Air dying

[Kasba]

I want to air dry some maple for wood working but I was told that is not useable unless it gets down between 6 and 8%, so does that mean the only way it is useable is if I get it finished off in a kiln?

[beenthere]

Not sure where you plan to use the finished product of your woodworking, but I wouldn't put complete faith in whoever "told" you that air dry maple wasn't usable.  Maybe there is more to the story?

[Ianab]

Ideally you want your wood to be as close to it's final moisture content as possible before you build stuff with it, especially furniture.

Now if you air dry wood outside, it will generally only dry down to 12-14% moisture. If you build with that, then bring it inside where where it dries down to 6-8%, it's going to shrink a bit. Maybe enough to open up some gaps in your fine woodworking.

To get around this (without a kiln) get your wood air dry, then bring the rough boards in and finish drying them inside (attic, spare room, heated workshop etc). Let the boards dry there for a month or so, and they will be around the equilibrium moisture for that particular environment.

Then you build you furniture, and the wood wont move much in use.

Main reason to use a kiln is because it's fast and controlled. Put wood in, run kiln for a couple of weeks, and you KNOW the wood is perfectly dried. Air drying, you have to take your time and let the same thing happen naturally, which is going to take months.   

[gfadvm]

I have built a lot of tables, chairs, and boxes with 15% air dried wood of several species. I have had one failure in all my projects (flat sawn sycamore warped- I knew better!). I always try to allow for wood movement in the design. Your milage may vary.

[GeneWengert-WoodDoc]

In choosing a drying place, appreciate that 30% RH will achieve 6% MC after a while.  Ok if you are not in a hurry.  Otherwise, get a location that is maybe 25% RH.  Hotter makes the wood dry faster, but the final MC depends only on RH.  Because in North America, most homes run around 30% RH in the winter, that is why we like the dry final values.  Indeed, bring the wood into the heated shop after air drying and it will begin to dry to these lower values right away...a few weeks in the shop before use can be awesome.

[woodworker9]

Just to add to the discussion, I've been building furniture and cabinetry almost exclusively with "air dried" lumber for the past 15 years.  Typically, I hate purchasing kiln dried lumber because I always had trouble with the available suppliers in my area.  More often than not, case hardening was frequently an issue.  On top of that, the only really well equipped hardwood supplier near Chicagoland didn't sell rough stock.  They planed both sides of the timbers before offering them for sale.  Nobody in that place ever heard of a jointer-first approach to preparing wood, because most of the stuff was twisted and crooked just enough to make joinery a pain in the butt.

Like has already been stated, the only thing that matters is that the wood is in equilibrium with it's surroundings.  I have a drying shed filled with rough  sawn lumber, but I also have a lumber rack on the wall in my shop that holds about 900 bf of lumber.  I have shelf brackets rated at 2500 lbs. each, 4 per row, and I have 4 rows going up to the ceiling.  I keep enough lumber inside the shop on these racks in the different species that I work with so that I always have well acclimated lumber, ready to be worked.

Of course, none of this has anything to do with setting pitch on softwoods or killing bugs.  For that, a kiln is going to be necessary to get the temperature up.  I don't have these problems, as I keep my stacks bug free and I don't work with softwoods.

[rwachtell]

Many things to consider with lumber when it comes to shrinkage and green board usage. 

1) How wide is the board/boards you are using?
2) How much and what kind of joinery in the work will you have?  Some types are more sensitive to movement then others.
2) Are your boards flat grain?
3) Are your boards quarter sawn grain?

Some things can be made with green lumber and when they dry will show no ill effects from shrinkage.

Here are some examples that describe the potential problems a bit.

Keep in mind that when I use the term "green" I am referring to a board with Moiture Content more then say 10%

A cutting board made from one board will show little effect if it is made with a green board and dried slowly. May check on the face or end if not dried slowly and it may cup.

A cutting board made from two green boards joined together down the middle will end up OK too. They can move out and back away from the joint as needed. This may have about the same risk of trouble as the above board.

Three green boards joined together might begin to show more problems.

A picture frame that only has end grain joinery i.e. 45 degree miter cuts can be made with lumber greener then a wet sponge and as it dries the only thing that will happen is that the rectangle will become a little smaller.

With this said the more moisture content you have in wood the more likely you are to have a problem.
If the MC is very high say 25% in the single board cutting board ... it may cup very badly if it is flat grain but not so badly if it is quarter sawn grain.

Its also important to realize you never see anyone  living in Arizona posting on any of these air drying forums  ...  "Can I use my air dried lumber for furniture making" 

And yes cactus are not the only trees that grow in Arizona.

[warren46]

I built this desk out of air dried maple several years ago and have not seen any movement.  I did not measure the moisture content but I suspect it was in the 12 percent range.  I did construct the desk using good design so the wood could expand and contract with out distortion of the piece.  Just be careful to design so the wood can move without damage to the furniture.


 
As you can see there are some wide panels of solid wood that need to move.

[Glenn1]

Warren,  that is a very nice looking desk..... 8)

[beenthere]

I agree on the desk, and good to hear about the stability you have over the years.

[Ianab]

Would be interesting to measure the top and see how much it has moved since it was built.

Doesn't affect the desk structure in any way as long as you used good design, it would just be interesting to know.

Also, if your air dried wood survives one year inside, it's as dry as it's ever going to get, and should last for decades more. Any movement after that will be seasonal, and that will affect any wood, no matter how it was dried.

[GeneWengert-WoodDoc]

We do know that wood will shrink as it looses moisture.  The shrinkage is zero in length most of the time, but about 1% size change with a 4% moisture loss across the grain...teak is less and oak is more, so this is just a rough estimate.  Quartersawn lumber is 1% for 6% moisture loss.

We also know that almost all of North America has an humid exterior environment that will dry wood to 12 to 14% MC after a long air drying process.  Further, we know that almost all homes and offices in North America have an interior environment equivalent to 6% MC in the wintertime and 9% MC in the summertime.  This means that a 24" wide piece of wood will shrink about 1/4" to 1/2" in going from air dried 13% MC to 7% MC interior.  Note that the speed of drying or the temperature does not affect total shrinkage appreciably.

We also know that a heated shop, an attic, and many other wood storage and processing locations are low humidity so air dried wood can quickly dry to a lower value than the moisture level that results when air drying.  So, air-dried wood quickly can become wood that is close to kiln dried wood moisture contents without actually being in a kiln.  Such drying, which includes drying in a heated room, has been well documented for centuries (Colonial Williamsburg) and even in DRYING EASTERN HARDWOOD LUMBER.

[Outer Rondacker]

Warren46 that is on nice desk. Good Job!

I have used maple one year after sitting outside under cover and not had an issue. I feel the time of year you bring it in makes a big deal. This is just something I feel. For example, If I bring in lumber from the outside stack in the hot summer air it has a lower MC then if I do it in the wet mud seasons.  This is do to the RH.

Ah do not listen to me I just wanted to post about the nice desk.