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Topic 2 of 6 · Form 5

Conversion, seasoning, preservation and forestry

Through-and-through (plain) sawing – economical, more figure but more distortion; quarter sawing – stable boards, attractive ray figure, more waste; tangential sawing.

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  1. PDFConversion, seasoning, preservation and forestry – Wood Technology and Design notes (ZIMSEC A Level)47.2 KB

Conversion

Through-and-through (plain) sawing – economical, more figure but more distortion; quarter sawing – stable boards, attractive ray figure, more waste; tangential sawing.

Seasoning

  • Air seasoning: stacked with stickers, under cover, good airflow – cheap, slow, limited to air EMC.
  • Kiln seasoning: controlled temperature and humidity (kiln schedules) – fast, reaches low MC, kills insects; risk of case hardening and checks if too fast.
  • Solar kilns: low-cost option suitable for rural sawmills.

Defects

Natural (knots, shakes, reaction wood), seasoning (checks, splits, warping, case hardening, collapse), and biological (fungal decay, termites, borers).

Preservation

Preservatives: creosote, copper chrome arsenate (CCA) pressure treatment for poles and fencing, boron treatments for indoor timber. Methods: brushing, dipping, hot-and-cold open tank, vacuum-pressure impregnation. Handle toxic preservatives safely.

Forestry and sustainability

Indigenous woodlands (teak and mukwa in Matabeleland, miombo) are under pressure from clearing, fires and illegal logging. The Forestry Commission manages state forests and promotes plantations; sustainable harvesting, certification (FSC) and reforestation protect the resource.

Exam tip: Explain why seasoning matters by linking moisture content to stability, strength and resistance to decay.

Check yourself

  1. What is case hardening?
  2. Name a preservative method used for fencing poles.
  3. Give one advantage of quarter sawing.
Show answers
  1. Stresses in kiln-dried timber where the outer layers set while the core is still wet, causing distortion when cut.
  2. Vacuum-pressure impregnation with CCA (or creosote treatment).
  3. Boards are more stable (less cupping) and show attractive figure.
Next topicManufactured boards and adhesives

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