23

GROUND AND UPPER FLOORS

23.1 INTRODUCTION

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 ground floor. The construction below the ground level or the building has basement, the floor is termed as 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 the full support from the ground. The major problems of upper floors are the strength and stability.

23.2 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:

1. Strength and stability
2. Damp prevention
3. Heat insulation
4. Sound insulation
5. Fire resistance
6. Durability

23.3 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.

23.3.1 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:

1. Initial cost
2. Appearance
3. Durability
4. Cleanliness
5. Thermal insulation
6. Dampness
7. Indentation
8. Noiselessness
9. Maintenance
10. Fire resistance

23.3.2 Upper Floors

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

1. Initial cost
2. Floor loads
3. Type of construction
4. Plan of the building
5. Function of the building
6. Fire resistance
7. Sound insulation
8. Type of ceiling
9. Wearing surface
10. Weight and position of floors

23.3.3 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. Selection of basement floors depends on the following factors:

1. Initial cost
2. Availability of ventilation
3. Drainage of water from the floor
4. Adequate safety against fire
5. Ground water level

23.4 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, terrazo tiles, marbles, stones, mosaic, wood, etc.

23.4.1 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 of 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. 23.1:

1. 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.
2. Intermediate slabs are placed from both the sides taking care that the tops of stone slabs are touching the string which ensures the provision of proper grade.
3. All stone slabs should be of uniform thickness, strength and well drained on edges for residential and public buildings.
4. Width of joints between the slabs should not exceed 0.5 cm.
5. Rough surface stone, may be used for godown, sheds, stores, etc.

Figure 23.1 Stone flooring

23.4.2 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 herring bone 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. 23.2:

1. An excavation of about 40 cm depth below the intended level of the floor is made.
2. The earth surface is levelled, watered and well rimmed until it is dry and hard.
3. Over the earth, above a sub-grade of 25 cm depth consisting of rubble or brickbats is laid.
4. Over this, a 10–15 cm thick layer of lime concrete or lean cement concrete (1:3:6) is laid.
5. Upon this prepared sub-grade, bricks are laid in the desired shape.

Figure 23.2 Brick flooring

23.4.3 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 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:

1. The wearing surface is susceptible for damage due to subsequent floor use.
2. As the base course if undergoing only small settlement immediately, there is a possibility for hair cracks.
3. Repairing the damaged top surface is difficult.
4. 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 base course. The floor finish generally used is ordinary concrete finish of 1: : 3 (Fig. 23.3). Under controlled conditions, a mix of 1:2:4 ratio with carefully selected aggregates may be used.

Figure 23.3 Concrete flooring

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.

23.4.4 Granolithic Floors

It is a concrete flooring with a different type of floor finish called granolithic. Granolithic finish is a concrete made of special selected aggregate. The thickness of 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 suitable for coarse aggregate. In order to get a better granolithic finish, 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.

23.4.5 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 terrazo finish is laid over the concrete base course (as explained in concrete flooring) by two methods.

1. 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.
2. 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 terrazo mix (1 cement: 3 marble chips) of 6 and 12 mm is laid after adding water and making workable mix.

After curing for several days, the surface is polished by means of grinding machine fitted with 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 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.

23.4.6 Mosaic Floors

For 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 pattern. 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 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.

23.4.7 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. 23.4).

Figure 23.4 Tiled flooring

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

23.4.8 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 school, 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.

23.4.9 Marble Floors

High quality marble slabs in the required sizes and colours are available in the market. The construction procedure is same as that of mosaic flooring except 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 other superior type of works. Now-a-days some quality marbles are used for residential buildings also.

23.4.10 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 jointed to each others 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. 23.5.

Figure 23.5 Wooden block type timber flooring

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.

23.5 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.

23.5.1 Timber Floors

Timber floors are used only in areas where more timber is available at 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 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 ceiling. Further long joists need strutting to avoid buckling. The planking consists of wooden boards of 4 cm thickness and 10–15 cm wide. Figure 23.6 shows the details of single joist timber floor, and the details of the joist’s joint is shown separately.

Figure 23.6 Details of single-joint timber floor

23.5.2 Jack Arch Brick Floors

Bricks and plain concrete can not be used directly as 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. 23.7. The rods are encased in the wall along with a 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 centering ahead. This operation is continued till the work is completed.

Figure 23.7 Brick jack arch floor

23.5.3 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. 23.8).

Figure 23.8 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:

1. A centring of steel or timber is erected to support its own weight and the super-imposed load.
2. The reinforcement is placed on the centring before coating a thin layer (2–5 cm) of cement concrete.
3. The required mix of cement concrete is then prepared and poured around the reinforcement up to the required thickness of the slab.
4. The concrete is well consolidated by ramming or using a vibrator.
5. The concrete is cured for a minimum period of 2 weeks to attain its full strength.
6. After concrete has sufficiently hardened, the formwork is recovered.
7. The upper and lower surfaces of the slab are plastered and required finish are given.

23.5.4 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 the important buildings (Fig. 23.8).

23.5.5 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 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 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. 23.9).

Figure 23.9 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.

23.5.6 Flat Slab Floors

This type of floor is called as 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 head room restriction. The columns supporting the floor are invariably circular in cross-section and tops of the column are flared or tapered, which is called as capital. Sometimes certain portion of the slab, symmetrical with the column, is thickened which is called drop panel (Fig. 23.10).

Figure 23.10 Flat slab floor

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

1. As there is no projection of beam, there is no need for additional ceiling.
2. More clean head room is available.
3. Better ventilation and lighting is available.
4. Even for heavier loads only thin slab thickness is needed.
5. The construction is comparatively easier.

The flat slab floors are preferred under the following conditions:

1. When large equal number of panels are required.
2. Where clear large spans are required.
3. Where there is limitation in head room.
4. The ratio of length to breadth of panels is to be more than 4 : 3.
5. 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.

23.5.7 Resilient Floors

Floors made from materials such as PVC, linoleum, rubber, etc., are called resilient floors. Resilient floors are sound proof and dust free and are used in libraries, offices, computer rooms, show room, 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 polymer 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.

23.5.8 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. 23.11). 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.

Figure 23.11 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.

1. Floors are the horizontal units of a building structure which divide the building into different levels.
2. The floor of a building immediately above the ground is known as ground floor. The top portion of a ceiling forms the first floor or an upper floor.
3. The construction below the ground level or the building has basement, the floor is termed as basement floor.
4. The major problems of ground and basement floors are dampers removal and protection from heat.
5. 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.
6. 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.
7. The functional requirement of floors in general are:

   (i) Strength and stability

   (ii) Damp prevention

   (iii) Heat insulation

   (iv) Sound insulation

   (v) Fire resistance

   (vi) Durability

8. Factors to be considered for the ground floor selection are as follows:

   (i) Initial cost

   (ii) Appearance

   (iii) Durability

   (iv) Cleanliness

   (v) Thermal insulation

   (vi) Dampers

   (vii) Indentation

   (viii) Noiselessness

   (ix) Maintenance

   (x) Fire resistance

9. Factors to be considered for the selection of upper floors are as follows:

   (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

10. Types of ground floors are: stone floors, brick floors, concrete floors, granolithic floors, terrazo floors, mosaic floors, tiled floors, asphalt floors, marble floors and timber floors.
11. Types of upper floors are: timber floors, Jack Arch brick floors, RCC slab floors, RCC beam and slab floors, RCC T-beam slab floors, flat slab floors, resilient floors and hollow block rib floors.

1. Mention the factors to be considered in the selection of ground floors.
2. What factors you would consider while selecting an upper floor?
3. In what situations would you use stone floors?
4. A room 4 m × 5 m is to be covered by a wooden flooring. Describe the procedure to be followed.
5. Explain the construction procedure of a concrete floor giving its relative merits and demerits.
6. Under what circumstances cement concrete flooring is recommended.
7. Describe how a marble floor is laid with ordinary mortar joints.
8. How timber floors are used for ground floor and for upper floor?
9. Distinguish between granolithic and terrazo floors.
10. How a flat slab floor is constructed? Bring out the advantages of the same.
11. Describe four commonly adopted type of floorings that are recommended in modern buildings giving their merits and demerits.
12. What are resilient floors? Discuss.
13. Explain hollow block and rib floor.
14. Name the various types of floor construction suitable for the upper floors of a building.
15. What are the flooring materials you would recommend for the structures given below? Justify your recommendation.

    (i) Hospital

    (ii) Art Gallery

    (iii) Bathroom

    (iv) Hotel

    (v) School Building

    (vi) Bus Shelter