Air drying different species

[True North]

Hey guys. I was wondering if someone could give me some advice.

I would like to cut several species this summer and sticker it outside (covered with metal) to dry for several months to a year, and then kiln dry it in the future. I understand that some species will last outside better than others. For red oak, popple, sruce, and maple, will it be ok to dry it outside like that?

Also, if the trees are cut in the spring/summer after the sap is running, will I have to worry about mold if they get stickered right away? Also, with those species I have been told that if they are cut to late into the spring or summer, you need to saw them right away. How fast is right away?

[petefrombearswamp]

Hi True,
If you sticker it at the ends and every 2' and cover no problem except, in my experience ,Hard maple which will sticker stain.
I sticker it for about 3 days and then re- stack moving the stickers slightly. I make my own stickers for this in a I-beam cross section configuration to aid with air flow.
When I only have a few boards of HM,  30 or so i line them up vertically along my nearby pole bldg for again 3 days so the surface dries then stack them as outlined above.
Labor intensive but worth it.
It is important to get the stickers exactly above each other to prevent undue strain.
Good luck,
Pete

[True North]

Thanks, Pete!

[Brad_S.]

I like to keep my oaks (white especially, red to a lesser extent) shielded from breezes or heavy air flow for at least a couple of weeks to prevent surface checking. White oak has very little tolerance for dry breezes flowing across it. I have had issues in as little as a day after stacking.

[woodmills1]

direct sunlight even when it is cold will cause oak to rapidly surface check

[Okrafarmer]

I'd like to ask more about this topic, as a lot of wood we will start sawing will need to be air-dried. We have a lot of SYP, ERC, red and white oaks, red and silver maple, tulip poplar, sweetgum, hickory, beech, sycamore, and cherry around here, as well as less common species such as walnut, honey locust, black locust, hemlock, persimmon, and others. No doubt we'll end up milling all this stuff and more over time.

I've been told the rule of thumb is one year per inch on hardwoods for drying time. I assume this means ends painted, and stickered in a sheltered location open on all sides.

 How long for pine and cedar? Do you put something heavy on top of the stack to hold it down? Can you do multiple species in the same stack, and what about the drying of various slices of the log? Some are saying on here not to use the pith at all, as it will cup and bow beyond all recognition. But what if you have it held down near the bottom of the stack? Are some species more forgiving than others when it comes to getting straight lumber while air-drying?

[Tom]

Okrafarmer,
That paragraph has volumes of answers awaiting it.  Unfortunately, there is no "pat" answer.

Yes, a drying shed is the best thing to use.   Direct sun, water,  and the accumulation of water within a stack are its worse enemies.

Generally speaking, sealing the ends of the boards is the way to go.  Actually, sealing any end grain is the way to go.  That could mean knots, runouts (where the grain runs out of the side of the board), crotchs, etc.  Usually it is just the ends, and time can be saved by sealing the end of the log before sawing.  Many folks like the sealant to be on the end and an inch or two back on the sides of the board too.

Different woods dry at different rates.  Pine in North Florida will reach nineteen percent in 6 or 8 weeks, while Eastern Red Cedar is so stable that it can almost be used straight off of the saw, in an emergency.

Putting something heavy on the top of the stack might help the boards on the top of the stack, but the weight of the stack is what you are looking for to help the majority of the boards.  That is one reason to keep stacks narrow and tall.   The other reason to keep a stack narrow and tall is to ensure that the flow of air is strong enough to remove the moist air from the stack.  It even makes a difference as to the direction you point the stack to the prevailing winds.

When a board decides it is going to bend, all the weight of the stack isn't enough to hold it down.  I've seen an errant board lift the weight of an entire stack, leaving boards alongside it free of the sticker.

Yes, You can dry multiple species in a single stack, but it isn't recommended because it becomes a management problem.  Drying multiple species in Kiln is frowned upon because you are imposing drying schedules on the stack based on a single specie and there is no one-shoe-fits-all kiln schedule.
Air drying is more forgiving, because it is relatively slow, gives the wood a chance to normalize (remove stress) and is dependent upon ambient moisture content, not artificially induced oven-dry air.

Stories on the Pith.  The pith is the center of the tree and is defined by the line left behind by the growing tip as the tree grew.  The pith is not of the same consistency of the rest of the log and neither are the first 3 to 5 rings surrounding it.  That is why it is usually cut out of expensive boards.  Here again, that is not a steadfast rule and you will find the pith left in many boards, even after the furniture is built.

Cupping is when a flat-sawn board (what you are calling rift) bends toward the bark side and edges lift.  It is not a result of leaving the pith in a board, but rather the the difference that the board moves dependent upon the direction of the growing rings.  Vertical grain, like you find on the outside edges of most boards does not cup, it crooks (bends to the side).  So the opposing forces on each side of the pith is what keeps the crook in check.  That is why so many people value quartersawn boards over flat-sawn.  The problem with only selecting one grain orientation is that you ignore the value of the other orientations.  You limit yourself to driving a Chrysler even though a Ford or Chevy might fit the job better.  Or you will only drive a yellow car, regardless of its make because you can find it in a parking lot best.

Yes, some species are more forgiving than others.  I've already mentioned cedar and Pine.  Sycamore and Gum are notoriously difficult to dry and keep straight.  White Oak is more difficult to dry than Red Oak.   But it isn't just the species, it is the configuration of the board as well.  Flat-grain dries at a different rate and difficulty than vertical grain, of the same species.  Special cuts, that open up end grain, like crotches, bowl blanks, and boards cut from crooked logs require special drying techniques.

The forum is full of information on each of these and more.  While it might be possible to address select problems with a post, you will get a better  general education by using the search function of the forum and reading threads on these subjects.   I'm not trying to put you off, but the subject is so vast that a general answer is not very informative and a detailed answer would have no end. 

[SwampDonkey]

I'll keep the math out of it  , but as you may or not know, wood moves when below fiber saturation (no longer green). That is when wood looses bound water, not from the loss of water in cell lumins. A particular species could have twice as much weight when wet than when the wood is oven dried, depending on species. This would mean it's MC% is 200%. If the point of fibre saturation was 30 % and your wood sample has a moisture content (MC) of 80 %, and you dried the sample to 40 %, you still have no shrinkage movement. But this notion is only an ideal situation as wood does not dry evenly, and some species are more vulnerable to surface checking as was mentioned for white oak. Eastern red, eastern white and western red cedars (coastal and interior) and interior Douglas fir don't hold a lot of water and are quick to air dry. You can make kindling from fresh eastern white cedar here and it's pretty much ready to burn, more so with the old stuff. White ash is not all that wet green either, not like black ash is.

The denser hardwoods (Sp. Gravity in green condition > 0.55) usually take more drying time.  My personal preference, none scientific, is to air dry all woods at least 3 years. Each shrink and expand cycle with the moisture in the air at different times of the year,  diminishes the shrinkage. In other words, the greatest movement is from fresh cut to that first drying below saturation to it's target MC. If your always below fibre saturation and your wood MC changes because of the environment around the wood, than the wood always moves (expands/contracts) because moisture flow in and out of wood cell walls wants to be in equilibrium with the surrounding air. Wood is a Hygroscopic material. Also, radial shrinkage from sap to heart is less than at a tangent to the new growth increment. Sometimes it's half for some species and others it's only a small difference. With flat sawn lumber I think we go with 1/16" of shrinkage per 2" width to 19 % MC from green as rule of thumb. In this case it's tangential shrinkage we are most concerned with. In quartered material your more concerned in the thickness of a piece moving because the tangential direction would then be up and down instead of across the width.

[Okrafarmer]

Thanks, that gets me started. I can only imagine the sheds I'd have to build to air-dry stuff for three years!

[WDH]

You will not need three years in South Carolina.  Figure about 120 days for yellow poplar, cherry, red maple, and black walnut.  (95% of the air drying will have occurred by that time in your climate).  My experience is that after 6 months on the sticks, there is no further appreciable moisture loss.  I know this because I use a moisture meter.  Oak takes longer.  It takes me at least 6 months to get 4/4 red oak to 15%.  I have some white oak that has been on the sticks since December 29, 2009, and it is still running about 20% moisture.  It should reach 15% sometimes this fall, so figure at least 9 months for 4/4 white oak.  As you go north, the drying slows as the temperature is not usually as high and the winters are much colder and wetter.  We get faster air drying in the south.

If you are going to be air drying a significant amount of hardwood, you will be well served to buy a good moisture meter to check your lumber.  You will need to spend at least $200 and up to $400 to get a good meter.  However, it is money well spent.  I have a pin-less Wagner that runs about $400.  It is great because you just lay the meter on the wood (there are no pins to make holes).  The drawback is that you have to set the specific gravity on the meter for each species that you are checking.  That is not a big deal if you are drying a lot of wood because you need to be familar with specific gravity of the various woods anyway.  The meter comes with a chart that gives you the average specific gravity of the commonly used woods, so it is pretty easy to set the meter for the correct specific gravity.

I have had problems with yellow poplar and red maple getting a stain from the humidity being too high.  One issue that I had was my stacks were too wide at 5 to 6 feet wide.  The wood was under a shed open on three sides.  Just having one side closed to full wind and air flow can make a difference.  I have also gotten some sticker stain in yellow poplar and maple.  There has been a little sticker stain in some of my red oak, but it generally planes out.  Keeping the stacks tall and narrow with several feet between stacks is key like Tom pointed out in his very informative answer.  I know shoot for a maximim width of 4 feet or a 6 foor wide stack with the center one foot of the width left open to create a draft to draw out the moisture and move it away from the lumber.  Fans can help move the air, but that only works on some species like poplar, pine, and cedar.  Fans and too much air flow will ruin oak as there will be checking and honeycombing of the wood from the shell drying too fast for the core.  Oak is better slow and easy.  Especially white oak since the pore structure of the wood guarantees that water will only move out of the wood very slowly, much more so than red oak, and much much more slowly than woods like walnut, cherry, and yellow poplar.

Generally, I have found walnut and cherry the easiest to dry.  No sticker or gray stain, no molding, and not much checking.  Maple is a bear since it will gray stain in a heartbeat if the humidity is too high.  All it takes is a couple of days of stagnant air flow and high humidity, and the maple will gray stain bad.  Gray stain in maple is an oxidation reaction in the wood and is not because of a mold or mildew.  The oxidation reaction occurs at high heat and humidity with no air flow to move the moisture out of the stack, so that is why the highest quality maple is usually immediately put into dry kilns green and dried on a precise schedule to keep the gray stain at bay and the wood nice and white.

Sorry for the long discourse.  Drying lumber is the hardest part of the lumber making process in my experience  .

[SwampDonkey]

We don't likely need 3 years here either, but gives me piece of mind. In our north the air is cold and dry in winter as evidenced by the low dew point and less precipitation.  Takes about a foot of powder snow to make an inch of water. The far north is even dryer than here and a lot less precip. But water moves slower in wood when it's frozen and crystalized.   Wood being a poor conductor of heat, don't expect much vaporization of frozen water inside the wood beyond a couple  inches on the end of sticks from the sun hitting the wood pile. Relative humidity is a bad indicator of moisture, it only indicates when your getting close to precipitation out of the air, when dew point and air temp converge. Our RH for this area averages about 70 % year round according to records kept by NOAA for Caribou, Maine.

Moisture meters are definitely a nice addition to the toolbox. I've never invested in one and should. Too cheap I guess.

I have had some stain troubles here, but that was wood laid too long on the ground. And white pine that never had good air flow. White pine is quite a challenge, it's best cut in the late fall or winter to get good results unless ya shove the lumber in the kiln right away and not let it lay in log form in the warm seasons.

Similar to walnut, butternut is easy to dry and butternut doesn't hold a lot of water when green. Cherry has been easy to dry in my experience as well, just a little trouble around juvenile and heart for warp and check which should be expected.

[WDH]

I have had some trouble too with cherry getting splits in the juvenile wood.  Most times, juvenile wood acts juvenile  . 

For those of you who are not wood technologists, juvenile wood is the wood that comprises the first 5 to 10 years of growth in a stem.  The kind and amount of cellulose that makes up the cell walls is different than the wood that forms as the stems matures.  So, wood created in the first few years of growth is different that the later wood in subsequent years, and that is a main reason that you get splits in boards that contain the pith since the pith is the center of the stem when the plant was a baby.

Young wood is just like teenagers, kinda brashy  .

[SwampDonkey]

The lumber sawed from white oak for a water wheel on a mill at Kings Landing Historical site was air dried for 4 years before being used.

[Mad Professor]

Use plastic corrugated on oak. Oak stains with metals