1. TIMBER

2. Introduction Oldest material used in construction
Timber, word derived from timbrian which means to build.
Denotes wood suitable for building works or engineering purposes.
Different terms
Converted timber-sawn and cut into suitable sizes
Rough timber-obtained after felling a tree
Standing timber-timber contained in a living tree

3. Properties of timber
Amenability to mechanical working
Small bulk density
High strength
Drawbacks of timber as engineering material
Susceptibility to decay
Fluctuations in properties due to change in moisture
content
Variations in strength in length and across fibre

4. CLASSIFICATION OF TREES
Exogenous Trees : Conifers & Deciduous
increase in bulk by growing outward
distinct consecutive rings – annular rings
most suitable for engineering purpose
eg. Teak, deodar, sal
Endogenous Trees
grows inwards
fiborous mass is in their longitudinal section
very limited engineering application
eg. Bamboo, cane, palm

6. STRUCTURE OF A TREE Consist of three parts : trunk, crown, roots
Trunk : to support the crown and to supply nutrients from roots to leaves
Roots: to implant the trees in the soil
Macrostructure: Structure of wood visible to naked eye or at small magnification
Microstructure: Structure of wood visible at great magnification

7. CROSS SECTION OF AN
EXOGENOUS TREE

9. Pith
innermost central portion
core of the tree
consist of cellular tissues
nourishes the plant in young age
Heart Wood
inner annular rings surrounding the pith
dark in colour
imparts rigidity to the tree
provides strong, compact and durable timber for
engineering purposes
Sap Wood
outer annual rings between heart wood and cambium layer
light in colour
indicate recent growth, contains sap
active part in growth of tree

10. Cambium layer
thin layer of sap between sapwood and inner bark
sap not been converted into sap wood
Inner Bark
inner skin which covers cambium layer
give protection to cambium layer
Outer Bark
outer skin of tree
dry and dead layer which prevents from external weathering
Medullary rays
thin radial fibers extending from pith to cambium layer
hold together the annular rings of heart wood and sap wood

11. BAMBOO

12. VARIETIES OF TIMBER

13. BAMBOO

14. BANYAN

15. SIMUL

16. BIJASAL (VENTEAK)

17. COCONUT

18. TAMARIND

19. HOPEA

20. SEASONING OF TIMBER
Fresh timber – contains 50% of dry weight as water – has to be dried
The process of drying timber is known as seasoning of timber – getting rid of sap wood and moisture content
Timber becomes lighter and less bulky
Strength get increased
Seasoning – controlled conditions – uniform rate
Irregular seasoning – shrinkage

21. OBJECTIVES OF SEASONING OF TIMBER
To impart hardness, stiffness, strength.
To make timber safe from fungi, insects.
To make timber easily workable.
To decrease the weight of timber.
To maintain shape and size when used.
To make timber suitable for receiving paints, varnishes etc.
To reduce tendency to crack, shrink and warp

22. METHODS OF SEASONING Natural seasoning / Air seasoning
Artificial seasoning

23. Natural seasoning Timber is cut into suitable sections of planks.
A platform is constructed 30 cm above GL.
Timber stacked horizontally or vertically.
The layers are separated by dry pieces of wood (spacers) of thickness 25 mm to 35 mm. Spacers may be kept at mm.
The stack is protected from rain & sunlight.

24. Natural seasoning

26. Advantages of natural seasoning
Does not required any skilled supervision.
Moisture content of wood can be brought down to about %.
Economical.
Cheap and simple.

27. Disadvantages Less control over air. Non uniform drying
Fungi and insects attack during seasoning.
Time consuming

28. Artificial seasoning Water seasoning Boiling Electrical seasoning
Chemical seasoning
Kiln seasoning

29. Water seasoning
Logs of wood are immersed in running water of stream for 2-4 weeks and dried in open air.

30. Boiling
Timber is boiled in water for 3-4 hours, taken out and dried slowly.
Period of seasoning is less
More expensive.
Less strength.

31. Electrical seasoning
Passing high frequency AC through the timber. The timber gets heated and dries out.
Results in uniform seasoning
Very rapid method
Capital cost of equipment is more

32. Chemical seasoning
Green timber is soaked in saturated solution of suitable salt then removed and seasoned.
Interior surface of timber dries in advance of exterior
Less chance of external cracks.

33. Kiln seasoning
Drying of timber is carried out inside an airtight chamber or oven.
Heated air of temp 35-38oC is forced inside the chamber.
Temperature maintained till a desired degree of moisture content is attained.

34. Preservation of timber
The main principle in preservation of timber is application of a suitable preservative on the surface of the timber
Commonly used preservatives are oil paints, coal tar, creosote oil, solignum paints, ascu and chemical salts
Objectives of Preservation of timber
1. to increase the life of timber structures
2. to make timber structure durable
3. to protect timber from attack of fungi, insects etc. .

35. REQUIREMENTS OF GOOD PRESERVATIVES
Capable of covering large area with small quantity
Cheap and easily available
Durable, not affected by heat, light etc.
Free from unpleasant smell
Non – inflammable
Efficient in killing fungi, insects etc.
Safe and harmless for persons and animals
Not affect strength characteristics of timber
High resistance to moisture and dampness

36. Methods of preservation
Brushing
Charring
Dipping and steeping
Hot and cold open tank treatment
Injecting under pressure
Spraying
Fire proofing of timber

37. Brushing
Preservative solution applied over timber using good quality brushes
Simplest form, adopted for seasoned timber
Pre-requisite : cracks should be filled up before brushing
Several coats of preservative may be applied at proper intervals to ensure efficient absorption of preservatives

38. Charring
Adopted for lower ends of timber posts before embedding in ground
Kept wet for ½ an hour
Burnt over fire (15 mm deep) – layer of coal is formed
Cooled with water

39. Dipping and steeping
Timber soaked or dipped in a solution of preservative for a short period ( few hours to days to week)
Ensures better penetration of preservatives

40. Hot and cold open tank treatment
Timber is submerged in a tank of preservative solution for few hours at 850 – 950 C
Tank is then allowed to cool down gradually with the timber still soaked inside the tank
Effective in giving protection to sap wood

41. Injecting under pressure
Preservative is injected into the timber
Mainly adopted in creosoting
Most effective method of preserving timber
Requires special treatment plant
Specially suited for treating non durable timber (prone to attack of fungi and insects)

42. Spraying
Preservative is filled in spraying pistol and is then applied on timber surface under pressure
Pistol works under compressed air
Effective and superior than brushing

43. Types of preservatives
Ascu
Chemical salt treatment : Zncl, NaF etc…
Coal tar
Creosote oil
Oil paints
Solignum paints

44. Ascu treatment Ascu – developed by Forest Research Institute, Dehradun
Ascu – mixture of hydrated arsenic pentoxide, copper sulphate and potassium or sodium dichromate in 1:3:4 proportion
Ascu – available in powder form
6 parts of ascu is mixed in 100 parts of water to form a solution
Spray the solution on the timber surface

45. Chemical salts treatment
Solution of different salts are prepared and is then applied on timber surface
Zinc chloride
Sodium fluoride
Magnesium silico – fluoride
Copper sulphate
Odourless and non inflammable

46. Coal tar
Timber - coated with hot coal tar with the help of a brush ( coal tar becomes workable when heated)
Process is called as tarring
Unpleasant smell and appearance
Makes timber unsuitable for painting but makes it fire resistant

47. Creosoting Creosote oil – dark brown liquid
Obtained by distillation of tar
Well seasoned timber dried for 24 hrs
Kept in airtight chamber and air removed
Creosote oil pumped at 7 to 10 kg/cm2 at 50°C till full saturation at 480 C

48. Oil paints Coated with 2-3 coats of oil paint
Pre-requisite : timber should be well seasoned or else the sap would get confined and causes decay
Makes it durable

49. Solignum paints
Preserve the timber from white ants, as they are highly toxic in nature; lead free glossy paints
Can be mixed with colour pigments and can be applied on timber in hot state with the help of a brush
Timber surface may be given desired colour and appearance