Types of Defects in timber are grouped into the following divisions. The main natural forces responsible for causing defects in timber are abnormal growth and rapture of tissues.
1. Knots: Bases of branches or limbs which are broken or cut off from the tree as shown in the figure.
2. Star Shake: These are radial splits or cracks widest at the circumference and get diminishing towards the center of the tress. These may arise mostly from severe frost and fierce heat of sun.
3. Heart Shakes: These are the splits or cracks widest at the center and diminishing towards the outside circumference, this defects usually occurs in over matured tress and is probably caused due to the shrinkage of heart wood
4. Twisted fibers: caused by twisting of young trees by fast blowing wind as shown in figure.
5. Radial Shake: These are similar to star shakes but they are fine, irregular and numerous. They usually occur when tree is exposed to sun for seasoning after being felled down.
6. Rind galls: Rind means bark and gall indicates abnormal growth and peculiar curved swellings found on the body of a tree.