This is a process by which moisture content in a freshly cut tree is reduced to a suitable level. By doing so the durability of timber is increased.

Objectives of seasoning are

To decrease the weight and there by reduce the cost of transportation.

To maintain shape and size when used.

To improve resistance to decay.

To make timber safe against attack of fungi and insects.

To reduce the tendency of crack, shrinkage and warp.

To make timber is easily workable.

To allow burning radially when used as fuel.

The various methods of seasoning used may be classified into:

(i) Natural seasoning

(ii) Artificial seasoning

NATURAL SEASONINGWhen seasoning of timber is carried out by natural air , it is called natural

seasoning or air seasoning. Air seasoning is carried out in a shed with a platform.

Ground is levelled and a platform constructed 30 cm above ground level.

Care is taken to see that there is proper air

circulation around each timber balk. Over

a period, in a natural process moisture

content reduces. A well seasoned timber

contains only 15% moisture. This is a slow

but a good process of seasoning

Depending on climate, moisture content can

brought down to 10 to 20%.

Does not required skilled supervision.

This method is simple and economical.

Controlling the seasoning is difficult as natural air using for seasoning.

Drying of surfaces may not be even and uniform.

If the ends are not protected properly, chance of end splitting will be there.

Moisture content of wood may not be brought down to the required level.

The process is very slow and takes 2 to 4 years.

Space required for this process will be more.

ARTIFICIAL SEASONING

Artificial seasoning reduce many disadvantage of natural seasoning.

In this the moisture content can be brought down to required level,

duration for seasoning can be reduced, and surface drying will be even

and uniform.

Following method are used

Boiling: In this method timber is immersed in water and then water is

boiled for 3 to 4 hours. Then it is dried slowly. Instead of boiling water

hot steam may be circulated on timber. The process of seasoning is

fast, but costly.

water seasoning: Timber pieces are completely immersed in water

preferably in running water of a stream or river for 3 to 4 weeks.

During this period, sap contained in timber is washed away. It is taken

out and dried carefully with free access of air it is a faster method.

Kiln Seasoning: Kiln is an airtight chamber. Timber to be seasoned

is placed inside it. Then fully saturated air with a temperature

35°C to 38°C is forced in the kiln. The heat gradually reaches

inside timber. Then relative humidity is gradually reduced and

temperature is increased, and maintained till desired degree of

moisture content is achieved.

Electrical Seasoning: In this method high frequency

alternate electric current is passed through timber. The

resistance increases wood dries internally which result in

the production of heat.it is faster method, but cost and

maintains is high.

Chemical Seasoning: In this method,

the timber is immersed in a solution of

suitable salt. Then the timber is dried in

a kiln. It ensures uniform seasoning of

outer and inner parts of timber. Electrical Seasoning

It means protecting timber from attack fungi and insects so that its life is

increased. Timber is to be seasoned well before application of preservatives

Characteristics of a Good Preservative

It should be cheap.

It should be strongly toxic to insects and fungi.

It should be highly resistant to water and dampness.

It should not be soluble in water nor should it change in composition under

ordinary climatic condition.

It should be harmless to human beings.

It should be economical and available readily in large quantities.

It should be simple in application.

It should be stable.

It should be odourless and colourless.

ASCU Treatment : This preservative is developed by the Forest

Research Institute, Dehradun. It consists of 1 part of hydrated

arsenic pentoxide ,3 parts by weight of copper sulphate and 4 parts of

potassium dichromate. This preservative is available in powder form.

Chemical salt: These are the preservatives made by dissolving salts

in water. The salts used are copper sulphate, mercury chloride, zinc

chloride and sodium fluoride. After treating the timber with these

chemical salt paints and varnishes can be applied to get good

appearance.

Creosote: Creosote oil is obtained by distillation of coal tar. The

seasoned timber is kept in an air tight chamber and air is

pumped out from timber. Then creosote oil is pumped into the

chamber at a pressure of 7 to 10 Kg/cm at a temperature of

50°C. After 1 to 2 hours timber is taken out of the chamber.

Tar Treatment: Hot coal tar is applied to timber with brush.

The coating of tar protects the timber from the attack of fungi

and insects. It is a cheapest way of protecting timber.

Oil Paints: Two to three coats of oil paints are applied on clean

surface of wood. The paint protects the timber from moisture.

2

Brushing: Preservatives are applied to timber surface using

brushes. This is the simplest method and adopted for

seasoned timber. Several coating may be given for better

protection.

Charring: The surface to be charred is kept wet for about

half an hour and is burnt over wood fire for a depth of

15mm. The charred portion is cooled with water.

Spraying: Preservatives sprayed with pressure over timber

surface. It is superior to brushing and is quite effective.

Dipping & Steeping: Timber is dipped in preservatives for short

duration. Better penetration than spraying& brushing.

Steeping done for a few hours to days or weeks.

Injecting under pressure: in this method preservatives are

injected to timber under pressure. Effective method of

preservation.

Hot and Cold open tank treatment: Timber is submerged in a

tank with preservative solution heated to 85 C & 95 C for few

hours. then allowed to cool the tank, while the timber is

submerged in the tank.

0 0

DEFECTS IN TIMBER

Various defects which are likely to occur in timber may

be grouped into the following:

1) Defects due to natural forces

2) Defects sue to fungi

3) Defects due to insects

4) Defects due to conversion

5) Defects due to seasoning

CHEMICAL

STAIN

KNOTS

SHAKES

RIND

GALLS

UPSETS

BURLS

TWISTED

FIBRES

1. CHEMICAL STAIN:-THE WOOD IS SOMETIMES

DISCOLOURED BY THE CHEMICAL ACTION

CAUSED WITH IT BY SOME EXTERNAL

AGENCY.THIS IS KNOWN AS CHEMICAL STAIN.

2.RIND GALLS:-THE RIND MEANS BARK AND

GALL INDICATES ABNORMAL GROWTH.HENCE

CURVED SWELLING FOUND ON THE BODY OF

TREE ARE KNOWN AS RIND GALL.THEY DEVELOP

AT POINTS FROM WHERE BRANCHES

ARE IMPROPERLY CUT OFF OR REMOVED.THEY

ARE RARELY FOUND IN A TREE AND THE TIMBER

IN THIS PART IS VERY WEAK AND NOT DURABLE.

3.KNOTS:- KNOTS ARE ROOTS OF SMALL BRANCHES OF THE TREE.

THEY MAY BE LIVE OR DEAD. THEY BREAK THE CONTINUITY OF

FIBRES. SMALL KNOTS ARE NOT HARMFUL BUT TIMBER WITH

LARGE KNOTS OR A NUMBER OF KNOTS ARE INJECTED.

4.DEAD WOOD:-THE TIMBER WHICH IS OBTAINED FROM DEAD

STANDING TREES CONTAINS DEAD WOOD.IT IS INDICATED BY

LIGHT WEIGHT AND REDDISH COLOUR.

5.SHAKES:-SHAKES ARE CRACKS WHICH PARTLY OR COMPLETELY

SEPARATE FIBRES OF WOOD. ALSO THESE ARE LONGITUDINAL

SEPERATIONS IN WOOD BETWEEN THE ANNUAL RINGS.

HEART SHAKES:-THESE CRACKS OCCUR IN CENTRE OF CROSS-

SECTION OF TREE AND THEY EXTEND FROM PITH TO SAP WOOD IN

DIRECTION OF MEDULLARY RAYS.

STAR SHAKES:-THESE ARE CRACKS WHICH EXTEND FROM

BARK TOWARDS THE SAP WOOD.

CUP SHAKES:-IT APPEARS AS CURVED SPLIT WHICH PARTLY OR

COMPLETELY SEPERATES ANNUAL RINGS FROM ONE

ANOTHER.IT IS CAUSED DUE TO UNEQUAL GROWTH.

RING SHAKES:-WHEN CUP SHAKES COVER THE ENTIRE RING,THEY

ARE KNOWN AS RING SHAKES

RADIAL SHAKES: THEY ARE SIMILAR TO STAR

SHAKES.BUT THEY ARE IRREGULAR,FINE AND

NUMEROUS.

6.TWISTED FIBRES:-THESE IS CAUSED BY PREVALENT WIND TWISTING OF

YOUNG TREE CONSTANLY IN ONE DIRECTION

7.UPSETS:-THESE INDICATE WOOD FIBRES WHICH ARE INJURED BY

CRUSHING OR COMPRESSION

8.BURLS:-THEY ARE PARTICULARLY FORMED WHEN A TREE

RECIEVES SHOCK OR INJURY IN ITS YOUNG AGE.DUE TO ITS

INJURY,THE GROWTH OF TREE IS COMPLETELY UPSET AND

IRREGULAR PROJECTIONS APPEAR ON THE BODY OF TIMBER

9.CORSE GRAIN:-IF THE TREE GROWS RAPIDLY,THE ANNUAL RINGS ARE WIDENED.IT

IS KNOWN AS THE CORSED GRAIN TIMBER AND SUCH TIMBER POSSESSES LESS

STRENGTH.

10.DRUXINESS:-IT IS AN EARLY DECAY WHICH APPEARS AS WHITISH SPOTS , CONCEALED BY

HEALTHY WOOD. .

BLUE

STAIN

BROWN

ROT

DRY

ROT

HEART

ROTWET

ROTWHITE

ROT

BLUE STAIN :-THE SAP OF WOOD IS STAINED TO BLUISH

COLOUR BY THE ACTION OF CERTAIN TYPE OF FUNGI

BROWN ROT :-THE TERM ROT IS USED TO INDICATE

DECAY OR DISEASE OF TIMBER. SOME TYPE OF FUNGI

REMOVES CELLULOSE COMPOUNDS FROM WOOD AND

WOOD TURNS BROWN COLOUR

WHITE ROT:-IT IS JUST OPPOSITE OF BROWN ROT.IN THIS

CERTAIN TYPE OF FUNGI ATTACK WOOD AND WOOD ASSUMES

THE APPEARANCE OF A WHITE MASS

HEART ROT:-THIS IS FORMED WHEN BRANCH HAS

COME OUT OF THE TREE, FUNGI ATTACK THE HEART

WOOD AND THIS MAKES TIMBER WEAK.

WET ROT:-CERTAIN FUNGI CAUSE CHEMICAL

DECOMPOSITION OF WOOD OF TIMBER AND

CONVERT TIMBER INTO GREYISH BROWN POWDER

DRY ROT :- SOME FUNGI FEED ON WOOD AND DURING

FEEDING THEY CONVERT WOOD INTO DRY POWDER .THIS IS

KNOWN AS DRY ROT

CAUSED BY

BEETLES MARINE

BOARERS

TERMITES

Flour like powder

BEETIES ARE SMALL INSECTS WHICH MAKES

ABOUT 2mm DIAMETER PIN HOLES. THE TIMBER

MAY BE CONVERTED INTO FINE FLOUR LIKE

POWDER.

BOARS

MARINE BORERS ARE GENERALLY FOUND IN SALTY

WATER. THEY MAKES HOLES IN WOOD FOR MAKING

SHELTER. THE HOLES MAY BE AS LARGE AS 25mm IN

DIAMETER AND 60mm LONG

TERMITES ARE KNOWN AS WHITE ANT. THEY EAT THE WOOD

VERY FAST AND MAKE TUNNELS INSIDE THE TIMBER IN

DIFFERERNT DIRECTIONS AND USUALLY DO NOT DISTURB THE

OUTER SHELL. HENCE TIMBER PIECES ATTACKED BY

TERMITES APPEAR TO BE STRONG FROM OUT SIDE TILL IT

COMPETELY FAILS.

CHIP MARK DIAGONAL GRAIN TORN GRAIN

CHIP MARK:-THIS DEFECT IS INDICATED BY MARK

PLACED ON FINISHED SURFACE OF TIMBER.

DIAGONAL GRAIN:-THE DEFECT IS FORMED DUE TO

IMPROPER SAWING ANS IS INDICATED BY DIAGONAL

MARKS ON STRAIGHT GRAINED SURFACE OF TIMBER

TORN GRAIN:-DEFECT CAUSED WHEN A SMALL

DEPRESSION IS FORMED ON A FINISHED SURFACE OF

TIMBER BY FALLING A TOOL OR SO

TORN

GRAIN

BOW:-THIS DEFECT IS INDICATED BY CURVATURE FORMED

IN DIRECTION OF LENGTH OF TIMBER

CUP:-THIS DEFECT IS INDICATED BY CURVATURE FORMED

IN TRANSVERSE DIRECTION OF TIMBER

TWIST:-WHEN A PIECE OF TIMBER HAS SPIRALLY

DISTORTED ALONG ITS LENGTH,IT IS KNOWN AS A TWIST

CHECK:-A CRACK WHICH SEPERATES FIBRES OF

WOOD.IT DOES NOT EXTEND FROM ONE END TO

THE OTHER

SPLIT:-WHEN CHECK EXTENDS FROM ONE END

TO OTHER,IT IS KNOWN AS A SPLIT

RADIAL SHAKES :-THESE SHAKES ARE RUN IN THE

RADIAL DIRECTION.

COLLAPSE:-COLLAPSE OF WOOD DUE TO UNEVEN

SHRINKAGE DURING DRYING.

DECAY OF TIMBER

When timber loses its value as an engineering material, it is said to be

decayed. The decayed timber cannot be used for engineering purposes.

Following are considered as the causes of decay of timber.

Bad storage.

Alternate wetting and drying.

Presence of insects.

Keeping timber in contact with damp wall and damp floor.

Improper seasoning.

Use of timber without removing sap wood.

Presence of fungi.

Shocks or injuries received during young age.

Use of unseasoned timber with application of protective coat of paint or tar.

Use seasonal timber without the application of preservatives.

REFERENCE BASIC CIVIL ENGINNERING = MA COLLEGE

BASIC CIVIL ENGINNERING=SHIBU NALPAT

GOOGLE= WWW.CIVILENGINEERINGX.COM

GOOGLE= WWW.SLIDESHAREE.NET

SUBMITTED TO,HELEN THOMASASST.PROFESSORCIVIL ENGINEERINGMITS

GROUP MEMBERS,

13. ARUN .C.S

14. ASHITHA SHAJI

15. ATHUL STANLY

16. BINCY BABU