NC State Extension

Drying Green Lumber

by James B. “Jim” Kea
Area Extension Forestry Agent – now retired
Thursday, February 9th, 2006

With all the storm and beetle kills, many landowners have small volumes of useable timber that is not marketable through conventional logging methods.

An alternative to burning or letting the critters have it is to have it sawn into useable lumber. There are still a number of “ground” mills that have become stationary. These mills often use conventional circular saws that turn a quarter inch of wood into sawdust with each pass. New band mills cut as little as one sixteenth of an inch into sawdust. Both mills now come in portable versions that actual go to the log. Give me a call for the location of a mill nearby.

Conventional mills move the log through the saw. The new mills move the saw along rails through the stationary log. Long timbers cut from this rail system are not readily available at the local building supply. Mills also come with attachments for cutting shingles and lap board siding. Mills can actually cut firewood length logs as well as 65 footers. Boards as thin as one quarter inch can also be shaved from logs.

Lumber cut this way can be used green if allowances are made for drying shrinkage. Some joints are actually designed to tighten as wood dries. Wood normally shrinks little if any length-wise. It will shrink more along the rings than across the rings. This causes cracks or checks to normally develop across the rings.

Wood can be dried on the farm or in the back yard in small amounts a number of ways. Double duty for two seasonally used farm structures can speed the process.

Bulk Tobacco Barn: (1) Check the maximum weight that the perforated floor can carry. Pine lumber weighs approximately five pounds per board foot (1″ X 12″ X 12″). Hardwood would weigh between 5 and 7 pounds per board foot. (2) Weigh a sample board while it is green. Mark it as a reference board for determining when your lumber is dry. (3) Paint the ends of lumber to reduce splitting. Use oil based paint. Lumber should have 1″ stickers (ie. tobacco sticks) placed every 2 feet of each layer. Place stickers directly over those in the previous layer. Leave about an inch between boards in each layer. The pile should be as level and flat as possible. A foot wide chimney needs to be left in the center and a cover such as plywood placed on stickers on top of the pile. The idea is to spread the air flow from the chimney out between the layers. (4) The first day run at 120° dry bulb and 110° wet bulb. The second-day run 120°dry bulb and 105° wet bulb. The third fourth and fifth days run at 130° – 140° dry bulb and 90° wet bulb or less with no water added. Continue at this schedule if not dry for one more day. Thin lumber (less than 1″ thick) may need weight on top to reduce twisting and warping of the top layers. Stack this lumber in lower layers of random size lumber with large timbers on top. Eggs and adults of wood boring insects should be killed with this schedule. (5) Wood should weigh three pounds or less per board foot when dry at 20% moisture content. Moisture content will change to match relative humidity. (6) Dry lumber can be stored without stickers, but must be kept flat. Store in a dry place.

Greenhouse: (1) Use the same painting, weighing and stacking technique as with the bulk barn. (2) Keep sides rolled up high enough to maximize air movement while keeping rain off the lumber. Space stacks to take advantage of prevailing wind. (3) Lumber will take at least 60 days to dry to 20% this way. Other covered buildings with good air flow will also work, but without solar power the drying time will be closer to 6 months. Weigh the sample board every 30 days or use a moisture meter. (4) Restack and store in a dry location. (5) Wood boring insects may be a problem with air dried lumber. Once moisture content is below 20% the chances of infestation diminish. Monitor for sawdust. Heat at 120° for 24 hours to kill eggs and adults. Insecticides may create problems when sanding or sawing. (6) Wood craftsmen often air dry prize lumber for 6 or 7 years to ensure uniform moisture throughout.

Revised 2/16/2006.

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