Timber Defects Knots A hard cross grain mass of wood that is formed in the trunk of a tree where a branch grows. Knots spoil the appearance and reduce the strength properties of wood. It also raises the seasoning defects and makes difficulties during wood working. Gum Pockets Cracks in the timber which contain gum. Shakes • A Shake is a partial or complete separation between the adjoining layers. • Maybe caused by growing stresses in the tree or by the impact of the tree with the ground during felling Cup Sahkes • Separation of wood fibres around the growth rings Heart Shake • A split which extends from the pith Felling Shake • Are fractures across the grain in which the fibres are broken transversely or are crushed by compression. • Various causes are suggested, such as felling across obstructions, and failure inside the growing tree caused by high winds. Cupping • A concave curvature across the face of a board. • Curvature is usually away from the centre of the tree. Spring • Curvature along the edge of the board. Bow • Curvature along the wide face of the board in the direction of the length. Twist • A spiral distortion along the length of a board. • Also known as wind. Wane • Edges or corners of sections of timber that encroach into the area of the bark. Splits & Checks • A split is a longitudinal crack which extends through the board, usually on the end • A check is a longitudinal crack that does not extend all the way through the board.