Wood Shrinkage

When wood is dried continuously, water is driven from cell walls and changes in cross-sectional dimension, namely shrinkage may occur.

Wood shrinkage may occur in three mutually orthogonal directions i.e. along wood axis (longitudinal), along radial direction (radial) and along the tangent to the radius (tangential).

Tangential shrinkage is generally two times as much as the radial shrinkage. Among the three directions, longitudinal shrinkage is often negligible. Volumetric shrinkage, which defined as the summation of the shrinkages in all directions is around 1.6 times the tangential shrinkage.

Shrinkage is dependent of the species, grain pattern, cell wall thickness and the arrangement of cells. In general, sapwood shrinks more than heartwood, and hardwoods shrink more than softwoods. The loss of water from the ends of wood is higher than from its sides. This can lead to the bending of wood, and eventually longitudinal crack when the bending stress exceed the tensile strength of wood.

Shrinkage rate can be reasonably assumed constant until the wood is dried completely.