Defects in Wood | Wood Defects

Any unwanted features that deteriorate technical or commercial value are known as Defects. Defects are of two types: Natural and Non-Natura Defects.

Natural Defects in Wood

Natural Defects are the abnormalities observed due to the growth and environment of a living tree. The types of Natural defects are as follow:

  1. Defects in Wood | Wood Defects
    Defects in Wood
    Knots: A feature in which a branch embedded in the wood by the nature of growth.
  2. Shakes: It's a separation of fiber along the grain of a standing or freshly felled tree forming a crack.
  3. Cross Grain: It is the alignment of fibers and longitudinal elements deviated from direction parallel to the long axis of a piece of timber.
  4. Reaction wood: It's wood with more or less distinctive anatomical characteristics formed in parts of the learning tree and branches. Reaction wood of two types compression wood when abnormal wood is found in the underside of branches and leaning trunks and tension wood when abnormal wood is found in the upper side of leaning trunks and branches.
  5. Defects due to climber: When climbers hold trees tenaciously and not get broken by growing stem result in a groove on the bole of the pole; or occluded inside the stem and become permanent defect as they come out as loose knot while sawing.

Non-Natural Defects in Wood

Non-Natural Defects include those features either caused during treatment of felled timber or caused due to result from activities of external agents. 

The defects during treatment include caused during seasoning or during conversion and woodworking. Similarly, defects caused by external agents are either fungal defects or defects caused by insects.

The main seasoning defects are:

  1. Warping: Distortion in converted timber, a departure from its original plane as a result of seasoning. Types of Warping are:
    • Bowing: Curvature of the plane of the face such that it becomes concave or convex along the grain.
    • Cupping: Curvature of the plane of the face such that it becomes concave or convex across the grain.
    • Spring: It is a distortion in the longitudinal plane of the plank such that if laid on its tangential edge, it forms an arch.
    • Twist: A spiral distortion along the grain, manifested in a turning or winding of the feces of timber so that the four corners of any face are no longer in the same plane.
  2. Checks split and shakes: Rupturing of wood along the grain causes these defects. Check is the rupture of fibers forming a crack or fissure not extending through the piece from one face to the other. While split refers to the rupture of fibers forming a crack extending from face to face. Besides shake is a ring shake encircling the heart particularly called as 'round shake' and whose parts may be seen on the face or edge of converted timber is 'Shell shake'.
  3. Case-hardening, reverse case-hardening, and honey-combing: Case hardening refers to outer layers drying earlier than interior layers and results in tension across the grain. Reverse case-hardening refers to case-hardening but in reverse order i.e., in order to remove case-hardening timber gets over-steamed in that case outer layer permanently set in compression.
  4. Collapse: Collapse refers to a condition in which abnormal and irregular shrinking seen in certain very wet hardwoods on drying in kiln seasoning. 

Defects due to conversion and woodworking

  1. Boxed-heart
  2. Imperfect grain
  3. Machine burn
  4. Machine notches
  5. Machine gauge
  6. Miscut Timber
  7. Mis-matching
  8. Skip
  9. Wane

Fungal Defects in Timber

Defects in Timber caused by Insects and other animals

  1. Borers
    • Powder-post borers
    • Bark beetles
    • Flat-headed borers
    • Longhorn borers
    • Carpenter bees
  2. Termites
    • Termites are very destructive in nature for wood. The main food source of termites is cellulose thus consumed material that contains cellulose. There are two types of termite's dry wood termites and subterranean termites. 
  3. Marine borers
    • Crustaceans
    • Molluses: The larva of Molluses attached to submerged wood and bores holes and continues to enlarge burrow to suit rapidly growing size. There seem no signs of attack from outside but completely riddled with tunnels inside. Impregnation of wood with pure creosote under pressure helps to protect wood against these marine borers.
  4. Birds and Mammals
    • Wood-peckers damage standing wood making holes for their nest. Mammals like deer, bears, etc. damage bark and cambium causing shake. Elephants break branches and pull bark of standing trees causing wounds susceptible to fungal attacks.