Air drying 4/4 Red Oak

[Cazzhrdwd]

I need to re learn how to dry 4/4 red Oak. I'm using a new Nyle 200m but logs are coming in too fast and they need to be cut up in a reasonable time due to heat and bugs. Plus this new kiln is costing about 250.00 per load to dry.

I'm thinking about a three sided shed with the back to the prevailing wind, 20'x20'. I'll use 1x6 siding butted tight and a double swinging door for the front and tin on top. I'm going to use gravel for now as the floor. Is this alone going to be enough to slow the drying down enough to prevent drying stresses? Should I also cover with burlap?

[YellowHammer]

We dry a decent amount of red oak, and use a 30 foot, four side open shed on concrete.  I personally wouldn't put any sides on the shed, the stacks of drying lumber need good airflow to prevent stain, and I've never had any problems with air drying too fast here in Alabama.  The ends of the boards must be sealed, and it's always a good idea to put the stickers as close to the ends of the boards as possible as they arrest cracking.  I would highly recommend a concrete pad because it's very hard to get gravel dead flat, and the stacks of wood will pick up whatever curve they are sitting on.  I'd also recommend building the roof high, as taller stacks are beneficial is as the weight of wood will help the wood below it to dry flat.  Here's a view looking down one of the aisles of our drying shed.

[MattJ]

I'm still an amateur by quantity standards but I've had good luck air drying oak as yellowhammer shows but I don't have a shed so I top the stacks with sheets of asphalt roofing called ondura. They are just under 4x8 and easy to move by hand, not sharp like metal and reusable. Not very expensive and I get them through the big box stores and overlap them to ensure the wood is well covered and then add bricks to keep them in place.

[GeneWengert-WoodDoc]

I think an open shed is indeed best.  A concrete floor is best, although I have seen gravel.  Billions of board feet are dried in air drying, so an open shed is fine for even 8/4.  In a very windy location, use Shade-Dri on one wall to slow air flow when the lumber is green.  Mount it like a shower curtain so you can pull it aside after a week or two.  As shown, the stacks need to have good clearance at the bottom...I like 8" open.  Also keep packs spaced about 24" edge to edge.

[WDH]

I also air dry a lot of oak under a shed with 4 open sides here in Georgia.  No issues. 

[Cazzhrdwd]

Thanks for the replies, having an open shed is interesting to me. I always figured I'd have problems air drying oak under a open shed from drying to fast when fresh sawn. I can see it working well in the winter, but even in this 90 degree heat you guys still don't have problems?

[WDH]

No.  At night, the humidity gets up to 100%, so the wood is able to come back to equilibrium without too much stress. 

[YellowHammer]

When I first started air drying lumber, I tucked the stacks under some trees, inside a small indention in my wood line.  This spot was always in the shade due to the trees, and never got any wind.  It was, what I thought at the time, a decent place, but it was the kiss of death for air drying.  In the summer it was hot, stagnant and humid, and in the winter the forest floor was covered in wet leaves, and so the spot was perpetually damp, as it never got enough sun to dry out.  My stacks of wood got sticker stain, mold, bugs, all kinds of defects and more than one ruined load went to the burn pile. 

After a couple drying disasters, I picked another spot, the opposite of the first, on the edge of my gravel driveway, in the sun, getting good prevailing breezes.  The new spot was out in the open, dry, comfortable, and a place where I wouldn't mind to set a chair and enjoy the day.  My lumber seemed to really like the spot also, as I never had another problem, everything dried perfect (except maple and poplar, but that is another post ;D). 

The tag line to this true story is that the two original air drying spots, complete opposites in terms of drying productivity, were only about a 150 feet apart.

Since then, I built my present day air drying cover in a similar place because the other was in the way and not big enough.  However, I had learned my lesson as the newer spot in the open, on a slight hill, with concrete, high roof, no sides, good air circulation, catches the afternoon breeze, excellent forklift access, easy for me to walk by and inspect my wood every day, and the lumber dries just fine. 
So picking the right spot is important, and I'd recommend trying out a few to see which gives the best results.  Put out a few stacks in different locations, cover them with corrugated roofing, get them off the ground with blocks or ties, and see which areas perform the best.

BTW, if you think a stack is getting too much wind, just turn it 90° so the wind is not blowing through the stack.

Also, pre drying wood using air drying techniques will save a lot of kiln time and money.

[Cazzhrdwd]

So picking the right spot is important, and I'd recommend trying out a few to see which gives the best results.  Put out a few stacks in different locations, cover them with corrugated roofing, get them off the ground with blocks or ties, and see which areas perform the best.

I do this with poplar which does dry well for me this way. This all got started because I have a load in my kiln now which I'm having a heck of a time getting the moisture to come down. Its an Nyle 200m, its my third load and it has 4500 ft in it. When I put it in the 4 probes went up and down for at least a week. I assume that was because it takes me 2 weeks to saw everything and the moisture could have been different from stack to stack. As the temp goes up to the initial 90 degrees, I assumed that also made things jump around. For another week the average moister indicator stayed just about the same. The third week it finally started coming down but only a 1/2 percent a day, way to little, so I started bumping the temp up a degree each day. After almost a month in there, I'm still at an average of 30% and the water is a fast drip, it should still be pouring out. So after being on the phone with Nyle I checked the difference between the outside shell and inside core. Inside was 30, outside was 15. I'm thinking crap, its slowing down again!!. So I shut off the compressor, poured 10 gallons of water on the floor and bumped the temp up to 120 degrees. We'll see where it is tomorrow. Nyle thinks I have a little bit of casehardening going on which was the reason for the ten gallons.

Which brings me back to air drying, I saw my lumber in a shed that is open on just two sides, none of the lumber sat in there for more than 4 days without being covered, it takes 8 stacks to fill the kiln, once I got four of them done and out of the shed, I would take them outside, cover with plastic and cover with a removal tin roof system I have for the stacks. The reason for the plastic was to be able to put all 8 stacks in the kiln relatively close in moisture content. Nyle thinks even just a few days in wind may have dried it too much, causing the slight casehardening. Which is why I was thinking of putting them in a shed with sides. This may all boil down to having a load of oak that is just difficult, just my luck on the third one!!

I've been kiln drying with another l200 I have for 15 years, but I've probably done only a few thousand feet of oak in all those years, its been mostly poplar, cherry, walnut. I swear I'm having to learn this stuff all over again!! With oak though I can't afford to screw it up. This oak is a 16ft lumber that is wide and very nice, I'd really like to get it right.

[Blackgreyhounds]

Good calls on the Ondura, Shade Dri and cement.  I'm lucky to have ~15 x 7 cement pad outside my pole barn.  I use the wavy plastic roofing sheet from the big box (probably not as durable as Ondura but cheaper and lighter) and bulk burlap instead of Shade Dri.  It seems to work for me.  I would love to have covered drying area like the OP, that is primo, but, I dry about 1-2 MBF/year, mostly for my own personal use or to share with friends.  I just put up a small whack of white oak flitches today.  It's hot, low humidity and there is a breeze, which is about the worst weather to put up green oak.  So, I pulled out all my tricks to slow up the sun and air flow.



  

 

Here's some other piles I have dried similarly.


  

 

Here's a pile of 1250 b.f. of 4/4 red oak that eventually became our floors.  I dried it in the barn with fans.  The lumber came out great, but the acids it gave off rusted/oxidized everything else  in the barn.  Won't make that mistake again.


  

 

Thank you again to the OP for sharing your "best practices."  I'm very much novice at this and I love to hear others practical advice and experiences.

[WDH]

You are definitely not a novice when it comes to properly making a drying stack and stickering lumber.  Your piles are textbook.  Impressive.

[Blackgreyhounds]

Thanks WDH.  I think I'm good for anything 8/4 and smaller.  This last whack I'm working toward learning to dry thicker stuff.

[Cazzhrdwd]

Yes Blackgreyhounds, very nice stacks.

I'm still having trouble getting this 4/4 red oak moving down in moisture. Poured ten gallons on the floor Friday and raised the temp up to 120. It came down 1.8 in moisture but that was it. If you remember the difference between the core and shell were about 15. Yesterday (Saturday) I raised it up to 125, still not much movement this morning (Sunday). Should I put the temp up to 140?

[GeneWengert-WoodDoc]

Anyone who told you that casehardening was causing the wood to dry slowly is 100% incorrect.  Casehardening refers to stress in the wood and not moisture movement.  So, adding moisture to the floor is incorrect and can actually damage the lumber...drying small chEcks deeper.

A moisture meter does not measure above 28% MC with any accuracy at all.  So, when you see 30% MC, it could be 50% and it could lose 3% in a day every week and still read 30% MC.

When we first start drying oak, the surface can be around 20% MC and the core over 70% MC.  I do not know of any reliable drying instructions based on shell core MCs.  So, do not worry about them.

In general, the average MC for a piece of lumber is the MC when the pins are driven 1/4 of the thickness or slightly less.  This is Nader 30% MC average, but oak starts at 75% MC or so.

So, what is the MC now?  If under 20% MC, the standard schedule indicates 140 F maximum.

Are you running the compressor 100% of the time?  If so, 2% loss per day is reasonable, but drier does mean slower.

[Cazzhrdwd]

Anyone who told you that casehardening was causing the wood to dry slowly is 100% incorrect.  Casehardening refers to stress in the wood and not moisture movement.  So, adding moisture to the floor is incorrect and can actually damage the lumber...drying small chEcks deeper.

A moisture meter does not measure above 28% MC with any accuracy at all.  So, when you see 30% MC, it could be 50% and it could lose 3% in a day every week and still read 30% MC.

When we first start drying oak, the surface can be around 20% MC and the core over 70% MC.  I do not know of any reliable drying instructions based on shell core MCs.  So, do not worry about them.

In general, the average MC for a piece of lumber is the MC when the pins are driven 1/4 of the thickness or slightly less.  This is Nader 30% MC average, but oak starts at 75% MC or so.

So, what is the MC now?  If under 20% MC, the standard schedule indicates 140 F maximum.

Are you running the compressor 100% of the time?  If so, 2% loss per day is reasonable, but drier does mean slower.

Yup that's what they said, wow, I'm not sure what to do.

The 200m as you know Gene has probes that are screwed in to the core. They read and average of 36.1. My delmhorst has an outside reading of 15 and an inside reading of 30. I seem to be at a point where its not coming down anymore, I'm wondering how to keep it moving.

By the way, it was explained to me that casehardening causes the wood to close up on the outside, thereby not letting the moisture to escape, the cure for that is water on the floor to soften it, with more heat, thereby letting the moisture to flow again.

[beenthere]

Cazz
Google and read up on the progression of casehardening.

As I understand it, the surface of a wet board dries too fast causing surface shrinkage and surface checking. Then later, when the center of the board dries below 30% and shrinks, the surface cracks close up and often cannot be seen. Damage is done in the early stages of drying and "healing" those early surface checks can't be reversed later on.

[Denny]

Drying schedule should be based off of the MC of the sample as a whole, not the core or not the shell....  altho I gotta admit I do like to see my cores under 30% before I move the temp to 120.  This is why I like my pinless meter over my pinned meter, I get the whole picture with the pinless, while my pin meter, a Delmhorst, uses insulated pins so only the tips are reading MC, I can drive the pins into the core and get a core reading or just drive em in 1\4 inch and get a shell reading. But I don't even use the pin meter at all anymore, If I need to check my shell and core, I do an oven test. If I need a quick MC check, after the lumber is out of the kiln, I use my pinless meter. I never ever check my kiln samples with a meter, I weigh everyday and calculate the MC.  I trust my Merlin pinless meter, but when it counts, I cut the lumber and do an oven test.

Ive often seen RO cores of 30% and shells of 15% and when the lumber is finished, they're both right there at 6-8%, but I have a large pre-dryer and don't air dry at all, the pre-dryer constantly dries the RO 24 hrs a day. While the core does dry in my pre-dryer, the shell dries faster every time. Proper air drying should keep that core and shell MC closer together because at night/early morning the RH outside 'relaxes' the RO and "equalizes" the shell and core somewhat.

I like to see a daily MC loss of 2% once the RO is under 30-40%.

[Cazzhrdwd]

That's interesting Denny, with my Delmhorst pin type, I just take a core reading, then a shell and it averages it for me. As far as the oven test, I'm sure its accurate but with the pin I can take readings all over the kiln. The probes are the ones that have me irritated. They're consistently more higher than my Delmhorst.

So what should I do to get this load going again?

[Denny]

"So what should I do to get this load going again?"
I can't give you the advice you ask for because I have no experience with dehumidification drying. I operate "conventional" kilns.

"As far as the oven test, I'm sure its accurate but with the pin I can take readings all over the kiln."
It doesn't get any more accurate than an oven test. I find my pin meter to be cumbersome and nearly impossible to get the pins in the lumber near center of the boards... because they are in a pack and I hate to just to test the ends of boards that are sticking out of the pack.  With my pinless meter I can slip the slim little meter in the bolster spaces between packs and get a reading. You gotta remember anything above 25% and the meters lose there accuracy.

Do you de-hume guys "equalize" your kiln charges ?  I've found that the times when my core is a good bit wetter than my shell, the core catches up with the shell's numbers when the sample gets below fiber saturation point, around 25 to 30 percent. Once I get my samples in the high single digits, I "equalize" the charge for 3 to 4 days and this is when my shell and core MC spread becomes more equal.  I'm equalizing at 170-135 which if I recall off the top of my head is around 39% RH or 5% EMC.
I also "condition" my RO as a final stage. This puts moisture back into the shell, which contributes to a balanced shell and core number. 

I don't know how you de-hume guys dry, so all l my info might be a moot point :-)

[GeneWengert-WoodDoc]

Equalizing is done at 5% EMC, or 5.5% or 6.0%, etc. depending on the needs and requirements of the customer.  A dehumidifier can achieve the required EMC (if the kiln is tightly built) but seldom is run over 150 F.  Cooler temperatures take longer than your 170 F to equalize.

The most critical time for lumber drying is the very early stage...oftentimes this is above 50% MC.  All defects except cup form at this high MC, so that is where they must be prevented by controlling the drying rate precisely.  Unfortunately, this is also when a moisture meter does not work well enough to be useful, so the so-called "sample board" method is the only option for the best control.  However, permanent pins put into the wood but very shallow, will start working (give reliable readings under 30% MC for the shell) even though the average MC for the lumber is still well above 30% MC.  As time goes on, the dry-zone of under 30% MC goes deeper and deeper, so pins that are at a depth of 1/4 of the thickness can be used.  These "1/4 deep" pins give the average MC of the piece and every kiln schedule and operating procedure uses the average MC, not the shell and also not the shell- core difference.  However, with pins, we never are really confident in the MC numbers at higher MCs  (but under 30% MC) when drying.  The reason is that we often have a gradient from the surface to core of 20% MC.  This gradient is over a distance of 1/2", so each 1/16" depth of the pins is over 1% MC difference.  The pin depth is not precisely controlled (to 1/32") so we introduce errors.  The bottom line is that it is not too reliable to use a moisture meter system to run a kiln drying green wood.  Once we are at lower MCs, the meter can be used, but the critical part of drying is over, so close control of conditions and precise MC values are not needed.  Finally, at the end of drying, the meter can be used to establish the final MC, using temperature corrections.  However, we do know the permanent pins often give variable final MC readings.

The pinless meter can be used, but variations in wood density cause big variations in MC.

Neither meter does well when brought into a humid kiln, as condensation on and in the meter create issues.

Bottom line:  the sample board method using the oven drying of small sections initially is the best when precise MC values are needed.

[Cazzhrdwd]

The water is finally starting to move again. I left it at 120 degrees with the average still at about 30%. Its been coming down about 1% a day.


I'm sure the oven dry is the best way, its just seems cumbersome. The best way for me seems to be controlled air drying for a month or so then in the kiln to finish up.

What percentage of degrade do some of you expect on 4/4 red oak?

[Den Socling]

It sure is nice to operate vacuum kilns where you don't need to mess with samples!

[Cazzhrdwd]

It sure is nice to operate vacuum kilns where you don't need to mess with samples!

Good point.

What kind is yours?

[Denny]

"The water is finally starting to move again."  Well thats good news. You need that heat to drive out that water now that your at FSP. Be carefully going too hot so close to 30%.... you can bet there's higher than 30% boards somewhere in your kiln charge. My schedule and most RO schedules call for 120 at 30% but I like to see my samples a coupla ticks below 30% before I move up to 120 degrees.

"I'm sure the oven dry is the best way, its just seems cumbersome."
My oven samples stay in the oven for close to 24 hours at 210-215 degrees. If I need a quicker oven sample reading I throw the pieces in the microwave and depending on the MC, they're bone dry within minutes.

"It sure is nice to operate vacuum kilns where you don't need to mess with samples!"
So do you guys use a probe system that stays in the lumber the whole drying cycle to monitor the MC ? I weigh and calculate 40 samples every day from my kilns and then another 10 to 15 samples from my pre-dryer. At one time I operated 17 kilns and two pre-dryers so I weighed and calculated a minimum of 85 samples every day  .

[Den Socling]

Cazzhrdwd, you could say my kilns are home-made. I own http://www.vacdry.com/

At the end of a drying cycle, we simply hold chamber pressure (vacuum), humidity and temperature. The wood will continue drying below FSP to the final MC as set by the final temperature. If I want Red Oak to be 7%, I stop at 140'F. If I want Hard Maple baseball bats to be 6%, I stop at 150'. It works every time.