Lecture 3 - wood

Historical & Cultural Context

• Whakairo (traditional Māori carving)

  • Earliest & most culturally significant timber use in NZ.

  • Example shown: mid-1800s tōtara cottage with thatched roof.

• Colonial & modern interiors

  • Timber used for flooring, wall/ceiling linings, rafters, furniture, through to contemporary engineered products.

Sustainability & Global Forest Issues

• Tropical hardwood forests threatened by farming, cropping, large-scale logging (image: intact kauri vs clear-fell site).

• Key environmental con

  • Deforestation ➔ biodiversity loss, carbon release, cultural impacts.

• Forest Stewardship Council (FSC)

  • Independent certification of "+well-managed forest".

  • All specified timber should carry an FSC label.

Tree Anatomy & Material Properties

• Basic cross-section (centre ➔ outward):

  • Heartwood (harder, older, durable)

  • Sapwood (younger, active fluid transport)

  • Cambium

  • Bark.

• Hardwood vs softwood ⇨ cellular differences (microscope slide shown) & broadleaf vs conifer leaf morphology.

• Pros

  • Renewable, high strength-to-weight, machinable, aesthetic warmth.

  • Biodegradable (end-of-life, carbon sink during growth).

• Cons

  • Rot, borer, fire, dimensional movement due to moisture.

Sawing Patterns & Grain Behaviour

• Plain/flat sawn, quarter sawn, rift sawn diagrams → each yields distinct:

  • Appearance (growth-ring angle).

  • Stability: warping, cupping, moisture release paths.

  • Cost & yield trade-off.

Key Species (NZ-centric)

• Native: rimu, mataī, tawa, tōtara, red beech, silver beech.

• Exotic plantation: radiata pine (Pinus radiata) – dominates construction; redwood trials (Rotorua) historically unsuccessful commercially.

• Australian imports: eucalypts, jarrah, spotted gum, etc.

• Global imports: walnut, mahogany, maple, ash, oak.

Surface Conditions / Mill Finishes

• Rough-sawn → external framing, weatherboards, landscape timbers.

• Planer-gauged → slightly radiused arrises, closer tolerance.

• Dressed (DAR) → exact dimensions for joinery.

• Profiled sections: skirtings, architraves, tongue-and-groove (T&G), weatherboards.

Dimensional Standards (NZ-S3601)

• Nominal framing "4x2" = $50\times100\,\text{mm}$ (rough-sawn).

• Dressed size ≈ $45\times90\,\text{mm}$.

Structural & Appearance Grades

• Stress grades $F1 \rightarrow F11$ (higher $F$ = higher allowable stress).

• Appearance grades: Clear (furniture), Select, Merch, Box (formwork).

Treatment Classes (Hazard, NZS3640)

• $H1 \text{–} H1.2$: interior, protected; $H1.2$ resists insects.

• $H3.1$: exterior above-ground, intermittent wetting (fascia, weatherboards).

• $H4$: ground contact (posts).

• $H5$: critical structural in-ground (house piles, deck posts).

Modified Solid Timbers

• Example: Accoya (radiata pine acetylated with vinegar-based acetic anhydride).

  • Benefits: increased hardness, stability, decay resistance.

  • Caution: residual acidity → specify stainless-steel fixings (galv/zinc corrode).

• Other processes: thermal modification, furfurylation.

Engineered / Laminated Timbers

• Glue-laminated members (glulam)

  • Grain aligned, long spans, curves possible.

  • Finger-jointing evens out weak points.

• Visual example: mixed beams, veneered panels, steam-bent handrail.

Joinery Highlights & Iconic Designs

• Mortise-and-tenon bridging a butt joint (furniture demo).

• Steam-bent masterpieces

  • Thonet No.14 bentwood chair – highest sales ever.

  • Jigs & steaming shown.

  • Frank Gehry “Easy Edges” laminated strips (1990s).

• Press-moulded plywood classics

  • Eames LCW $\text{(Low Chair Wood)}$, Lounge 670.

• NZ designer: David Trubridge slatted luminaire (cold-formed veneer).

Veneers

• Thickness: $\approx0.5\text{–}2\,\text{mm}$, bonded to plywood/MDF/particleboard.

• Rotary-peeled vs sliced veneer ➔ differing figure.

• Lay-up patterns

  • Book match, slip match, diamond match.

  • Specify same-tree sourcing for colour/grain consistency (same terms used for marble slabs – see previous Stone lecture).

Plywood

• Cross-laminated veneer sheets; strength ↑ with thickness & odd-layer symmetry.

• Grades: face/back letters $A, B, C, D$ (e.g. $AC$ interior lining standard).

• Common sheet: $2400\times1200\,\text{mm}$; up to $3000\,\text{mm}$ available.

• Good plywood edges require even, void-free lay-up (specify if exposed).

• Finishes: clear, stain, melamine-faced.

• Structural + aesthetic applications (full wall/ceiling interiors illustrated).

Particle-Based Panels

• Chipboard/particleboard (NZ: "particleboard")

  • Large chips + UF resin; substrate for laminate, cabinetry.

  • Swells/blows if wet.

• Strand/flake board (OSB)

  • Longer flakes, structural flooring/wall bracing; rough edge → conceal or detail carefully.

• MDF (medium-density fibreboard)

  • Fine fibres + resin; stable, machinable, laser-cut friendly.

  • Visual edge sometimes celebrated, sometimes hidden.

  • Formaldehyde concerns → low-VOC or E0 boards exist.

• High-density MDF variant → tool blunting; now used for industrial moulds.

• Softboard (pinboard) – low-density, acoustic.

• Hardboard (Masonite)

  • Steam-exploded fibres + natural lignin bind; low VOC, good sustainability.

Cork & Other Natural Products

• Cork bark: flooring, acoustic wall tiles, novel furniture.

  • Warm, resilient, accepts stains.

Flooring Systems

• Solid T&G plank flooring (villa typology) – $\text{nail-fixed to joists}$, lifetime durability.

• Engineered/composite wood floors

  • Structural ply/particle core + $5\text{–}6\,\text{mm}$ wear layer; can be sanded limited times.

• Bamboo flooring

  • Rapidly renewable but brittle; PVC imitation planks eroding market share.

Decorative Laminates & Surface Composites

• Plastic laminates (Formica vs melamine)

  • Formica: thick HPL + phenolic craft-paper core → durable.

  • Melamine: thin LPL; cheap furniture & vertical surfaces.

  • Both vulnerable at edges; non-biodegradable, high embodied energy.

Protective & Aesthetic Finishes

• Prefer low-VOC: natural waxes, oils, modern water-borne polyurethanes.

  • Easy re-coat, lower toxicity, comparable lifespan.

• Avoid high-solvent polys/epoxies where possible (off-gassing).

Practical / Ethical Implications

• Specify FSC or equivalent + Good Wood Guide compliance for reduced environmental impact.

• Consider end-of-life: biodegradability (solid wood) vs landfill (plastics, melamine).

• Match fixings to treatment/chemistry (e.g.

  • Stainless for Accoya, CCA-treated pine contact zones).

Numerical / Standard References

• NZS3601 (timber sizes); NZS3640 (treatment levels).

• Typical framing sizes: $50\times100$ (rough), $45\times90\,\text{mm}$ (dressed).

• Treatment exposure categories $H1\text{–}H5$; stress grades $F1\text{–}F11$.