Wood Defects, Diseases, and Preservation Strategies

Wood Diseases: Defects, Alterations, and Protection

Understanding Wood Defects

Wood can exhibit various issues that impact its quality and structural integrity. These can be broadly categorized into problems, defects, and alterations.

Common Wood Defects

• Problems: Knots, heart offset, and similar issues that occur during the tree's growth period.
• Defects: Modify the structural order, such as bark inclusions and double sapwood.
• Alterations: Include cracks, decay, and other forms of damage.

Qualities of Good Wood

A high-quality piece of wood typically possesses the following characteristics:

• Straight grain
• Regularity in the annual rings
• Fresh smell
• Absence of cracks
• Shiny and smooth surface when ripped

Specific Wood Defects Explained

• Knots: A localized anomaly in the wood structure, produced by a branch becoming subsumed as the tree grows. Knots are defects that alter the direction of wood fibers, significantly influencing wood strength.
• Heart Eccentricity: Occurs when the central axis of the trunk deviates substantially from symmetry.
• Interlocked Grain: The wood surface appears torn and becomes difficult to work.
• Twisted Grain: The wood fibers are arranged in a helical pattern.
• Lupi (Burls): An outgrowth on the trunk with a globose and smooth surface, composed of irregularly interlocking wood fibers.
• Warts: A woody extrusion of different origin, resulting in an alteration of the wood structure.
• Irregularities in Ring Width: Caused by factors such as frost, lack of air, or excessive sun exposure.
• Bark Inclusions (Entrecorteza/Entrecasco): A possible source of infection within the wood.

Heartwood Defects

• Open Heart: Wide radial cracks that start from the core of the wood.
• Star Shake (To de Gallo): Cracks directed from the pith to the periphery, often accompanied by a bad smell, indicating the beginning of wood rot.

Other Internal Wood Issues

• Internal Sapwood Decay (Entrealbura): Localized death of an area within the outer layers of a tree. This area can begin to rot, affecting the entire piece.
• Excess Sapwood: An excess of sapwood, resulting from slower than normal lignification.
• Ring Shakes (Colan): A lack of adhesion between annual rings within the tree.
• Resin Pockets (Resin Bags): An elongated cavity within the timber containing resin. These are not visible during sawing.

External Wood Cracks and Damage

• Checks (Fender): Longitudinal cracks caused by several reasons:
  • Frost Checks: Caused by extreme cold.
  • Drying Checks: Due to shrinkage caused by drying.
  • Felling Checks: Caused by tearing of woody elements during felling.
• Heart Hole from Felling (Apeo): Occurs when felling the tree, leaving a sliver of the central part of the log attached to the stump.

Wood Alterations: Biotic and Abiotic Causes

Biotic Factors Affecting Wood

Biological agents can significantly damage wood, leading to its destruction.

• Fungal Destruction: When moisture content and temperature are suitable, fungi develop and destroy wood by consuming its components.
• Insect Attack on Wood: Characterized by holes or galleries produced by insects in wood exposed to air or in contact with the ground.
  • Termites:
    • Subterranean Termites: Live in large soil colonies. Their primary nest is outside the wood, but they build secondary nests and galleries into the wood.
    • Drywood Termites: Can destroy a structure unnoticed from the exterior, as they leave a thin surface layer (1-2 cm thick).
  • Woodworm: Drills circular galleries with a diameter of 1 or 2 mm.
• Destruction by Marine Organisms:
  • Molluscs
  • Crustaceans

Abiotic Causes of Wood Damage

Non-biological factors can also lead to wood degradation.

• Fire: Incomplete combustion occurs without sufficient oxygen, leading to charring and structural weakening.
• Weathering: Changes in humidity lead to volumetric changes (swelling and shrinking), causing cracks and surface degradation.
• Chemicals: Acids and bases can attack wood by hydrolyzing or dissolving cellulose and lignin, leading to structural breakdown.

Methods for Wood Protection

Protecting wood from defects and alterations is crucial for its longevity and performance.

Wood Preservation Techniques

• Drying
• Artificial Seasoning
• Surface Treatments:
  • Carbonization
  • Painting
  • Immersion
  • Pressure Treatment (Autoclave)