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SEASONING

SEASONING. Seasoning Reducing moisture content appropriate for timber indoors Minimising in-service shrinkage to enhance dimensional stability of product. Removal of moisture from wood Free moisture Bound moisture. Seasoning processes Air seasoning (drying) Kiln seasoning (drying)

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SEASONING

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  1. SEASONING • Seasoning • Reducing moisture content appropriate for timber indoors • Minimising in-service shrinkage to enhance dimensional stability of product • Removal of moisture from wood • Free moisture • Bound moisture • Seasoning processes • Air seasoning (drying) • Kiln seasoning (drying) • Solar kiln seasoning (drying) • Reconditioning • Avoiding shrinkage or collapse during processing

  2. Moisture in wood • Growing Trees • saturated cells - voids filled and water in cell walls • sapwood - hollow cells transmit nutrients and water • heartwood - waste liquids stored in cells • Moisture Content • Growing tree -saturated ~120% • Free water – moisture in cell voids • Bound water – moisture in cell walls • Fibre Saturation Point (fsp) ~25% no water in hollow cells, but cell walls still saturated – all bound water remains • Equilibrium Moisture Content (emc) ~10 to 18% moisture content in equilibrium with service environment – bound water in equilibrium with atmospheric moisture fsp

  3. Moisture in wood • Seasoning • Removes some of the moisture from the wood during processing • Seasoned timber wont lose further moisture in service – minimal shrinkage • Free water • Moisture lost from hollow cells first (to fsp) • Bound water • More energy required to remove moisture from cell walls (to emc) fsp emc

  4. Air seasoning • Ambient air circulating around timber to remove moisture • Stacked timber separated to allow circulation • horizontal spaces • vertical “stickers” or “strips” • often ends wrapped or painted to slow moisture loss through end grain • In hot climates stacks are roofed to stop sun bleaching timber • Inexpensive • no drying energy required • very slow ~6 months to 2 years per 50 mm thickness • large area for storage required

  5. Kiln seasoning • Energy to give rapid drying of timber • Heated air and steam introduced to charged kiln • Circulation of heated air controlled by baffles and fans to give even distribution in the kiln • Kiln Drying Schedules • Temperature, air flow, humidity varied to give optimum drying • Kiln drying schedules varied for different species • Typically 20 - 40 hours to dry to ~12% • Reconditioning • Short duration steaming to repair any damaged surface cells

  6. Solar seasoning • Controlled environment using solar energy • gives faster drying with better control than air seasoning • is less expensive than kiln seasoning • Solar Kilns • Use collectors, fans and baffles to control air movement and temperature • Many designs available

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