Kiln drying of wood: how the process works

Freshly felled wood holds a large amount of water — often more than 60% relative to its oven-dry mass. To turn it into a dimensionally stable element for furniture or joinery, that water must be removed in a controlled way. That is exactly what kiln drying does: it brings moisture content down to a level at which the wood no longer significantly “works”.

Water occurs in wood in two forms. Free water sits in the cell cavities and leaves first, with no change in dimension. Only once the fibre saturation point (around 30% moisture) is reached does bound water begin to leave the cell walls — and that is when the wood starts to shrink. This is why the most delicate part of drying happens below 30%.

In the chamber, the wood is stacked on stickers so that air flows around every board. Fans ensure even airflow, while air temperature and relative humidity are driven by a predefined schedule. The schedule depends on species and thickness: hardwoods such as oak are dried more slowly and carefully than softwoods, because drying too fast causes surface checks, end splits and internal stresses.

The goal is not merely “dry” wood, but uniform moisture across the full cross-section and across the whole batch. If the surface is drier than the core, residual stresses remain in the material (case-hardening) that later show up as warp during cutting. That is why the cycle ends with conditioning — an equalising phase in which moisture evens out across the section and stresses are released.

We target 8–10% moisture, which corresponds to the equilibrium moisture content of wood in heated interiors. Moisture is measured several times during the cycle and logged per order, not just checked at the end. This ensures every batch arrives within the target range, with the record supplied alongside the goods.

For the customer, consistent drying is the foundation of everything that follows. A correctly dried element keeps its dimensions after installation, does not crack or warp, and behaves the same from batch to batch — which is decisive for the series production of furniture, windows and bed bases.

The advantages of kiln drying are clearest when compared with natural air drying. In the open air, moisture stalls at around 14–18% and depends on the weather and the season, whereas a chamber reliably brings moisture down to 8–10% at any time of year — the level a heated interior requires. The elevated temperature also kills insects and larvae, the cycle takes days instead of months, and the quality does not depend on the weather outside.

That is why kiln drying is the best choice for anyone who processes wood further: predictable material means less cracking, warping and fewer complaints, less waste in production, and accurate lead times throughout the year. Instead of risking raw material whose behaviour you cannot foresee, you get timber that behaves the same in every batch — and that is exactly what turns a one-off order into a long-term, dependable partnership.