The Seasoning of Timber

"Seasoning" is the name given to the methods of drying timber.

There are two methods by which timber can be dried:

 

  1.  Natural drying or air drying.

  2.  Artificial drying or kiln drying.

Natural Drying/Air Drying

  • Air-drying is the drying of timber by exposing it to the air.

  • The technique of air-drying consists mainly of making a stack of sawn timber (with the layers of boards separated by stickers) on raised foundations, in a clean, cool, dry and shady place.

  • Rate of drying largely depends on climatic conditions, and on the air movement (exposure to the wind).

  • For successful air-drying, a continuous and uniform flow of air throughout the pile of the timber needs to be arranged.

  • Coating the planks with any substance that is relatively impermeable to moisture can control the rate of loss of moisture; ordinary mineral oil is usually quite effective.

  • Coating the ends of logs with oil or thick paint, improves their quality upon drying.

  • Wrapping planks or logs in materials, which will allow some movement of moisture, generally works very well provided the wood is first treated against fungal infection by coating in petrol/gasoline or oil. 

Artificial Drying/Kiln Drying

  • The process of kiln drying consists basically of introducing heat.

  • This may be directly, using natural gas and/or electricity or indirectly, through steam-heated heat exchangers, although solar energy is also possible.

  • In the process, deliberate control of temperature, relative humidity and air circulation is provided to give conditions at various stages (moisture contents or times) of drying the timber to achieve effective drying.

  • For this purpose, the timber is stacked in chambers, called wood drying kilns, which are fitted with equipment for manipulation and control of the temperature and the relative humidity of the drying air and its circulation rate through the timber stack.

  • Kiln drying provides a means of overcoming the limitations imposed by erratic weather conditions.

  • In kiln drying as in air drying, unsaturated air is used as the drying medium.

  • Almost all commercial timbers of the world are dried in industrial kilns.

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