Seasoning of Timber

When a tree is newly felled, it contains about 50% or more of its own dry weight as water. This water is in the form of sap and moisture.  Water is to be removed before timber can be used for any engineering purpose. In other words, timber is to be dried.  This process of drying of timber is known as seasoning timber and the moisture should be extracted during seasoning under controlled conditions as nearly as possible at a uniform rate from all parts of timbers. It should also be seen during seasoning that the remaining moisture, which cannot be extracted, is uniformly distributed throughout the mass. If the drying is irregular, the shrinkage of umber will also be irregular and it will set up Internal stresses between the fibres. When these stresses excessive, and are capable of overcoming the cohesion of fibres, the timber warps and'the shakes are formed. 

Wood is a hygroscopic material and absorbs water vapours from air. The dry wood absorbs the moisture from the surrounding air. Now the air humidity is not constant and hence, wood moisture content also varies accordingly.  The fluctuations in wood moisture content from zero to the fibre saturation point cause corresponding volume changes in wood leading to cracking, warping, swelling and shrinkage of wood. 

Wood attains a level of equilibrium moisture content under the given climatic conditions of temperature and relative humidity. By the process of seasoning, the excess of water of timber is extracted in such a way that the moisture content of seasoned timber corresponds to the required moisture content in timber for the environments in which it is to be used. The seasoned timber should be protected from exposure to rain and excessively high humidity.