Wood Properties and Classification Explained

Wood Properties and Characteristics

Physical Properties of Wood

• Anisotropy: Wood exhibits different physical and mechanical properties depending on the direction relative to the grain.
  • Axial: Parallel to the tree's growth.
  • Radial: Perpendicular to the axis.
  • Tangential: Perpendicular to the other two.
• Structure: Conifers typically have a homogeneous structure.
• Density: Mass at 0% moisture is termed anhydrous basis; mass at 12% moisture is termed normal mass.
• Other properties include color, brightness, texture, toxicity, and hygroscopicity.
• When wood has a moisture content higher than its environment, it loses water, leading to shrinkage and potential losses.

Mechanical Properties of Wood

• Compressive Strength: Highest when force is applied parallel to the fibers.
• Tensile Strength: Maximum when force acts parallel to the fibers.
• Flexural Strength: Maximum when force acts perpendicular to the fibers (causing bending).
• Shear Strength: The ability of wood to resist forces causing one part of the material to slide over an adjacent part.

Wood Classification

Types of Wood

• Resinous Wood (Softwoods): Often used in construction.
  • Pine: Good strength, durability, and elasticity.
  • Fir: Low resin content and elastic.
  • Larch: Fine-grained, very workable, resulting in a smooth, shiny finish.
• Hardwood: Classified into various types.

  • Common Hardwoods

    • Oak: Very strong and stable.
    • Encina (Holm Oak): Resistant to moisture and temperature changes.
    • Olmo (Elm): Hard, elastic, and waterproof.
    • Hague (Beech): Soft when cut, becomes hard and heavy.
    • Fresno (Ash): Flexible, bendable, resilient, and tough.
    • Eucalyptus
    • Banana

  • Fruitwood / Nutwood

    • Walnut: Compact and easy to work.
    • Cerezo (Cherry)
    • Apple
    • Olive

  • African Hardwoods

    • Abelay: Sparse grain.
    • Bokapi: Very dense and resistant.
    • Mber
    • Sapelli

  • Exotic and Precious Woods

    • Mahogany: Very elastic, stable, and easy to work.
    • Ebony: Rigid, durable, and low hygroscopicity.
    • Rosewood
    • Teka (Teak): Resistant to fungi and insects.

Industrial Wood Boards

• Plywood: Made from thin wood veneers layered with fibers oriented orthogonally, bonded with strong glues (like casein) and pressed. Always has an odd number of layers.
• Conglomerate (Particleboard/Fiberboard): Can be made from chips or fibers.
• Mineralized Conglomerate: Obtained from straw, leaves, chips, etc., mixed with cement pastes or mortars. Used in masonry and concrete structures, not typically woodworking.
• Armed Board (Blockboard/Laminboard): Made from strips (laths) or straw coated with veneers, strongly glued and pressed. Used in prefabrication of door leaves and furniture panels.