1.3. The air-seasoning of timber
The sawn timber has to be stacked for drying until its moisture content goes down to 15 percent.
Drying is by evaporation: the air is able to absorb moisture, and moving air dries more effectively.
An open, well-drained site should be selected, the foundations solidly laid with provision for cross and end ventilation, and at least 450 mm above the ground.
The boards should be stacked 25 or 50 mm apart to form vertical flues.
Each layer of boards is separated by spacing strips set from 600 to 1200 mm apart to enable fresh air to enter from the side. The spacing strips have to be set in a vertical row.
The quality of the lumber depends a lot on how it was stacked for seasoning.
A waterproof covering should be placed over the stack to protect it from sun and weather.
The time taken for air seasoning depends upon several factors, such as type of timber, size of boards, time of the year, site on which the stack is built, and the method of stacking. Roughly it takes about twelve month for each 20 mm timber-thickness.
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