The process of removing excess moisture from wood by drying it after conversion is termed as Timber Seasoning. At the end of reading this article, you probably might have learned the best ways of timber seasoning.
Green timber is saturated with moisture (85% water). Timber with less that 20% moisture content is immune to decay especially dry rot and therefore seasoning aims to reduce moisture content to below 18% for general use, and 12% for use in centrally heated and air-conditioned buildings.
Let us talk about correct seasoned timber in a bit.
Well, a correctly seasoned timber has:
Increased resistance to decay, and
Methods of Timber Seasoning
The two methods of seasoning are Air and Kiln seasoning.
Getting interesting right? Let’s dive deep into the two different methods for a comprehensive understanding.
Air Seasoning (The Natural Method)
Boards are stacked in the open air with sticks (thin strips of wood) between them to allow air to circulate. The stack is raised clear of the ground on piers and has a roof to protect it from the weather.
The ends of the boards are painted, or have cleats (wood or metal strips) nailed across them to prevent the end grain drying more quickly than the rest of the board, as this causes splitting (checking).
Advantages: it is cheap and needs little skilled attention.
Disadvantages: it takes 3-6 days to dry. (Allow one year for every 25 mm thickness of wood before using).
With this method, the moisture content can only be reduced to 15-18% when the natural seasoning method is used.
Kiln Seasoning (The Artificial Method)
Boards are stacked on trolleys with sticks between them, and pushed into a kiln. The kiln is sealed and seasoning proceeds in three stages.
Stage 1: Steam is injected at low temperature to force free moisture out of the wood cells.
Stage 2: Steam is reduced and temperature is increased to dry the wood.
Stage 3: Finally, there is a flow of hot, almost dry air.
Advantages: it takes only a few days or weeks and kills insect eggs in the wood (e.g. woodworm). It is possible to reduce moisture content to below 12%, making the wood suitable for use in centrally heated and air-conditioned buildings.
Disadvantages: kilns are expensive to build and run. It needs more attention and a lot of skills as incorrect drying will ruin the wood.
Hope you got some tips about timber seasoning here?
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