Defects in timber
Causes of timber defects
Causes of timber defects are divided into the following classes.
- Defects due to conversion and seasoning
- Defects due to fungi
- Defects due to insects
- Defects due to natural forces
Defects due to conversion
The following defects can occur during the process of converting timber to commercial form.
Chip mark: This is indicated by a mark or sign placed by chips on finished surface of timber.
Diagonal grain: Generally, this is occurred due to improper sawing of timber and it is indicated as diagonal mark on surface of timber.
Torn grain: Small impression is created because of falling of a tool or so.
Wane: Presence of original rounded surface on the manufactured piece of timber.
Defects due to fungi
As the name indicate the attack of timber by fungi when moisture content of timber is more than 20% and presence of air and warmth for the growth of fungi the following defects are caused
Blue stain: Sap of wood is stained to bluesh colour.
Brown rot: Decay or disease of timber by removal of cellulose compounds from wood and wood assumes the brown colour.
Dry rot: Convert the wood into dry powder form.
Heart rot: This is formed whenever branch has come out of a tree and the tree becomes weak and gives out hallow sound when struck with a hammer.
Sap stain: The sap wood looses its colour because of feed on cell contents of sap wood.
Wet rot: Caused due to chemical decomposition of wood of the timber and timber converts to grayish brown powder known as wet rot.
White rot: Attack lignin of wood and wood assumes the appearance of white mass.
Defects due to insects
Beetles: Small insects create larger holes around 2 mm in diameter and strike sap wood of all hardwood species. Tunnels are formed in all directions in sapwood by the larvae of these beetles and converted into fine flour like powder. They do not disturb outer cover and looks sound.
Marine borers: These make holes or bore tunnels in wood for taking shelter. The wood attacked by marine borers losing colour and strength.
Termites: White ants are very fast in eating(feed) away the wood from the core of the cross section. They make tunnels inside in different directions and normally do not disturb the outer shell or cover.
Defects due to natural forces
The main natural forces are responsible for causing defects in timber are abnormal growth and rapture of tissues
Burls: Irregular projections appear on the body of timber because of shock at younger age.
Callus: A soft tissue which covers the wound of tree.
Chemical stain: The chemical activity triggered discoloration.
Coarse grain: Annual rings are widened; tree grows quickly and thus timber has less strength.
Dead wood: Wood harvested from standing dead trees.
Druxiness: White decayed spots by fungi.
Foxiness: Due to poor ventilation during storage or by commencement of decay due to over maturity indicated in wood by red or yellow tinge.
Knots: Branch bases that are split, or cut off from the tree.
Rind galls: Rind means bark and gall is indicates abnormal growth and peculiar curved swellings found on the body of a tree.
Shakes: These are cracks which completely separate the fibres of wood.
Twisted fibres: As the name indicate its caused by twisting of young trees by fast blowing wind its also know as wandering hearts.
Upsets or ruptures: It shows wood fibers that are damaged by compression or crushing.