Project Report on Timber

An exclusive project report on Timber. This project report will help you to learn about: 1. Meaning of Timber 2. Qualities of Good Timber 3. Water Absorption 4. Causes 5. Fire Resistance and Fire-Proofing 6. Preservation 7. Seasoning 8. Different Uses 9. Structural Properties 10. Substitutes for Normally Used Timber 11. Timber as Construction Material.

Contents:

1. Project Report on the Meaning of Timber
2. Project Report on the Qualities of Good Timber
3. Project Report on the Water Absorption of Timber
4. Project Report on the Causes of Decay/Deterioration of Timber
5. Project Report on the Fire Resistance and Fire-Proofing of Timber
6. Project Report on the Preservation of Timber
7. Project Report on the Seasoning of Timber
8. Project Report on the Different Uses of Timber
9. Project Report on the Structural Properties of Timber
10. Project Report on Substitutes for Normally Used Timber
11. Project Report on Timber as Construction Material

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Project Report # 1. Meaning of Timber:

Timber is an important material in building construction. It is used in various ways as component parts of building e.g., beams, joists, door and window frames and shutters, partition walls, etc. It is used in making temporary supporting structures required during construction. Timber or wood used in construction are basically of two varieties — soft wood and hard wood.

Soft woods form a group of evergreen trees. Hard woods form of a group of broad-leaf trees. It is to be noted that the terms soft woods and hard woods have commercial importance only. It is quite likely that some variety of soft wood may prove to be stronger than some variety of hard wood.

Timber is a natural product. It is basically organic in nature and not inert to atmospheric effects. It, therefore, undergoes deterioration or decay commensurating with its age, decay conditions, loading, change of its properties, etc. due to which timber cannot be used universally in all places, but are mostly for indoor works and require protective measures when used in outdoor works.

Besides, scarcity of timber has also resulted in the increase in its cost, All these have led to alternative substitutions, which in most cases is reinforced concrete, steel, aluminium, glass, asbestos or industrial timber.

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Project Report # 2. Qualities of Good Timber:

Some of the qualities of good timber are:

a. Appearance:

When a good quality timber is cut with a saw, the woody fibres should not present a woolly appearance or clog the saw; but should appear firm, hard and shining. Narrowness of the annual rings indicates slower growth and would be more durable. The cellular tissue of the medullary should be hard and compact.

b. Colour:

The colour of the cut surface should preferably be dark. Light colour usually indicates timber of low strength.

c. Defects:

It should be free from all sorts of defects e.g., knots, flaws, shakes, fungi infections, sap stain, etc.

d. Durability:

It should be durable and should be able to resist the actions of fungi infections. It should have high degree of elasticity, fibres should be straight, should be hard, have good

resistance to fire, should not deteriorate easily under wear or abrasion, should give clear ringing sound, should be sufficiently strong, tough and uniform in structure, have low rate of permeability, should be capable of retaining shape, and emit its characteristic odour, should be able to stand reasonably the weathering effects, and should be heavy.

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Project Report # 3. Water Absorption of Timber:

Timber is susceptible to moisture absorption. When in contact with water or under conditions of high humidity it swells and again it shrinks when kept in dry atmosphere. Apart from swelling and shrinking of timber, which are the main effects, distortion takes place as the degree of absorption is not uniform.

Due to swelling and shrinking internal stresses develop splitting and disintegrating the timber under extreme conditions. Timber, therefore, requires protective coats over the surface to resist the ingress of moisture.

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Project Report # 4. Causes of Decay/Deterioration of Timber:

Timber in use deteriorates due to various reasons.

The main causes of deterioration are:

i. Mechanical wears of timber:

This naturally depends upon the surface hardness of the timber and the extent to which it is exposed to driven sand or other abrasive agents. In general, such wear is of little practical importance.

ii. Chemical action:

Timber has good chemical resistance; however, strong acids and bases may cause decomposition of timber and thereby initiate disintegration of the structure. If timber is kept in contact of such material, it must be suitably protected by plastic cladding or cladding with chemically inactive material.

iii. Weathering:

Weather is the main agent causing alternate shrinkage and swelling of the wood, combined with action of sunlight and atmospheric pollution. The normal rate of weathering effect is about 1 mm every 12 years. Though slow, the rate of surface deterioration can be prevented by application of adequate painting coats.

iv. Infection of fungi:

Fungi are minute microscopic plants or organisms. They attack timber only when favourable condition for their growth exists, e.g. moisture content in timber, stagnant air around, and warmth.

There are varieties of fungoid growths that attack timber.

They differ in minute particulars, but, in general, their process and effects on the timber are almost similar:

a. Dry rot:

After felling when timber is allowed to remain in forest, it is liable to attack by polyporus vaporarius fungi. Now if the timber is not seasoned properly, the wood in use inherits this fungi growth. Further, if the timber in use is in favourable conditions of contact with moisture/dampness surrounded by stagnant air and the temperature is in the range of 10°C to 24°C, fungus coniphoria puteana grows.

The range of temperature is critical as lower temperature will check them and keep them dormant and higher temperature will destroy them. In such condition infections of many other fungi occur. The malignant and common of these fungi is the Merilius lacrymans. They insert their roots inside the wood and extract food from it and flourish.

These fungi attract moisture to such an extent that sometimes; it hangs in drops or even drips. This moisture accelerates rotting of the timber, which afterwards becomes dry, hence the name dry rot. The dry rot fungus becomes inactive in timber with a moisture content under 18 per cent. All these combined cause rotting of the timber.

b. Wet rot:

Some varieties of fungus cause chemical decomposition of wood of timber and, in doing so, they convert timber into greyish brown powder. This is known to be under attack of wet rot.

The main cause of wet rot is alternate wetting and drying of timber resulting in repeated expansion and contraction causing disruption of fibres and chemical decomposition. This is known as wet rot. When unseasoned or inadequately seasoned timber is used and is exposed to weather, i.e., exposed to rain and wind, it easily becomes vulnerable to wet rot.

To prevent wet rot, properly seasoned timber with a coat of preservative shall be used for exterior works and underground works.

c. Cellar fungi:

These are fungi which grow in cellar condition where ventilation and temperature is less and cause decay of timber.

d. Green house rot:

This is caused due to fungi which flourish in spaces having greenhouse effect, i.e., less ventilation, but enough sun due to which temperature increases and heat is prevented from escaping by convection or radiation.

e. White rot:

This defect occurs when timber is affected by certain type of fungi which attack lignin of wood and assumes the appearance of a white mass consisting of cellulose compounds.

f. Brown rot:

Certain type of fungi remove cellulose compounds from wood and wood assumes a brown colour. This is known as brown rot.

g. Blue stain/sap stain:

Sap of wood is stained to bluish colour by the action of certain type of fungi. They feed on cell contents of sap wood. In doing so sap wood loses colour. This generally occurs when moisture content goes beyond 25%.

v. Common defects:

Apart from the defects occurring due to infection of fungus, the other common defects are:

a. Defect due to conversion:

This occurs during the process of converting timber to commercial forms. Chip marks, diagonal grain, torn grain, and wane are the main defects found in sawn timber.

b. Defects due to attack of insects:

Insects which are usually responsible for causing defect in timber are beetles, marine borers and termites.

vi. Heart rot:

This develops when a branch has come out of a tree. In such case, heart wood is exposed to the attack of atmospheric agents. Ultimately, the tree becomes weak and it gives a hollow sound when struck with a hammer.

vii. Defects due to natural forces:

Natural forces are sometimes responsible for causing defects in timber. They are in the form of abnormal growth, rupture of tissues.

They appear in the shapes of:

a. Knots:

These develop due to knotting of fibres caused by external forces acting constantly upon the tree.

b. Cup shakes:

Separation of annular rings from one another caused by wind and frost in growing tree.

c. Star shakes:

These are radial cracks originating from the centre of the tree and proceeding radially towards the outer edge. These are wider at the outer edge and narrowing at the centre. These are caused due to shrinkage during seasoning.

d. Heart shake:

These are wide splits running right through the heart of a tree. These occur due to incipient decay at the centre.

e. Ring galls:

These are curved swellings, caused generally by the growth of layers over the wound in a timber.

f. Upsets:

These occur when fibres of timber are injured by crushing.

g. Foxiness:

Yellow or red tinge is caused due to incipient decay in timber.

h. Twisted fibre:

This occurs due to constant twisting of the timber in one direction caused by the wind in the forest.

i. Wind cracks:

This is caused by cracking of timber due to strong wind or due to any other external force.

viii. Defects occurring during seasoning:

These defects occur in timber during the process of seasoning and, in general, when the timber, under the process of seasoning, is not matured. The common defects are bow, twist, warp, and cracks due to shrinkage etc.

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Project Report # 5. Fire Resistance and Fire-Proofing of Timber:

The quality of timber to resist fire is essential for saving the structure built from early destruction. Fire resistance of timber is measured by the duration of time in hours; the timber can resist the action of fire.

Grading of the quality of fire resistance depends upon the type of building and varies from 1 hour to 4 hours. In case of an outbreak of fire in a building, timber works become more vulnerable sources for intensifying the hazard.

Fire resistance of timber:

The main disadvantage of using timber as structural element is its affinity to ignite and it gets rapidly destroyed in case of a fire, adding to the intensity of fire. But timber used in sections may attain a degree of fire resistance as timber is a very bad conductor of heat.

This is why time is required to build up sufficient heat so as to cause a flame in timber. To overcome this defect in timber, it is necessary to make it fire resistant effectively.

There are various processes of fire proofing of timber:

i. Application of special chemicals:

a. Timber surface is coated with the solution of certain chemicals. Two coats of solution of Borax or sodium arsenate of 2% strength is quite effective in rendering the timber fire resistant. These are known as fire protective compounds. When temperature rises, the compound either melts or gives off gases which hinder or resist combustion.

b. Timber treated with antipyrine also does not inflame even at high temperature. The antipyrine contains salt of ammonium or boric and phosphoric acids which are considered to be effective in making timber fire resistant.

ii. Sir Abel’s Process:

In this process, the timber surface is cleaned and is coated with a dilute solution of sodium silicate. A creamlike paste of staked fat lime is then applied and, finally, a concentrated solution of silicate of soda is applied on the surface. This process is quite satisfactory in making timber fire resistant.

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Project Report # 6. Preservation of Timber:

Preservation of timber is the treatment of the timber to improve its qualities as construction material. The qualities which are desired to be improved are structural durability, its life cycle in use and protecting the timber from the probable attacks of destroying agents such as fungi, insects, etc.

Preservatives are applied on the surface of the timber with brushes like application of paint. The best way is to keep the timber immersed in preservative solutions like copper sulphate (CuSO₄) for 12 hours.

Preservatives generally used:

i. ASCU treatment, i.e., treatment of timber by the preservative ASCU — Arsenic pentroxide copper sulphate and potasium dichromate or sodium dichromate,

ii. Chemical salts, copper sulphate, etc.

iii. Coal tar,

iv. Creosote oil,

v. Oil paints,

vi. Oil, and

vii. Solignum paints.

These are sprayed on the surface of the timber with the help of sprayer. Tar and creosote shall be applied only on underground and hidden surface of timber where painting would not be required.

Solignum paint:

Solignum is a wood preservative it is very much effective to timber surface subjected to dry rot. It is made of several colours, but brown is generally the most used shade.

Timber to be painted must be clean and absolutely dry. When two coats are recommended, each coat must be thoroughly dried before the next coat is applied.

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Project Report # 7. Seasoning of Timber:

Newly felled timber contains large amount of moisture in the hollow spaces in the cells of woody fibres. The moisture content is about 50% or more by weight in the form of sap. In green timber, after the free water from the cells has dried out, the amount of water remaining varies from 25 to 30 per cent of the dry weight of the wood.

For making the timber suitable for use and for making it durable and resistant to decaying actions, the moisture content is required to be reduced to 10 to 20%. Timber attaining this condition is considered as dry. The process of reduction of moisture content to the desired level is termed ‘seasoning of the timber.’

The art of seasoning is to extract the moisture and limit it to the level according to the variety of the timber.

This may be achieved by:

(a) Natural seasoning or, by

(b) Artificial seasoning or Kiln drying.

Natural seasoning:

In this process the timber is allowed to dry in natural air; hence it is sometimes termed as ‘air seasoning.’

This also can be done in various ways:

i. Stacking in open air:

Timber in log form is stacked in open air. The sap inside comes out due to heat and air action. Obviously it is a time-consuming process and it takes years to season timber in this process.

ii. Stacking under shed:

In this method timber is in scantling form, i.e., sawn timber is kept in stack under a shed having good ventilation. This is also a slow process as the scantlings remain under shed, cracks due to shrinkage or warping is less.

iii. Stacking in a closed shed:

This is an improved method of stacking under a closed shed. Here stacks are made under a closed shed and over a platform. Natural seasoning is economical and simple, but time- consuming, sometimes extending from 2 to 4 years. It does not require any skilled and constant supervision. As seasoning is dependent upon natural air, no control can be exerted over the process.

The timber is kept in stacks; hence drying of different surfaces may not be uniform. The ends need be protected from splitting due to non-uniform drying of the pieces. Possibility of fungi attack remains. It may not be possible to bring down the moisture content to the desired level. Space required for seasoning is large.

Artificial seasoning:

It is a mechanical process. The method has advantage over air seasoning. Defects due to cracking, shrinkage and warping are minimised. It is practically free from any fungi growth due to temperature inside the kiln. All the surfaces are dried equally. Time required is much less, only a few days instead of years.

Better control of circulation of seasoning elements like air, moisture and temperature can be exerted. Moisture content can be controlled as desired. This method is free from atmospheric conditions outside.

Various methods of artificial seasoning:

The different methods are:

i. Boiling,

ii. Chemical seasoning,

iii. Electrical seasoning,

iv. Kiln seasoning, and

v. Water seasoning.

Out of the above processes, the following are more familiar and commercially adopted:

Boiling:

In this method timber in scantling form is kept immersed in a water tank and the water is boiled from within. Due to boiling of the water, the sap of the wood comes out. After three to four hours, the timber is brought out and dried.

Kiln seasoning:

This is widely adopted and is very effective also. In this process, timber in sized form is stacked on a platform in a closed and covered air-tight chamber as shown in Fig. 15.6. Timber is arranged in a chamber so that free circulation of air or steam through the spaces left is not hindered. Air fully saturated with moisture and heated to a temperature of 35°C to 38°C is forced inside the chamber.

As the air is fully saturated it prevents evaporation from the timber surface and heat reaches inside the timber. The relative humidity of the air is then gradually reduced and temperature raised and maintained till the desired moisture content of the timber is reached.

Kiln seasoning, though costly, gives well-seasoned timber as it controls three conditions — circulation of air, relative humidity and temperature.

Water seasoning:

In this process, timber in suitable sections is kept fully immersed in water, preferably in flowing water, the thicker or the larger end facing the flow of water. After 2 to 4 weeks, the timber is taken out and allowed to dry. During the process the flowing water drives the sap and takes its place.

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Project Report # 8. Different Uses of Timber:

Timber is used extensively in almost all construction and repair works.

Timber used in different works may be classified as:

i. Wooden piles — Sal, Pine, or any strong timber having long and straight fibres.

ii. Wooden stairs — Mehogany, Teak, Sisoo, etc.

iii. Door and window frames — Sal, Teak, Holock, Haldi, Iron, etc.

iv. Door and window shutters — Teak, Jack, Gummer, Badam, Oak, Sisoo, Hijal, Arjun, etc. and industrial timber.

v. Props — Sal, Sundari, Pine, etc.

vi. Shuttering — Any strong hard wood, industrial timbers, etc.

vii. Furniture — Mahogany, Teak, Badam, Holock, Jack, etc.

viii. Beams — Sal, Teak, etc.

ix. Posts — Sal, Teak, Iron wood, etc.

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Project Report # 9. Structural Properties of Timber:

Structural properties of timber vary widely according to the species of timber, region of their growth, location of the section, structure of the fibre, slope of fibre, grade of timber, grain, etc. I.S. Code 883-1970 specifies the structural properties of different types of timbers in consideration of all the variations.

Timber is classified in consideration of the structural strength as Grade A, Grade B, and Grade C according to its modulus of elasticity:

Project Report # 10. Substitutes for Normally Used Timber:

i. Second Grade Timber:

These timber — Mango, Jackfruit, Jamrul, Haldi, Hollock, etc., were not generally used in construction. These were known as firewood. But these timbers when properly seasoned and treated perform equally well and satisfactory as Grade ‘A’ timber. Door and window frames and shutters are still preferred to be made of timber.

Due to scarcity of quality timbers, these are largely manufactured of second grade timber, seasoned and treated. There are factories manufacturing machine-made frames and shutters which are better in performance and economical than those made of conventional species of timber.

ii. Steel Door and Window Frames and Shutters:

Frames and shutters made of steel sections are better in performance and economical. However, this again encroaches upon another scarce material, steel. Steel door and window frames and shutters are not liked in residential buildings; but are welcomed in other non-­residential structures.

Aluminium door and window frames and shutters are elegant and economical when compared with the cost in use of the wooden and steel frames and shutters. But due to their higher initial cost, these have not been able to replace timber frames and shutters.

iii. Industrial Timber:

Various industrial timbers in the form of boards and panels have been developed and are largely available in the market. These are suitable for making door and window shutters and furniture and are equally good as the traditional timber used in this industry and sometimes are better than those.

These materials have substituted timber in construction fields substantially. These are termed as industrial timber. Industrial timber is manufactured scientifically in factories. These timbers possess the desired shape, appearance and strength.

The following are the varieties of industrial timber available in the market:

a. Veneer:

Veneers are very thin sheets or slices of wood, thickness varying from 0.40 mm to 0.60 mm or more, obtained by rotating a log of wood against a sharps knife. The slices are then dried in air or in kilns for removing moisture. These are used as covering over other wood sections by glueing to improve appearance or are used for manufacture of plywood.

b. Plywood:

The term ‘ply’ means thin layer, veneer. Ply-woods are boards manufactured by pasting thin layer of wood or veneers and held in position by adhesive. A ply-board is made of a number of plies for having the desired thickness and quality. The veneers are placed normal to each other to increase the longitudinal and transverse strength of ply-boards.

The veneers are glued under pressure either hot or cold. When pressed hot, the temperature varies from 150 °C to 260°C cold pressure is applied at room temperature. The applied pressure varies from 7 to 14 kg per sq cm.

Ply-boards are available in thickness of 4 mm to 20 mm.

Ply-boards are used for various purposes — making door and window shutters, ceilings, partition walls, furniture, etc.

c. Particle-boards:

Particle-boards are made of plies and wood particles. Wood particles of size 6 to 10 mm with glue (resin) are sandwiched in between two plies of timber. Plies are generally 3-4 mm thick. The whole thing is pressed to make a compact board. Thickness of the particle-boards is varied by the thickness of the particle fill (not the size of the particles),

Particle-boards are available in thickness of 10 mm to 40 mm.

Particle-boards are used for various purposes — making door and window shutters, ceilings, partition walls, furniture, etc.

d. Block-boards:

These are variation of ply-boards. Pieces of wood of same thickness are placed in between two layers of plies and pressed with glue to produce block-boards. These are available in thickness of 15 to 50 mm. These are used for making door and window shutters, partition walls, ceilings, etc.

e. Batten-boards:

These are made of solid core of sawn timber of thickness 20/25 mm and covered by ply sheets, making the total thickness of 50 mm. The direction of the grains of the core battens is at right-angles to the adjacent outer ply sheets.

These boards are light in weight and strong. They do not crack or split easily. These are used for making furniture, walls, packing pieces, ceilings, door and window shutters, etc.

f. Fibre-boards:

These are rigid boards. These are known as pressed wood or restructured wood. Thickness of the boards varies from 5 mm to 12 mm.

Manufacture of fibre-boards:

Pieces of soft wood, cane or such other vegetables are heated in water and are separated. Steam under pressure is then admitted to the vessel, pressure is then increased to 70 kg per sq cm. Steam, when released, makes the wood pieces explode and fibres get separated.

The fibres flow out. They are then cleaned and spread in the form of sheets or blankets of required thickness. Such loose sheets of wood fibres are prepared between steel plates and are pressed with glue and the fibre- boards are obtained.

Fibre-boards are commercially available in the names of masonite, Norder, Treetex, etc. and are used for all types of decorative finishes.

Impreg-timber:

Timber, partly or fully covered with or impregnated with resin, is called impreg-timber. These are manufactured by immersing thin strips of timber or veneers in resins like phenol formaldyhyde which are soluble in water. The resin impregs in the timber and fills the space between wood cells and by chemical reaction a consolidated mass is formed. The timber is then cured under temperature at 150°C to 160°C.

Impreg-timber is available in the name of Formica, Sungloss sunmica, etc. and is used for decorative works, furniture making, etc.

Compreg-timber:

The process of manufacture of compreg-timber is the same as that of impreg-timber, the only deviation is that during curing pressure is applied to increase the strength of the timber.

Uses of compreg-timber are also the same as that of the impreg-timber.

iv. Medium Density Fibre-Boards (MDF):

The base of the industrial timber discussed so far is timber or wood, which means that these are not actually substitutes of timber as such; but are for replacing the traditional high grade costly timber e.g., Teek, Sal, Sisoo, Mahogany, etc.

However, in manufacture of these industrial timbers, low grade timbers which were so long known as fire-woods are used. Thus, those substitute timbers are now considered essential for manufacture of door and window frames, shutters, furniture, etc.

In continuous search for perfect natural wood substitute, many products have been devised. Each has its advantages and disadvantages. NUWUD is one of them.

NUWUD is manufactured from agro-based lignocellulosic fibre of the same size uniform resin content throughout the thickness.

Manufacturing process of NUWUD is more or less similar to fibre boards. Agro-based cotton stalks (stems of plants) are chipped, sieved, graded and washed. These are then boiled in a vessel for separating the fibres.

The fibres are then distributed uniformly throughout in a mat form in layers of two opposite directions. Resin is blended ensuring uniform distribution. The fibres are then dried. The mat thus formed is compressed 10-20 times for obtaining an optimum thickness.

The desired thickness is thus achieved. The mat is then trimmed for perfect uniform thickness.

The panels are then passed through cooling wheels to bring down the temperature from 80°C to 45°C. Sides are then trimmed and finished and the panels are sent in storage.

The material can be used for all sorts of works where hitherto only high grade timber was used, from architectural joinery to cabinet making, v. Syntex door and windows

v. Syntex Door and Windows:

Readymade door and window shutters with frames made of non-decomposable PVC based material named Syntex are available which can be used suitably. However, these doors and windows — though suitable in exposed places and bathrooms where the shutters would remain constantly in contact of moisture — are not favoured in other places for aesthetic reasons. Similar shutters have been developed by many other manufacturers.

vi. Reinforced Concrete Door and Window Frames:

R.C.C. door and window frames are elements fabricated -in the exact shape and size of timber frame. After fixing and finishing with coats of paint, these would look like timber frames.

The fixing of door and window leaves may pose some difficulty, but the same can be fixed with the help of steel lugs or embedded wooden blocks in the frame during casting for holding the hinges. In case of three-piece frame for door, a detachable horizontal piece or separator of timber or steel section shall be fixed at the bottom temporarily during transport and erection at site.

The cost of R.C.C. frames would be cheaper than timber frames. These are more durable and would offer better resistance to fire, weather and termite attack.

vii. Glass Reinforced Gypsum (GRG) Board:

GRG boards have been developed by the Central Glass and Ceramic Research Institute, Calcutta. These can be used as potential substitutes of wood.

The raw materials required are ‘Plaster of Paris’ and glass fibres in the form of ravings. The fibres are uniformly distributed in Plaster of Paris for making panels of size 2,000 x 1,000 mm and thickness 4 mm.

The panels can be used for making door panels, false ceilings, partitions, furniture, etc. The material is pseudo ductile in nature having flexural strength of 20 to 35 N/mm² and impact strength-in the range of 10 to 20 N/mm².

The material is fire proof, insect proof and rot proof. Unlike wood it is isotopic in nature and has equal strength in all directions. Workmanship is like that of wood and can hold screws. The surface can be treated as in case of wood by polishing or painting.

viii. Glass Reinforced Concrete (GRC) Panel:

Glass reinforced concrete panels are fabricated out of cement concrete reinforced by glass fibres. These are generally used for making decorative perforated panels of thickness 50 mm and used as rails or claustras.

Project Report # 11. Timber as Construction Material:

Timber is used in building industry in various ways. It may be used as piles in foundation, as beams and rafters, as planks in timber grillage foundation, as posts. It is used in making door and window frames and shutters, roof truss and various other items of work including making of furniture. Use of timber in shuttering and scaffolding for construction and maintenance works is very common.

Due to scarcity and exorbitant rise in price of timber, the timber which were used normally, e.g. Sal, Teak, etc., are being replaced by hard woods, and other woods e.g., Haldi, Gamar etc.

However, if these timbers are properly seasoned and treated, there shall be nothing against using them. Various substitutes have come up and are gradually replacing timber in the building industry. Still, it will be a long time before timber is replaced fully or in other woods it will never be possible to eliminate timber from the construction industry.

Repairing of Timber Roof Truss:

In timber roof truss, generally purlins give way due to load of covering (tile) or due to heavy thrust falling on the roof or due to bad quality of timber having knots. In such cases, the covering shall be removed exposing the damaged portion and then the damaged or broken purlin shall be removed and replaced. If the old purlin was otherwise in good condition, the same may be repaired by normal timber joinery and re-fixed.

The same process may be adopted in case of rafters, etc.

Protection of Timber Works:

The timber works whether in posts, door and window frames, shutters, or in other places need be protected by painting against weather action, termite ingress, insect attack or attack of rots.

The timber work needs ventilation to ensure longer life. Hence, care shall be taken to see that the timber members are not blocked against normal ventilation. These shall be protected against weather action, specially against coming in contact with water or moisture.

Cracks in Door and Window Frames and Joinery:

Cracks in woodwork are basically due to initial drying of the timber and could appear very ugly. They are mainly due to use of unseasoned timber in construction. Shrinkage in woodwork in a direction normal to the grains is quite substantial. As preventive measure against opening out of joints and warping of wood, only properly seasoned timber should be used in work.

When cracks are caused in woodwork, these could be filled up with good quality putty made by mixing paint, whiting and thereafter applying one or two coats of paint to check further moisture movement.

Occurrence of Cracks of Glass Panes in Door and Window Shutters:

i. Rabbet for fixing glass panes not filled evenly with putty before fixing the panes in position. Glass panes rattle due to wind pressure causing development of cracks in the panes. Back putty in the rabbet should be uniform and on entire length.

ii. Glass panes fixed without adequate and uniform clearance in the rabbet all round, may crack due to thermal expansion. Exposure to sun and rain cause rusting of steel window frames and cause cracks in glass panes. As preventive measure, adequate and uniform clearance between glass panes and frame either of timber or steel should be kept.