Defects in timber || Introduction || Classification

 Defect in timber

When a good Timber is subjected to any defect it losses following property. 

1. Colour 
2. Strength  
3. Decay  
4. Sound and 
5. Smell 

Defect in Timber is divided into five types 

1. Defect due to conversion 
2. Defect due to insect 
3. Defect due to fungi 
4. Defect due to natural forces 
5. Defect due to seasoning 

1. Defect in timber due to conversion 

This defect is caused when it is converted into different commercial shape and sizes. 

There are following types :-

A. Cheap stain 

This defect is indicated by signed or mark on finished surface of timber which is formed due to planning machine. Chip mark in timber 

B. Torn stain 

This defect is formed due to falling of instrument on timber during finishing. This defect is indicated by a small depression on finished surface of timber.

C. Diagonal stain 

This effect is formed due to improper sawing in timber. It is indicated by a diagonal mark on straight ground surface. 

D. Wane 

This defect is indicated by rounded mark on the finished surface of timber. In this defect original bark of timber is present on finished surface. 

2. Defect in timber due to insects 

This defect is mainly caused due to eating up to by insects. There are following types of defect due to in insects 

A. Beetles/Borers 

They form fine hole of diameter 2 mm in size. Conversion of timber into powder like substance without affecting top surface of timber. All types of timber get affected by Beatles. 

B. Marine borers 

They are found in is salty water. They form tunnel of size 25 mm in diameter and 60 mm in length. The timber which is affected by marine borers losses its strength and colour. There is no any timber which has completely immune from attack of marine borers. 

C. Termites 

These insects are also called as a white ant. It always lives in colony, and very fast in eating away the wood. Makes tunnel in different directions, and usually not disturb outer layer of timber. Few timber like teak, sal, etc. can resist the action of termite. 

3. Defects in timber due to fungi 

There are following types

A. Blue stain 

The sap wood of timber is stained to bluish colour by the action of certain fungi called as blue stain. It causes loss in appearance of wood. 

B. White rot 

This effect is mainly occurs due to the attack of fungi on the cellulose of timber convert it into white colour. 

C. Brown rot 

The brown rot  is used to indicate decay of timber thus the fungi of certain types attack on cellulose of brown colour. 

D. Heart rot  

It is the type of defect in which certain type of fungi attacks on the heart wood of timber is called as heart rot. 

E. Wet rot 

Some fungi cause chemical deposition on timber which converts into powder form. The alternate wet and dry condition favors the development of fungi which ultimately causes wet rot. To prevent the wet rot  we can use well seasoned wood or by painting Timber with Coal Tar. 

F. Dry rot 

Some types of fungi feed on wood and during feeding it converts it into dry powder form called as dry rot. Dry rot  occurs when proper ventilation & no free circulation of air is found. When a part of tree is seriously affected by dry rot, the damage portion may be completely removed and remaining portions should be painted with cuso4. 

4. Defect in timber due to natural forces 

A. Burls  

These are formed when a tree is subjected to injury or shocks in its young age. Due to sock irregular projection appears on the surface of timber. This defect is called as burls. It is also known as excrescences. Burls defects in timber 

B. Chemical stain 

Some trees causes to excrete the chemical and these chemicals ultimately cause stain on the surface of timber is called as chemical stain. Due to chemical stain the appearance of timber may get affected. What are natural defects in timber 

C. Knots 

This defect is mainly caused due to cut off branches of tree. The portion from which branch is removed receive nourishment from the adjacent stem for long time, and it ultimately results in formation of dark ring called as knots. It is hard and tough.Types of knots in timber 

D. Rind Gall 

Rind Gall is made up of two words. The first word is rind which means bark and the second word is gall which means abnormal growth. In this defect, a projection is formed on the stem of timber due to improper cutting of branches of tree called as rind gall. 

It is rarely found in trees. The part of the timber that is in it is very weak and not durable. And different parts of that timber have different strengths.

E. Druxiness 

It is indicated by white decay spot or stain on the surface of timber is called as druxiness. 

F. Foxiness 

It is indicated by red or yellow colour around the pith towards the outer layer. It generally happens to improper ventilation. 

G. Shake  

Actually shakes made in timber are cracks which cause high heat, wind, frost at the time of growth of the tree. It is that crack which separate the fibers of wood completely and partially.

It is following types of shakes depending upon their shapes and positions. 

Cup shape 

•   It is circular crack which not whole ring of timber. 

Heart shake  

•   It is crack which extended from centre cross section or Pith towards the outer surface of timber is called as heart shake. 

Ring shake 

•   It is a type of cup shape which covers whole circular ring. 

Star shake 

•   It is a crack which extends from outer edge towards the shape wood. 

Radial shake 

•   It is type of star which is generally find cracks. 

5. Defect in timber due to seasoning 

Seasoning is the process of removal of moisture from the timber by providing proper ventilation. The moisture content of seasoning wood about 10 to 12% of it dry weight. 

There are following types of seasoning defects 

A. Bow 

The curvature formed along the length wise direction this defect is called as bow. 

B. Cup 

The curvature formed along the width wise direction this defect is called as cup. 

C. Check 

Check is a kind of crack that separates fibers, but it does not extend from end to another. 

D. Split 

The defect in which cracks formed from one end to other end is called split. 

E. Twist 

These type of defects are formed by twisting of timber during seasoning. 

F. Honey combing 

Stress is developed in the heart wood during the drying process or seasoning for these stresses, cracks, etc. are created in the form of honey combing texture.Defects in timber