Air drying of hardwoods

      Basic information, and where to find more of it, on air-drying green lumber. 1998.

by Professor Gene Wengert

Q.
The factory is using 30 m3 of hardwood per month. The types of hardwoods used are: teak, acajou, and iroco. Thickness varies from 30 to 80 mm.

Is there a method using open air drying to get the humidity of the wood from 60-65% down to 30%? They have about 4 to 5 months time for this part of the drying process. The relative air humidity in Togo is on average 70 to 80%. The air temperature during daytime is 35 to 40 degrees Celsius.

A.
Your question and comments have led me to believe that you are confusing moisture content of the wood and the relative humidity of the air. A RH of 80% (typical of islands) is equal to 16% MC; and 65% RH is 12% MC.

Your question is about air drying being able to reduce the MC of wood down to 30% MC. Yes, standard air drying will reduce the MC to about 25% MC in several months (inch thick lumber) and over a long enough time period, eventually to 16% MC. The key is to keep the rain off the lumber. In the rain, the lumber will dry too slowly and be subject to mold, decay, warp, discoloration, and so on.

Does this help? There is an old publication from the US Department of Agriculture, Forest Products Lab about air drying. You might find the information helpful. It is out of print, but if you have access to the WWW, try to search for Powell's Book store in Portland, OR which has old used books about wood.

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

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