010)

BobL, only problem with that plan is last time I checked, there wasn't much lumber being made in Antartica!


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## BobL (Feb 14, 2010)

Mike Van said:


> BobL, only problem with that plan is last time I checked, there wasn't much lumber being made in Antartica!



Yeah - I wonder if they have even one chainsaw on the whole of Antarctica?


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## Freehand (Feb 14, 2010)

Some scientist is cutting ice with one down there as we speak


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