Air-Drying Lumber

It’s the low-cost, low-tech way
to dry lumber. Here’s how to do it right.

By Dave Munkittrick

Want a truly cheap and easy way
to dry lumber? Consider air
drying. It’s the most economical
method for removing water from
wood, and when done properly, you’ll
end up with perfect lumber.

Although air-drying is inexpensive
and easy,be aware of these drawbacks:

It’s slow. Depending on the species
and your climate, it can take from 2 to
12 months to bring 4/4 lumber from
green to air-dry (12- to 20-percent
moisture content, depending on your
location).

Air-dry isn’t dry enough for
indoor use. If you’re planning to use
the lumber for outdoor projects, airdrying
outdoors is fine. But if you
plan to use the lumber for interior
projects, you’ll have to re-stack it
indoors and let it dry down to 6- to 8-
percent moisture content.

Loss of material. When you airdry
lumber, it’s not unusual to lose up
to 10 percent or more to drying
defects. Lumber defects occur when
drying is too rapid, which leads to
surface checks and end splits or when
drying is too slow, which results in
sticker stains and discoloration from
fungal growth.Because air-drying is
at the mercy of the weather, drying
rates are difficult to control.

There’s not much you can do about
the slowness or the final moisture
content, but you can ensure that your
lumber has the fewest possible drying
defects. It’s all in how you stack the
pile.Here’s how to do it right:

Put Your Pile in the Open

Locate the stack in an open area
exposed to the prevailing winds.
Avoid shady spots or low areas where
moisture can collect on the ground.

Keep the area around the stack
clean and free of vegetation. Debris
from off-cuts or broken stickers and
sawdust are breeding grounds for
insects that can migrate to your stack.
Control vegetation around an outdoor
pile by laying down landscape
cloth and covering it with gravel.

Click any image to view a larger version.

1. Box-piled lumber yields the most high-quality boards.
The pile should have:

• Straight sides and ends

• Full-length boards on the outside of the pile

• Short boards staggered through the inside of the pile

• Offcuts used as spacers to bridge the gaps caused by short
boards.

2. A slanted roof helps the pile shed water.You can do this in a
number of ways; here we are using stickers on the top that
vary in height to slant the roof to one end of the pile.

Prepare a Good
Foundation

For outdoor drying, the foundation
should be at least 18-in. high. We
used 12-in. cement blocks and 4×6
landscape timbers to keep the bottom
of the pile up off the moist ground
and to encourage airflow through the
bottom of the stack. Level the cement
blocks to create a flat foundation.A
dip in the foundation will telegraph
through your whole stack resulting in
less-than-flat boards. Place the timbers
on 16-in. centers.

Prepare the Boards for
Stacking

First, trim the ends of the boards so
they are a uniform length. Be especially
careful to remove any existing
checks, because they’ll only increase
during the drying process.

Then, “butter” the ends with a
commercial end-sealer (see Sources,
page 98). The money you spend on
end-sealer will be more than paid back in better quality lumber. Make sure the coating is
thick enough to indent with your fingernail.

You may find some variance in the thickness of your
green stock. Sort your wood so that all the boards in a
layer are within 1/16-in. of the same thickness.

Use Good-Quality Stickers

Stickers create gaps between the layers of wood. These
gaps allow air to flow freely through the stack. Make your
stickers from dried wood.They should be straight-grained
and strong, so they can be used over and over again. Standard
stickers should be surfaced to a uniform 3/4 in. x 3/4
in.Use 2- to 3-in.-wide stickers at the ends of the stack. The
extra width helps slow the rapid loss of moisture at the ends
of the boards and makes the stack more stable. Stickers
should be slightly longer than the overall width of the
stack. It is essential that each sticker be place directly in line
with the one below. This creates a vertical column that
transfers all the weight of the stack to the foundation.

Box-Pile the Stack

“Box-piling” is the best way to build your drying stack
(Photo 1). In box-piling, full-length boards are used on the
outside edges, and shorter boards are placed in the interior
of the stack.Fill the voids at the ends of the pile with offcuts
from trimming.

Put a Lid on It

If your stack is outside, it needs a roof to keep out damaging
direct sunlight and rain. You don’t need anything fancy,
although it’s good to have a slight slope in the roof for water
run-off (Photo 2.) We used chipboard covered with tarpaper.
It’s best if the roof overhangs the pile by 6 in.or more.

Weight the Stack

Weight (rocks, cement blocks, sandbags) will lock the
boards in place, helping to prevent warp and twist as they
dry. Plus, it keeps the roof from blowing away.

Control the Wind

To help minimize the effects of the weather, it’s best to
have a tarp that can be dropped down the sides of the pile.
This offers protection on hot windy days when the drying
rate can be too rapid. This is important with hard-to-dry,
check-prone woods like oak and hickory, especially when
the green wood is above 30 percent moisture content.

After you’ve done all you can to protect the quality of
your air-dried lumber, it’s up to nature.

This story originally appeared in American Woodworker June 2002, issue #94