Floors are the horizontal units of a building structure which divide the building into different levels. The purpose of separation or division is to create more accommodation within a restricted space one above the other for different purposes, viz., to provide support for the occupants, to allow space for furniture and equipment, etc. Strictly, the division of vertical occupation is called floors and the exposed top surfaces of floors are termed as floorings. But in usage, both the terms reflect the same meaning.

Thus the floor of a building immediately above the ground is known as the ground floor. The construction below the ground level or the building has a basement, the floor is termed as the basement floor. The top portion of a ceiling forms the first floor or an upper floor. Any subsequent top portions of ceilings form upper floors.

The major problems of ground and basement floors are dampness removal and protection from heat. Generally, there will be no problem regarding strength and stability for ground and basement floors as they get full support from the ground. The major problems of upper floors are strength and stability.

FUNCTIONS OF A FLOOR

A floor consists of a sub-floor and a floor covering.

Sub-floor may be a base-course or a sub-grade. This is required to impart strength and stability to support a floor covering and all other super-imposed loads including live loads. Floor covering or paving or simply as flooring is the one constructed over the sub-floor and is intended to provide a hard, clean, smooth, impervious, durable and impressive surface to the floor.

The functional requirements of floors, in general, are as follows:

(i) Strength and stability

(ii) Damp prevention

(iii) Heat insulation

(iv) Sound insulation

(v) Fire resistance

(vi) Durability

SELECTION OF FLOORS

In order to select a suitable type of floor construction in a building, certain factors have to be considered. Although certain points may be common for ground, upper and basement floors, some distinct different points are to be observed in certain cases.

Ground Floors

For ground floors, the selection of the type of the wearing surface is important and the other factors which need consideration are given below:

(i)     Initial cost

(ii)    Appearance

(iii)    Durability

(iv)    Cleanliness

(v)    Thermal insulation

(vi)    Dampness

(vii)   Indentation

(viii)  Noiselessness

(ix)    Maintenance

(x)    Fire resistance

Upper Floors

Selection of a suitable type of construction for upper floors of a building depend on the following main factors:

(i)     Initial cost

(ii)    Floor loads

(iii)    Type of construction

(iv)    Plan of the building

(v)    Function of the building

(vi)    Fire resistance

(vii)   Sound insulation

(viii)  Type of ceiling

(ix)    Wearing surface

(x)    Weight and position of floors

Basement Floor

It is not a routine type of floor provided in every building. It is provided for a particular type of buildings like apartments, hotels and restaurants, cinema halls, etc. The selection of basement floors depends on the following factors:

(i) Initial cost

(ii) Availability of ventilation

(iii) Drainage of water from the floor

(iv) Adequate safety against fire

(v) Groundwater level

TYPES OF GROUND FLOORS

As the ground floor directly rests on the ground, there is no need for a sub-floor. In order to drain the water outside completely, adequate drainage arrangements have to be made beneath the floor.

In normal practice, the space above the ground, up to a height of about 25–30 cm below the plinth level, called the basement, is filled with some inert materials like sand, gravel, crushed stone, cinder, etc. Over this course, a damp-proof course if needed is laid. Otherwise, the floor covering is laid directly on the uniform bed.

The materials used for ground floor construction are: bricks, stones, concrete, hollow concrete blocks or wooden blocks.

The materials generally used for floor coverings are bricks, concrete, terrazzo tiles, marbles, stones, mosaic, wood, etc.

Stone Floors

Usual sizes of stones of 30 cm × 30 cm, 45 cm × 45 cm or 60 cm × 60 cm with a thickness of 2–4 cm are used. Generally, square stone slabs of the above sizes are used but the slabs can be rectangular or oblong in shape with square edges. Stone slabs are laid on concrete bedding.

Before laying the slab a base is prepared after excavating to the required depth and the earthen base is levelled, rammed and watered. A layer of lime concrete of thickness 10–45 cm is spread over which the concrete bed or sub-grade is laid.

After setting the stone floor with a slope of 1 in 40, the mortar joints are raked out to a depth of 2 cm and flush pointed with cement mortar of 1 : 3.

Following aspects are kept in mind while laying stone slabs, Fig. below:

(i) To begin with two stone slabs from diagonally opposite corners are laid. A string is stretched touching these corner slabs so as to fix top level of the floor.

(ii) Intermediate slabs are placed from both sides taking care that the tops of stone slabs are touching the string which ensures the provision of proper grade.

(iii) All stone slabs should be of uniform thickness, strength and well-drained on edges for residential and public buildings.

(iv) Width of joints between the slabs should not exceed 0.5 cm.

(v) Rough surface stone, may be used for godown, sheds, stores, etc.

Stone flooring

Brick Floors

This type of flooring is used in case of warehouses, stores and godowns. This is a cheap construction and used in areas when stones are not available but good quality bricks are available.

This flooring may be laid flat or on edge. They may be arranged in a herringbone pattern or at right angles to the walls. Brick on edge is preferred compared to bricks laid flat as the brick on edge is less liable for crack under pressure because of the higher depths. The bricks, in both the cases, are laid on ordinary mortar and pointed with cement or set in hydraulic mortar.

The construction of brick flooring is done as explained below, Fig. below:

(i) An excavation of about 40 cm depth below the intended level of the floor is made.

(ii) The earth surface is levelled, watered and well rimmed until it is dry and hard.

(iii) Over the earth, above a sub-grade of 25 cm depth consisting of rubble or brickbats is laid.

(iv) Over this, a 10 –15 cm thick layer of lime concrete or lean cement concrete (1:3:6) is laid.

(v) Upon this prepared sub-grade, bricks are laid in the desired shape.

Brick flooring

Concrete Floors

Concrete floorings are mostly used in all residential, commercial and public buildings. The flooring is constructed adopting either monolithic or non-monolithic construction.

In the monolithic construction, after laying the base course layer, immediately a concrete topping is provided. In this type of construction, only a small thickness is needed for the wearing surface as the bond between the base course and the wearing surface is good.

But this type of flooring has got several disadvantages as explained below:

(i) The wearing the surface is susceptible for damage due to subsequent floor use.

(ii) As the base course if undergoing only a small settlement immediately, there is a possibility for hair cracks.

(iii) Repairing the damaged top surface is difficult.

(iv) The progress is slow as the base course has to settle.

Non-monolithic construction is sound as the wearing surface is laid only after adequate drying of the base course. The floor finish generally used is an ordinary concrete finish of 1:11:3 (Fig. 23.3). Under controlled conditions, a mix of 1:2:4 ratio with carefully selected aggregates may be used.

For non-monolithic construction, the surface of the base concrete is brushed with a stiff broom and cleaned thoroughly. The surface is wetted and excess water removed. The floor is laid in rectangular panels not greater than 2 × 2 m. Generally, alternate bays are concreted so as to avoid initial shrinkages. When the concrete layer is even, the surface is rapidly compacted by remaining or beating and screeded to a uniform level. Then trowelling is done to give a level smooth surface. Adequate curing is done for 7 days by spreading a layer of wet sand or special membrane may be used.

Concrete Floors

Granolithic Floors

It is a concrete flooring with a different type of floor finish called granolithic. Granolithic finish is concrete made of specially selected aggregate. The thickness of the layer varies from

1.25 to 4 cm. When it is greater than 4 cm this may be laid monolithically or after the base concrete has hardened.

This flooring is made with very hard and tough quality aggregate in rich concrete of 1:1: 2. Generally, hard fine-grained granite, basalt, limestone and quartzite stones are suit- able for coarse aggregate. In order to get a better granolithic finish, the aggregate may be crushed and used. The fine aggregates are the natural or crushed sands with a suitable gathering. Non-slippery surfaces can be obtained by adding suitable abrasives. In case of non-monolithic construction, the base course may be prepared as done in concrete flooring. Granolithic flooring has all the advantages of concrete flooring.

Terrazo Floors

Terrazo is a special type of concrete flooring containing marble chips as aggregates. Any designed colour and designs can be obtained by using marble chips of different shades and colour cement.

Terrazo mix of 1: 2 or 1: 3 (1 cement to 2–3 marble chips) is used depending on the size of marble chips. Terrazo finish is of 10 mm thick. The terrazzo finish is laid over the concrete base course (as explained in concrete flooring) by two methods.

(i) The cement concrete base is covered uniformly by a 6 mm thick sand cushion and a tar paper is placed on this. Over this paper, a layer of rich mortar (1 : 3) about 30 mm is placed uniformly.

(ii) A thin coat of cement is spread over the wet concrete base. This layer is cleaned and a layer of cement mortar 12 mm thick is spread evenly over it. When the mortar bed has hardened the terrazzo mix (1 cement : 3 marble chips) of 6 and 12 mm is laid after adding water and making the workable mix.

After curing for several days, the surface is polished by means of a grinding machine fitted with a carborundum grinding stone disc. During grinding the surface is kept wet and small holes or pores are filled with a suitable cement paste matching the surface configuration. The surface is then washed with a weak solution of soft soap in warm water. Such a finished surface gives a pleasing appearance and a clean environment.

This type of floor is used in public buildings like banks, hotels, offices, etc., because of its decorative appearance and excellent wear-resisting properties.

Mosaic Floors

For the construction of this type of flooring, a hard concrete base is laid first. When the base is wet, a 2 cm thick layer of cement mortar (1: 2) is evenly laid. Over this layer, small pieces of broken tiles are arranged in different patterns. After this, the inner space between tiles is filled with coloured pieces of marble in the desired fashion.

Following this cement or coloured cement is sprinkled at the top to get a complete floor without pores. Then the surface is rolled by a light stone roller till an even surface is obtained. After 24 hours of drying the surface is rubbed with a pumice stone of 20 cm × 20 cm × 7 cm fitted to a long wooden handle. This polished surface is allowed to dry for 2 weeks before put into use.

Tiled Floors

In this type of flooring tiles either of clay or cement concrete, manufactured in different shapes, are used. A 15 cm thick layer or lime or cement concrete is laid over the levelled ground. In order to receive the tiles at 25 mm thick layer of lime mortar (1: 3) or cement mortar (1:1) is laid. A cement slurry is spread over the hardened mortar. Tiles are laid flat on this bed and a cement paste is applied on the sides. Joints are rubbed with carborundum stone after allowing 2–3 days for setting. The entire surface is polished with a pumice stone (Fig below).

Tiled Floors

Tiled floorings are used in residential buildings, hotels, offices and other public buildings. These floors can be constructed in a very short time with a pleasing appearance and good durability.

Asphalt Floors

Asphalt floorings are of two types, viz., (i) using asphalt tiles and (ii) using mastic asphalt. Asphalt tiles are made from asphalt, asbestos fibres and other materials and pressed under pressure. Asphalt mastic is a mixture of fine aggregates and natural or artificial asphalt.

Asphalt tiles are used to cover wooden or concrete floors. These tiles are resilient, non-absorbent, moisture-proof and cheap. They are used in schools, offices and hospitals, etc.

Asphaltic mastic can be mixed hot and laid in continuous sheets or pressed into blocks which can be used for flooring. As an alternative, it may be mixed with oil and asbestos and applied cold. An ordinary concrete or wood base may be used for laying this mixture.

Marble Floors

High quality marble slabs in the required sizes and colours are available in the market. The construction procedure is the same as that of mosaic flooring except for that marble slabs or pieces are used instead of mosaic tiles or pieces. This type of flooring is preferred when sanitation and cleanliness are required as in the case of hospitals, temples, theatres and another superior type of works. Nowadays some quality marbles are used for residential buildings also.

Timber Floors

Timber flooring is not generally preferred for ground floors. If it is used as a ground floor, the prevention of dampness is most important. Timber floorings can be provided in any one of the following methods. Strip flooring consists of narrow and thin strips of wood joined to each other by tongue and groove joint. Planked flooring is one type in which wider planks are used and they are also of tongued and grooved type. Wooden block flooring consists of small square or rectangular blocks with tongue and groove joints, Fig. below

Timber flooring should have a concrete base or should rest on joints spanning across dwarf walls which are constructed at suitable intervals. For fixing the timber floors on concrete slabs, longitudinal nailing strips are provided. Planked flooring should be laid with spaces of metals spaced 1 mm apart temporarily for providing expansion joints. Strip flooring is used in thickness of 2–2.5 cm and width of 6–10 cm.

TYPES OF UPPER FLOORS

Upper floors should be strong to take heavy loads, should have sound insulation and fire resistance and also have a good wearing resistance. The upper floors are generally classified based on the materials of construction arrangement of beams and girders or materials used.

Commonly used floors are explained below.

Timber Floors

Timber floors are used only in areas where more timber is available at a reasonable cost. Further, they are used for residential buildings where the span is less and load on the floor is less.

The floors may be of a single joist, double joist or triple joist. Joists of floors should be strong enough and not deflect too much causing any cracking of plaster of the ceiling. Further long joists need strutting to avoid buckling. The planking consists of wooden boards of 4 cm thickness and 10–15 cm wide. The figure below shows the details of a single joist timber floor, and the details of the joist’s joint are shown separately.

Details of single-joint timber floor

Jack Arch Brick Floors

Bricks and plain concrete can not be used directly as a flooring system without proper strengthening. Either reinforcement can be provided or provision can be made so as to develop arch action.

Rolled steel joists (RSJ) are used to build arches so as to form jack arch floorings. The arches have spares varying from 1.25 to 2 m and the rise is 1/12th to 1/16th of the span. In order to accomplish the end thrusts the rods of 2–2.5 cm are run at 2–2.75m apart as shown in Fig below. The rods are encased in the wall along with an RSJ. The spandulus are filled with concrete.

Brick jack arches are constructed by bringing up the arches by laying the bricks on edges starting from the ends where the bottom of an RSJ is concreted. Lime or cement mortar is used. After laying the brick from ends, the key brick is introduced to set the arch action. Next layer is laid by pushing the centring ahead. This operation is continued till the work is completed.

Brick jack arch floor

RCC Slab Floors

All modern buildings are invariably constructed with reinforced cement concrete. For small spans a simple RCC slab floor is generally suitable. For rooms, with the ratio of length of the room to its width is greater than 1.5, slabs are designed to span along the shorter width. That is, the main reinforcements are placed to the shorter width. The thickness of the slab depends on the type of concrete used, the span, floor loads, etc. These slabs are considered along with a frame then it is made monolithically with the supporting frames (Fig. below).

RCC slab floor

If the spans of rooms are approximately equal then the slab is designed as a two-way slab (i.e., main reinforcements are placed parallel to both the spans). At corners suitable reinforcement is provided at top and bottom to take the stresses due to partial fixity.

Reinforced concrete slabs are laid adopting the routine mixing, laying, finishing and curing. The slab provides a very smooth surface at the bottom and a pleasing appearance. It also accommodates all lighting arrangements. The RCC slabs are restricted up to 4 m span beyond which beam and slab construction has to be adopted.

The following is the construction procedure:

(i) A centring of steel or timber is erected to support its own weight and the superimposed load.

(ii) The reinforcement is placed on the centring before coating a thin layer (2–5 cm) of cement concrete.

(iii) The required mix of cement concrete is then prepared and poured around the reinforcement up to the required thickness of the slab.

(iv) The concrete is well consolidated by ramming or using a vibrator.

(v) The concrete is cured for a minimum period of 2 weeks to attain its full strength.

(vi) After the concrete has sufficiently hardened, the formwork is recovered.

(vii) The upper and lower surfaces of the slab are plastered and required finish is given.

RCC Beam and Slab Floors

For larger spans and heavy loading conditions, RCC beam and slab construction is generally resorted to. This type of construction is commonly used for most of important buildings (Fig. below).

RCC T-Beam Slab Floors

In this type of floor, beams and slabs are designed as rectangular sections and the slabs are supported on beams. It is a monolithic construction both the beams and slabs are cast together. The beam used in monolithic construction is called a T-beam (i.e., a part of the slab acts as a flange of the T-beam).

The main reinforcement of the slab runs parallel to the short span. However, some reinforcement is provided on the other, as in RCC slab floor, as distributors. In the case of equal spans, two-way slabs may be constructed with reinforcement provided on both directions. Sometimes the projecting beams are covered by providing a false ceiling underneath it (Fig. below).

RCC T-beam slab floor

The construction procedure is same as that of RCC slab floor, except for the type of centring or formwork required for the floor.

Flat Slab Floors

This type of floor is called a beamless slab floor. This flat-slab floor is directly supported on columns without any intermediate beams. This type of floor is preferred where heavy loads are anticipated and where there is headroom restriction. The columns supporting the floor are invariably circular in cross-section and the tops of the column are flared or tapered, which is called as capital. Sometimes a certain portion of the slab, symmetrical with the column, is thickened which is called drop panel (Fig. below).

Flat slab floor

The flat slab floors have several advantages which are given below:

(i) As there is no projection of beam, there is no need for an additional ceiling.

(ii) More clean headroom is available.

(iii) Better ventilation and lighting is available.

(iv) Even for heavier loads only thin slab thickness is needed.

(v) The construction is comparatively easier.

The flat slab floors are preferred under the following conditions:

(i) When large equal number of panels are required.

(ii) Where clear large spans are required.

(iii) Where there is a limitation in headroom.

(iv) The ratio of length to breadth of panels is to be more than 4 : 3.

(v) The difference between the length and breadth of any two adjacent panels should not be more than 10% of the greater of the two.

The following two types of systems of reinforcement are in use: (i) two-way system and

(ii) four-way system.

In the two-way system of reinforcement, the reinforcement is provided between the columns and perpendicular to the columns. The area left is considered as supported on four sides.

In the four-way system of reinforcement, the reinforcement is placed in four directions. That is two rows of main steel from column to column and other two rows placed diagonally across the panel from column to column.

Resilient Floors

Floors made from materials such as PVC, linoleum, rubber, etc., are called resilient floors. Resilient floors are soundproof and dust free and are used in libraries, offices, computer rooms, showrooms, etc. The three important resilient floors are: (i) PVC (Vinyl floors), Linoleum floor and Rubber floor, which are briefed below.

1. PVC Floor

The material in PVC floors is the thermoplastic binder which can be vinyl chloride poly- mer or vinyl chloride copolymer or both. The floor covering is backed with hessian or other woven fabric. Vinyl asbestos tiles have 40% of chrysotile asbestos fibre together with powdered mineral fillers and pigments. The thickness of normal PVC floor coverings are 1.5, 2.0, 2.5, 3.0 and 4.00 mm and the thickness of back floor coverings come in 2.0,

2.5, 3.0, 4.0 and 5.0 mm sizes. In roll form it is usually available in 1.0, 1.5 and 2.0 m and lengths of 10 m.

2. Linoleum Floor

Linoleum is a covering materials generally laid over wooden or concrete floors. Linoleum material is lubricated by mixing oxidised linseed oil with gum, resin, pigments, wood floor, cork dust and other filler materials. It is available as rolls of 2 or 4 m width with 2–2.5 m thick and both in plain and printed forms. Linoleum coverings are fixed to the sub-floor by means of suitable adhesive in order to have adequate bond and high durability. In some cases, it is nailed at the edges.

3. Rubber Floor

It is composed of natural rubber with various filling compounds. As the cost of rubber is high, their type of floor is expensive. They are produced in sheets and also in tile form. A sub-floor is essential.

Hollow Block and Rib Floors

In this type of floors, to reduce the total weight of the floor hollow blocks of clay or concrete are used. In one type, the blocks are placed at 10 cm apart and in this space, mild steel bars are placed (Fig. below). Suitable flooring at top and ceiling finish are provided. In order to develop enough bond with the concrete, the blocks are provided with rough or grooved surface.

Hollow block and rib floor

The structural hollow clay floor tiles should be free from cracks and of uniform colour and texture. Projections of tiles are kept on one of the external face of such tiles so as to facilitate the application of plaster. The dimensions of length, 45–90 cm, width, 19–24 cm and height 70–90 mm. The weight per metre length of structural hollow clay tiles does not exceed 140 N.

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SOURCE: Basic Civil Engineering

Fourth Edition

MS. Palanichamy

Vice-Chairman

Tamil Nadu State Council for Technical Education Chennai, Tamil Nadu

LIGHTING BASICS

Lighting is measured by the amount of luminous flux on a surface, called illuminance. It is expressed either in foot-candles (illuminance in a square foot) or in lux (illuminance in a square meter). An artificial light source is referred to as a lamp. Although lamps are commonly identified by their wattage, this does not describe the output of light. A watt is the measurement of energy consumption from a particular light source. So an incandescent lamp and a fluorescent lamp can have the same light output of foot-candles or lux while ranging dramatically in wattage. As an example, a 60-watt incandescent lamp has the same light output as a 15-watt fluorescent lamp.

Light coming from a single point source can, like direct sunlight, create dark areas of shadow around the pool of light it provides. A point source calls attention to the surface it is illuminating and highlights its inherent characteristics. Diffuse light, like that on a cloudy day, distributes light evenly and is not strong enough to create shadows. While this even distribution of light may be good in a working environment because it is easy on the eyes, it can seem a bit dull and lifeless over time.

An unshaded lamp or poorly positioned fixture with an exposed lamp can cause extreme brightness from a light source called glare. While not measurable, glare is easily recognizable. It can impair vision and induce discomfort as the eye usually squints to reduce the impact of its harshness. Veiling reflection is another type of glare that is caused by the brightness of

a light source reflecting off a shiny surface such as glass. A familiar example might be the reflection of a bright window on a computer screen. The well-thought-out distribution and location of light fixtures can reduce glare significantly.

TYPES OF LAMPS

Many types of lamps are available, each with specific characteristics for colour rendition, size, energy consumption, and lamp life. Juggling all the variables can be complex. To specify lamps correctly, designers should know their efficacy rating (1 = low/poor, 5 = high/excellent) as well as their correlated colour temperature and colour rendering index.

Correlated Color Temperature

Color Rendering Index (CRI)

NEW LIGHTING TECHNOLOGIES

Although fibre-optic and LED lighting technologies have been around for a while, they are now becoming more readily available to designers. Both lighting types are more energy-efficient than fluorescent lighting, but also much more cost-prohibitive. As the market continues to focus on energy efficiency, however, designers will see these technologies advance further and become more affordable.

Fibre-Optic Lighting

This technology relies on strands of acrylic cables to transmit light from the light source, called the illuminator, to the ends of the cables. The illuminator is simply a box with either a tungsten halogen lamp or a metal halide lamp of varying wattages. Tungsten halogen lamps are more common, while metal halide lamps are typically used for large installations. The ends of the acrylic cable are gathered in a bundle and placed in an aperture directly in front of the lamp. The illuminators should be conveniently located for easy access to relamp the fixtures. It is also important to note that the illuminators need ventilation to release the heat that is generated by the lamp.

Depending on the lighting design, there can be less than a handful of acrylic cables or hundreds of cables. The length of the cables can vary per installation, but as a general rule, they should not exceed 50 feet (15 meters) or light transmission will be compromised. The advantage of this system is that multiple lights can be located in difficult-to-access places, controlled by a single lamp inside the illuminator.

LED Lighting

Although light-emitting diodes (LEDs) use a fraction of the electricity and last up to ten times as long as fluorescent lamps, they are too costly for use in general lighting. LEDs are available in high intensities of red, green, and blue light, and the combination of all three coloured lights

Comparative Correlated Color Temperature

yields white light. Varying combinations of the three colours can produce a full spectrum of colour options. LEDs have the additional advantage of producing no heat. Currently, LEDs are used in interior design to create desired effects such as accenting a reveal or washing a wall with coloured light. As the technology advances, it will become more affordable and eventually be applied to general-purpose lighting.

LIGHTING TERMINOLOGY

Ballast: a small device that controls the flow of current by providing the required starting voltage and then reducing the current during operation.

Correlated Colour Temperature (CCT): spectral characteristic of a light source, measured in Kelvins (K). The lower the temperature, the warmer the (yellow/red) tones; the higher the temperature, the cooler the (blue) tones. sunlight at dawn has a colour temperature of 1900K while a uniform overcast sky is 6527K.

Colour Rendering Index (CRI): scale from 1 to 100 that describes the effect of a light source on an object or surface. The higher the index, the more natural and vibrant the object appears.

Dimming Ballast: Device used with fluorescent lamps to vary the output of light by the use of a dimmer control.

Efficacy, or Luminous Efficacy: Efficiency in which electrical power is converted to light. Efficacy measures the number of lumens emitted per watts consumed (lm/W).

Low-voltage Lamp: Incandescent lamp that operates with low voltage, ranging from 6 to 12 volts.

Luminance: Amount of light reflected or transmitted by an object.

Transformer: The device designed to raise or lower electric voltage.

MATERIALS USED FOR DAMP PROOFING (DPC)

There are various materials, which are used as damp-proof courses depending upon the location, economy and degree of damp proofing desired. However, while selecting a particular damp-proofing material, the following requirements of an ideal damp-proofing material should be remembered.

1. The material for DPC should be impervious and durable, i.e., the material should be effective during the useful life of the building.

2. The material should be capable of resisting both dead loads and superimposed loads without being disintegrated.

3. The material should remain steady in its position, without any movements, so that the walls overlying the DPC do not develop any cracks.

4. For DPC above the ground level, with wall thickness up to 40 cm, any material listed below for DPC can be used.

5. For DPC to be laid over larger areas, such as floors and roofs, and thicker walls, a DPC material that provides a lesser number of joints should be used, such as mastic asphalt, bitumen sheeting and plastic sheeting.

6. The material for parapet walls and in other situations where differential thermal movements are expected due to exposure should be of flexible material, like mastic asphalt, bituminous felt and metal sheets.

7. In water-retaining structures or situations, a jointless DPC should be provided to take care of the risk of leakage.

8. In the cavity or hollow walls, the cavity over the door or window openings should be bridged by flexible materials, like bitumen sheets, strips of lead and copper.

The materials generally used for DPC are listed below.

1. Flexible materials: Hot bitumen, bituminous felts, bituminous sheet, plastic sheet (polythene sheets), metal sheets of lead, copper, etc.

2. Semi-rigid materials: Mastic asphalt or a combination of materials or layers.

3. Rigid materials: Use of I-class bricks, stones, slates, etc.

Hot bitumen or hot asphalt

This is a flexible material, which is first heated and then spread over the bedding of concrete or mortar (i.e., over walls). This should not be applied in thickness less than 3 mm. Bitumen or asphalt forms an excellent damp-proof course, as it offers an impervious, indestructible and tough surface.

Bituminous felts (6 mm thick sheet or asphaltic felt)

This is also a flexible material, which is available in rolls of normal wall widths. For placing this in position, first a layer of cement mortar is laid on the brickwork and then DPC is bedded on it. An overlap of 10 cm in case of joints and full-width overlap in case of angles and crossings should be provided. Bitumen felt is capable of accommodating slight movements but cannot withstand heavy loads.

Sheets of lead, copper and aluminium (metal sheets)

These are used as membranes for damp proofing and are of flexible type.

Sheets of lead

The thickness of the sheet should be such that the weight of the sheet is not less than 20 kg/m2. These are spread on the walls and overlapped at the joints. The sheets of lead should be embedded in lime mortar and not in cement mortar (because cement chemically reacts with lead and destroys it). The surfaces of lead should be protected by a coating of bitumen against corrosion. DPC formed by lead sheet provides an impervious and highly resistant surface against lateral movements.

Sheets of copper (minimum 3 mm thick)

Like lead sheets, these are spread, lapped and jointed. They are embedded in lime or cement mortar. This is another excellent DPC material that possesses characteristics such as high durability, good resistance to dampness and high resistance against sliding action.

Sheets of aluminium

These can also be used for DPC but not as good as to lead or copper sheets. These sheets should be protected with a layer of bitumen.

Combination of sheets and bituminous felts

A lead foil is sandwiched between the sheets of asphalt or bituminous felt. This combined sheet is known as ‘lead core’ and DPC of this core possesses the characteristics of easy laying, durability, efficiency and economy.

Mastic asphalt

This is obtained by heating the asphalt with sand and mineral fillers. This is a semi-rigid material and forms an excellent impervious layer for damp proofing, i.e., DPC. However, it requires special care in its laying. Good mastic asphalt has many characteristics, such as high durability, excellent water-proofing quality and reasonable elasticity. This can withstand only very slight distortion and is liable to lateral movements under heavy pressures or very hot climates.

ALSO READ: Damp Proofing | Sources Of Dampness | Effects Of Dampness | Techniques And Methods | Uses

Bricks

Good dense bricks, which absorb water less than 4 per cent of their weight, are suitable as a DPC material at places where the damp is not excessive. The joints are left open. They are widely used for providing or inserting a DPC membrane in an existing wall.

Stones

Generally, dense and sound stones, such as granite, trap and slates, are laid in cement mortar in two courses to form an effective DPC. The stones are used for the full width of the wall. While laying the stones, care should be taken in breaking the continuity of vertical joints.

Cement concrete layers

A cement concrete layer, having mixed proportions 1:2:4 (1 cement:2 sand:4 aggregates) with waterproofing agents, is used as DPC at the plinth level. It is effective in stopping the water rising due to capillary action but allows the water to pass through the cracks, etc., and hence is suitable as DPC material where dampness is not in excess. The concrete layer is used as a horizontal main DPC in thickness varying from 4 to 15 cm followed by two coats of hot bitumen paint.

Mortar

It is used in two ways, either (i) as a bedding layer for taking up other types of DPC or (ii) as a waterproofing plaster. For the bedding layer, the mortar is prepared by mixing cement and sand in proportions 1:3 and adding slight lime to increase the workability. For waterproofing plasterwork, the mortar is prepared by mixing either of the following:

a. 1 cement:2 sand pulverized alum and soap water,

b. Cement: sand in proportions 1:3, with patented waterproofing material like pudio, dampro and sika. After applying this plaster in 2–4 cm thickness, it is painted with two coats of hot bitumen.