Wood contains different quantity of moisture that depends on whether the tree is felled and immediately processed or the timber is already kiln dried to required moisture content for final usage.
The oven-dry resp. absolutely dry density test of timber can be made only by means of a special drying oven at 103°C +/-2°C plus final weighing on a precision scale. The weight of wet wood is highest, while absolutely dry wood is lowest. That means the weight (more precisely the mass) depends on its current moisture content.
Remarks: For logistic matters this fact is very important because of optimal transport (cargo) utilization.
1) Fresh cut (green) means spruce and silver fir at 35-50% moisture content in the center of the log (heartwood). 100-150% moisture content in sapwood means an average moisture content of 55-70% related to absolutely dry content. Similarly, the moisture content of beech and oak are 70-100%.
2) Open air-dried means 12-15% moisture content for central Europe.
This table shows that the density, commonly named ’specific weight of timber‘, is influenced by the current moisture content. Spruce and silver fir have the lowest whilst oak has the highest density.
Remarks: The ranges are based on the area, location and environmental conditions in which the tree was grown. Different densities within a type of wood can be identified by the annual rings. In Scandinavia and Russia e.g., the growth of the tree is slow due to strong winters resulting in narrow annual rings. In moderate climates as in Central Europe the distance between the annual rings are significantly wider. Different weather conditions during growth period of the tree influence distance and shape of the annual rings additionally.
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