(i) Knots: Occur when a branch or limb is cut through during the process of conversion, knots reduce the strength of the timber owing to the short or gross grain which surrounds them. Types of knots include line or sound knot, loose or dead knot and spray knot.
(ii) Shakes: A shake is a partial or complete separation (splitting), between adjoining layer of wood, due to causes other than drying. They may be caused by the relief of growing stresses in the tree, or by the impact of the tree with
(iii) Interlocked Grain: This occurs when the fibres at adjacent layers in the growth ring are inclined at different angles to the axis of the timber. The layers are spiral in opposite direction about the axis of the tree.
(iv) Delay: This is the decomposition of the wood due to the action of wood destroying fungi which feed on the cell walls as well as the cell contacts. It is generally called not when the wood is in the more advanced states of decay.
(v) Working of wood: This is the alternation swelling and shrinking which occurs in seasoned changes when the humidity of the atmosphere fluctuates. The timber swells when the air becomes moist and shrinks when the air dries.
