Wood drying

Wood moisture measurement allows to control wood drying. As far as water content is concerned, timber must comply with regulations.

Wood, a wet material

Wood is a hygroscopic material that absorbs or loses water, depending on the relative humidity of air. In addition, wood with a moisture content of less than 30% changes size: wood expands or retracts and can change shape.

Measuring wood moisture content

Drying wood affects :
- its durability,
- its dimensional and structural stability,
- its resistance to moulding and insects. Below a moisture level of 20 %, fungi don’t survive.
Dry wood is also considerably lighter and, therefore, costs less to transport. Drying timber also prepares the timber for gluing or applying finishing products.

Wood drying can be a natural process (storage in aerated premises) or an artificial process (in drying cells). Whatever the process chosen, the timber drying process must be regularly checked, so as to obtain the optimum moisture content in function of what it is to be used for (e.g., for indoor or outdoor use) and species.

Standardized timber moisture content

Carpentry, wooden structures, wood panels, joinery, cabinet making... indeed, these different moisture contents are standardized by National or European Norms. “Wood structures and wooden stairs” must have an average moisture content of no more than 22%. The moisture content of wood used for “constructions and buildings with wooden structures”, on the other hand, must not exceed 18%.

Furthermore, all sawn timber for structural uses, must bear the CE mark. This mark relates mainly to the EN 14081 and EN 14250 standards. The latter states that “when timber is used in manufacturing, the maximum moisture content of wood, and wooden blocks if need be, must not exceed 22 %. Moisture contents must be measured in compliance with EN 13183-2 standards, using an approved electric resistance moisture meter. The moisture content must be checked regularly, “once a day during production or once a shift or for every batch, ensuring that these checks are carried out as frequently as possible”.