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Seasoning

Seasoning. Seasoning is the reduction of the moisture content of wood. Seasoning is also the controlled drying out of timber. About 50% of the weight of newly-felled tree is water. Seasoning. Reasons for Seasoning: Seasoning helps to save the wood from splitting.

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Seasoning

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  1. Seasoning • Seasoning is the reduction of the moisture content of wood. • Seasoning is also the controlled drying out of timber. • About 50% of the weight of newly-felled tree is water

  2. Seasoning • Reasons for Seasoning: • Seasoning helps to save the wood from splitting. • Dry timber (< 20% MC) will not be attacked by fungi • Dry timber is less likely to be affected by shrinkage or distortion • After seasoning, timber will be lighter, harder and stronger. • Seasoning produces timber that is easier to work with.

  3. Seasoning 13% - (Australia)

  4. Relative Humidity • “The amount of moisture in the air at a given temperature, compared with the maximum amount of moisture the air could hold at that same temperature”. • There is a certain amount of water vapour in the air at all times, depending on the weather, season, etc.

  5. Moisture Content • “The amount of moisture present in the wood is shown as a percentage (%) of the weight of the wood when dry” • Wood is hydroscopic so moisture changes will affect it so it will soak up or let out moisture until it has reached a balance = Equilibrium Moisture Content (EMC).

  6. Natural Seasoning • Also known as Air Seasoning. • Planks of green timber are laid down on battens and have a gap between them to allow air to circulate. Stickers or skids are the small pieces of wood that allow the air travel between the planks.

  7. Natural Seasoning • The stack should be: -Covered to prevent rain damage while the planks dry out. -On a clean dry site -All planks of the same species and similar sizes should be kept in the one stack -The ends of the boards should be protected from the sun to prevent excessive drying-out.

  8. Natural Seasoning • Advantages of Natural Seasoning -No expensive equipment required -Small labour cost once the stack is made -Not wasteful of energy • Disadvantages of Natural Seasoning -Slow drying rate -Large area of space required -Dependant on the weather -Rate of seasoning cannot be carefully controlled -Only seasons to a MC of 18% - 22%

  9. Kiln Seasoning • The lumber is placed in large kilns (ovens) where temperatures, humidity and drying rates are controlled • There are 2 types of kiln: -Compartment Kiln & Progressive Kiln

  10. Compartment Kiln • Timber is stacked similar to that in natural seasoning only it is on a trolley which runs on rails. • The kiln is closed before steam jets in the walls, ceiling and floor release heated steam. • The timber is allowed to heat up but not dry out.

  11. Compartment Kiln • The relative humidity of the kiln is reduced (controlled)while the heat is maintained. (This allows moisture in the wood to evaporate gradually) • Fans circulate the air around the kiln. • Air vents allow moist wet air out and fresh air in.

  12. Progressive Kiln • The progressive kiln is a continuous kiln. The timber goes through the various stages of drying as it moves through the kiln on a trolley. The drying process is the same as that for the Compartment Kiln.

  13. Kiln Seasoning • Advantages of Kiln Seasoning -Quicker due to higher temperatures, ventilation and air circulation -Achieves a lower moisture content -Provides greater degree of control during the drying process -Allows more precise rates of drying -Allows uniform circulation through the stack -Control over moisture content and rate of drying can be achieved -Artificial defects can be controlled • Disadvantages of Kiln Seasoning -It is expensive -Requires supervision by a skilled operator -Is dependant on energy

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