Decay of Diseases Of Timber :
The Disintegration and turning to powder of timber Tissues is known as Decay or Disease of Timber. When the timber , without proper seasoning , Is placed in a position where there is no circulation of air, The disintegration of wood tissues is caused by fungi or other micro – organism. Dampness, alternate wet and dry conditions and old age accelerate decay of timber.
Classification of Diseases Of Timber :
1)Dry Rot :
The turning of timber tissues to almost a dry powder by fungi is called dry rot.There are many kind of fungi (means mushroom or any kind of spongy plant)which gain admittance into the Wood by means of pores, which breed in wood cells And spread minute thread like growth.
Favorable Condition of dry rots :
Sufficient temperature, Dampness , lack of free air and adequate food material.The fungus feed upon the wood and eats the wood Tissues, thus penetrating the wood fibers in all directions.
The wood is reduces to almost a dry powdery form by eating away the interior fibred of wood.The wood becomes soft like spongy mass usually grey in color.Sufficient temperature, Dampness , lack of free air and adequate food material.
Prevention of dry rots :
The timber which is well seasoned and free from sap, should be used because mostly sapwood is attacked by fungus.
It should be used at a place where there is free circulation and access of fresh air.
Remedy of dry rots:
The infected part of timber should be burnt or cut away & remaining portion should be painted with a solution of copper sulphate or with any other suitable preservative.
The wood cells which form the food of the fungi, should be impregnated with poison to control further growth of fungi.
The high temperature of seasoning kiln, will also Help In killing the fungi & expelling the moisture.
2) Wet Rots :
The disintegration of tissues of the timber due to alternate wetting & drying is called wet rot.Common found in a Living tree. The attack takes place through wounds in the bark by the access of water you can say high % of moisture.The decomposition of the effective part results in converting the wood fibers into a greyish brown powder.
Prevention of wet rots :
All timbers for exterior or underground work should be first properly seasoned and then coated with tar or some paint to keep out the dampness.
Remedy of wet rots :
for treating wet rot is by using a suitable preservative.
3) Insect Effect :
Such as termites (white ants), beetles, larva & marine borers cause decay of timber.They live in colonies. They build up mud tunnels to keep their movements covered & eating into the wood under the surface.
Prevention of wet rots :
The most effective way of controlling termites is To create damp proof conditions by using cement Concrete & cement mortar in joints so that termites may not work their way through the joints.
Well seasoned wood should be used and also protected from outside by sun & rain by a suitable cover to prevent it from insect attack.
Remedy :
The marine borers attack can be controlled by Providing copper bottom to wood which is to come in touch with water.
Causes of Decay Of Timber :
1)Presence of sap & moisture due to improper seasoning.
2) Stacking timber or using it in a position where there is no free circulation and access of fresh air.
3) Using timber at a place where it is subjected to alternate wetting and drying conditions.
4)Using Timer in structural work without the application of paint or any other suitable preservative on a seasoned wood, specially for underground work Such as fence post.
5) Applying protective coat of paint to unseasoned wood will induce decay by closing he outside pores.
6) Using timber where it is subjected to dampness.
Defects Of Timber :
1)Natural Defect developed during the growth of Tree
2) Defects occurring after a tree is felled.
Natural Defects :
1)Shakes : The partial or complete separations between adjoining layers of tissues are called shakes.
Shakes commonly formed in Log of trees which are allowed to stand even after they attain maturity and indicate old age.They lower the resistance to shear.
2) Heart Shakes :
The radial ruptures in annual rings or splits radiating from the heart of wood & extending towards the sapwood are called Heart Shakes & shake occurring at or near the pith and giving the appearance of a star on end of a timber log piece is called Star Shake.
These shakes are caused by quick drying of central part of the tree, having attained maturity. Felled tree nearing maturity.
3) Radial Shakes :
The radial splits which extend from the bark towards the pith are called Radial Shakes.These shakes are wider at outer ends and get narrower towards the pith. They are caused by shrinkage of outer tissues drying faster than the inner ones. Such defect usually arise during sudden seasoning of timber log and by excessive heat of the sun or server cold in forests.
4) Cup Shakes :
The opening along the growth rings are called cup shakes or ring shakes.
When the rupture of timber extends only a part round, it is called a cup shake and when whole way round, it is called a ring shake.
This defect is due to the sudden increase of moisture supplied by the roots of a tree and than quick drying.
B) Rindgall :
The curved swelling resulted from the growth of sap wood layers on wound, left by a falling branch or cut off branch in an irregular manner is called rindgall.
The new growth does not unite properly with the old wood and leaves a carity where decaying action may set in the form of rindgall.
C) Knots :
The dark hard pieces indicating places from where branches of a tree have been cut off or broken are called knots.
When the formation of knots if free from decay and such other defects and is firmly intact with the surrounding wood, it is called a live knot or sound knot.
A knot which is not held firmly in place is called a dead knot or loose knot.
Knots are source of weakness as they break the continuity of wood fibers.
A wood having a live knot can be used for engineering purpose.However, it is not safe to use a wood having dead knots.
Knots make the working of wood difficult.
Common knots are :
Round Knot, Oval Knot, Spike Knot, Grouped Knot & Pencil Knot.
D) Twisted Fibers :
The defect due to the fibers of tree which get twisted when young, by the force of wind is called Twisted FIBRES.
Twisted fiber make the wood weak & is only suitable for fuel purposes.Poles in unsawn condition where twisted fibers will give extra strength.
E) Upsets :
The defect caused by crushing or by injury in wood fibers are known as Upsets.
They occur usually during the growth of a tree.This makes the wood weak & unfit for any important work.
F)Burl, Burr or Excrescence :
The growth of a large excrescence bulge which is formed on the trunk or branch of a tree due to certain injury inflicted when the tree is young is called Burl, Burr or excrescence.
G)Coarse grains :
The widening of annual rings due to rapid growth of certain trees is called coarse grains.
The wood having coarse grains is weak in strength and durability.
Defects Occurring after the Tree Felled :
If the seasoning of the freshly felled logs of wood is not properly carried out, several defects creep in.
1)Case Hardening :
The different layers of wood are under stress. During Klin seasoning, the outer side of timber gets hard while the inner core remains still wet due to rapid surface drying. This type of defect is known as case hardening.
2) Honey Combing :
This defects is due to separation of the tissues in the interior of timber due to drying stresses, caused by incorrect kiln seasoning as the interior wood dries earlier than the external surface.
3) Collapse :
The defect is due to the corrugates appearance of timber , caused due to excessive and uneven shrinkage during drying.
4)Foxiness :
This defect is due to yellowish or reddish stains , caused by over-maturity and lack of ventilation during storage of timber.
5)Twisting & Bowing :
If the unevenly dried timbers are subsequently sawn into smaller sections , some of the stresses are released and defects such as twisting, cupping, bowing & splitting appear distinctly in them.
a)Twist : It means a spiral distortion.
b) Cup :
A curvature in a piece of timber across its width in known as Cup.
C)Bow :
A curvature in a piece of timber along the direction of its length.
D) End Split :
A split of end of a log or a piece of timber.
Requirement of Timber :
1)It should be easily & cheaply available.
2)It should allow coat of paints & polish etc.
3)It should be highly penetrative.
4)It should be permanent nature and not to be washed away by water or spoiled by heat, light etc.
5)It should be extremely poisonous, even in small doses, to fungi & insects.
6)It should be allow decorative treatment on timber after being applied over timber surface.
7) It should be non Inflammable.
8) It should after high resistance to the moisture & dampness.
9) It should not reduce the strength of the timber & should be non –corrosive to metal in contact.
10)It should not catch fire easily.
11)It should not give bad smell and not be injurious to workmen and animals.
Tanya Decor 