Materials: timber, manufactured boards, adhesives and finishes
Materials: timber, boards, adhesives and finishes
This domain tests whether you can select and justify materials for a woodwork job: timber classification, conversion and seasoning, defects, manufactured boards, adhesives and finishes.
Core rules
- Softwoods come from conifers; hardwoods from broad-leaved trees. Hardness is not the same as botanical class: balsa is a hardwood.
- Conversion: through-and-through sawing is fast but produces wide, cupped boards; quarter sawing gives more stable, figured boards but more waste.
- Seasoning reduces moisture content (MC). Air drying is slow; kiln drying is faster and more controlled. Timber for interior furniture is usually dried to about 8–12% MC in service.
- Defects include knots, shakes, splits, waney edge, insect attack and fungal decay. Shrinkage causes cupping, bowing, twisting and spring.
- Manufactured boards: plywood is strong and stable due to crossed veneers; blockboard has a softwood core; MDF machines and finishes well but produces harmful dust; particleboard is cheap but edges crumble; hardboard is dense and thin.
- Adhesives: PVA for interior wood-to-wood; cross-linking PVA for limited moisture; contact adhesive for laminates; epoxy for strong gap-filling bonds; urea formaldehyde for assembly and veneering.
- Finishes: oil and wax penetrate; varnish and lacquer form a film; paint hides grain and protects. Prepare the surface before finishing.
Worked example
A bathroom vanity door needs a stable, moisture-resistant panel with a painted finish. Choose plywood rather than particleboard because crossed veneers resist movement and moisture better; seal edges. Use cross-linking PVA or epoxy for the frame, not ordinary PVA. Finish with a moisture-resistant paint or spar varnish, sanding between coats.
Traps
Calling all hardwoods 'hard'; ignoring MC; using interior PVA outdoors; sanding MDF without extraction; applying thick coats that run or trap dust.