Materials and Timber Technology
This domain tests how well you understand wood as an engineering material: its anatomy, its relationship with water, the defects that downgrade it, and the panel products that replace solid timber. Questions normally pair a definition with a practical decision - which board, at what moisture content, for which component.
Structure and species
- Softwoods come from conifers (pine, spruce, fir, cedar); hardwoods from broadleaved trees (beech, oak, ash, walnut, meranti). The split is botanical, not physical: balsa is a hardwood.
- Cross-section: bark, cambium, sapwood (pale, permeable, less durable), heartwood (darker, extractive-rich, more durable), pith. Each ring has earlywood (wide, thin-walled, weak) and latewood (dense, strong).
- Density at a stated moisture content drives strength and screw holding: pine about 500 kg/m3, beech about 720, oak about 700 at 12% MC.
Moisture
- MC% = (wet mass − oven-dry mass) / oven-dry mass × 100.
- Fibre saturation point is about 28–30%. Above it, water fills the cell lumen and the wood does not move; below it, water leaves the cell wall and shrinkage begins.
- Equilibrium moisture content (EMC) is the balance reached with the surrounding air. Heated interiors in Cyprus sit near 8–10%; humid coastal winters push towards 12%.
- Shrinkage is anisotropic: tangential is roughly twice radial, longitudinal is almost nil. Flat-sawn boards therefore cup away from the pith; quarter-sawn boards stay flatter and show figure.
- Seasoning: air drying to 15–18%, kiln drying to 8–10%. Case-hardening, honeycomb and end checks are kiln faults.
Defects
Live and dead knots, shakes, checks, resin pockets, reaction wood (compression wood in softwoods, tension wood in hardwoods, both causing distortion on machining), fungal decay, insect attack, blue stain (cosmetic).
Panel products
Plywood (odd number of balanced plies, WBP glue for exterior), blockboard, particleboard (cheap, poor edge screw holding, must be edged), MDF (homogeneous, routes well, swells badly when wet), OSB, hardboard, HPL and melamine-faced boards.
Worked example
A beech offcut weighs 520 g. Dried to constant mass at 103 °C it weighs 455 g. MC = (520 − 455) / 455 × 100 = 14.3%. Interior furniture needs 8–10%, so machining now means the board will shrink and joints will open. Mass at 10% MC = 455 × 1.10 = 500 g, so about 20 g of water must leave the piece first.
Traps that cost marks
Confusing moisture content with equilibrium moisture content; quoting density without stating MC; assuming hardwood means hard; assuming all plywood is waterproof; pushing meter pins along the grain or into cold timber, which under-reads.
Use the formula triangle, state units, and always link the number to a decision (machine it, dry it, reject it).