Timber and Manufactured Boards: notes

Kinds of timber

• Hardwood: comes from broad leaved trees, which usually grow slowly. Examples are mukwa, mahogany and teak.
• Softwood: comes from cone bearing trees, which grow faster. Examples are pine and cypress. It is easy to work and is used for roof trusses and general building.
• Hard or soft: the names describe the kind of tree, not always the strength of the wood.

The tree and conversion

• Growth rings: one ring is added for each year of growth. The heartwood in the centre is dead and strong; the sapwood outside carries water and is weaker.
• Plain sawing: cuts straight through the log. It is cheap and quick but boards cup more.
• Quarter sawing: cuts the log in quarters first. Boards are more stable but waste more wood.

Seasoning and defects

• Seasoning: drying timber to the right moisture content. Air seasoning is slow and cheap; kiln seasoning is quick and controlled.
• Defects: warping and cupping come from uneven drying. Knots are the bases of old branches. Shakes are splits along the grain. Checks are small surface cracks.

Manufactured boards

• Plywood: thin veneers glued with the grain of each layer at right angles, always an odd number of layers.
• Blockboard: a core of strips of softwood between two veneers.
• Chipboard: wood chips glued and pressed. MDF: fine fibres pressed into a smooth board that paints well.