Puunkuivaus

Puunkuivaus, or wood drying, is the process of reducing the moisture content of timber to a level suitable for its planned use. Dry wood is more dimensionally stable, bonds with glue and finishes better, and is less prone to decay, warping, and fungal growth than green wood.

Drying methods include natural air drying, kiln drying, dehumidification drying, and vacuum drying. Air drying relies on ambient conditions and stack spacing to remove moisture gradually, with low energy use but long durations. Kiln drying uses controlled heat, airflow, and humidity to accelerate drying and to manage stresses such as case hardening, making it suitable for large or high-precision batches.

Several factors influence drying rate and quality, including wood species and density, thickness and grain direction, initial moisture content, end-sealing on the cut surfaces, stacking pattern (stickers and gaps), and the surrounding climate. Proper moisture distribution and avoidance of rapid shifts reduce risk of cracking, warping, and checks.

Moisture content (MC) is the percentage of water in wood by weight. Target MC depends on end use: interior timber often aims for around 7–12%, while exterior or climate-sensitive applications may require higher or controlled MC up to the equilibrium moisture content of the environment. Measurement is typically done with handheld meters or laboratory methods.

Process steps generally include initial trimming and planing, stacking with spacers, monitoring MC during drying, and conditioning or equilibration after reaching the target MC. Modern operations may use automated sensors and computer-controlled schedules. The practice has historical roots in traditional forestry and has evolved with industrial kiln technology.