Dinusha: floors

Chapter 19 Floors

Floors are provided to divide a building into different levels for creating more accommodation one above the other within a certain limited space. The bottom floor near the ground is known as the ground floor and the other floors above it are termed as upper floors, like first floor and second floor. If there is any accommodation constructed below the natural ground level, it is known as basement and the floor provided in it is known as the basement floor.

A floor may consist of two main components:

A sub-floor that provides proper support to the floor covering and the superimposed loads carried on it.
A floor covering which provides a smooth, clean, impervious and durable surface.

19.1 FACTORS AFFECTING SELECTION OF FLOORINGS

Each type of floor has its own merits and there is not even a single type which can be suitably provided under all circumstances, and more so when floors have to serve different purposes in different types of building.

Initial cost: The cost of construction is very important in the selection of a type of floor. A floor covering of marbles, granite, special clay tiles, etc. is considered to be very expensive, whereas a flooring of cork, slate, vinyl tile, etc. is moderately expensive. The floors made of concrete and brick offer the cheapest type of floor construction. It should be ensured during the comparison of cost for different floors that the cost of both covering and sub-floor has been accounted for.
Appearance: Flooring should produce the desired colour effect and architectural beauty in conformity with its use in the building. Generally, flooring of terrazzo, tiles, marble and cement mortar provides a good appearance whereas the asphalt covering gives an ugly appearance.
Cleanliness: A floor should be non-absorbent and capable of being easily and effectively cleaned. All joints in flooring should be such as to offer a watertight surface. Moreover, greasy and oily substances should neither spoil the appearance nor have a destroying effect on the flooring materials.
Durability: The flooring material should offer sufficient resistance to wear and tear, temperature, chemical action, etc. so as to provide long life to the floors. From the durability point of view, flooring of marble, terrazzo, tiles and concrete is considered to be of the best type. Flooring of other materials such as linoleum, rubber, cork, bricks, wood blocks, etc. can be used where heavy floor traffic is not anticipated.
Damp-resistance: All the floors, especially ground floors, should offer sufficient resistance against dampness in buildings to ensure a healthy environment. Normally, floors of clay tiles, terrazzo, concrete, bricks, etc. are preferred for use where the floors are subjected to dampness.
Sound insulation: According to modern building concepts, a floor should neither create noise when used nor transmit noise. Sometimes, it is required that any movement on the top floors should not disturb the persons working on the other floors. Suitable flooring is provided which is somewhat noiseless when travelled over.
Thermal insulation: It should be possible for a building to maintain constant temperature or heat inside the building irrespective of the temperature changes outside. Thermal insulation is needed to reduce the demand of heating in winter and refrigeration in summer. It is important in the case of wooden floors where heat losses are considerable and in solid floors with heating pipes or cables where the heat losses at the edges of the floor slab can be higher. Floors of wood, cork, etc. are best suited for this purpose.
Smoothness: The floor covering should be of superior type as to exhibit a smooth and even surface. However, at the same time, it should not be too slippery which will otherwise endanger safe movements over it, particularly by old people and children.
Hardness: It is desirable to use good quality floor coverings, which do not give rise to any form of indentation marks, imprints, etc. when used for either supporting the loads or moving the loads over them. Normally, the hard surfaces rendered by concrete, marble, stone, etc. do not show any impressions, whereas the coverings like asphalt, cork, plastic, etc. do form marks on the surfaces when used in traffic.
Maintenance: It is always desired that the maintenance cost should be as low as possible. Generally, a covering of tiles, marble, terrazzo or concrete requires less maintenance cost as compared to the floors of wood blocks, cork, etc. It should, however, be noted that the repairing of a concrete surface is more difficult than the floorings of tiles, marbles, etc.

19.2 TYPES OF FLOOR

The various types of floor commonly used are as follows.

19.2.1 Basement or ground timber floor

Timber floors are constructed on ground floors, generally in theatres. Several sleeper walls or dwarf walls of half brick thickness or full brick thickness are constructed at an interval of 1.5 m to support the timber floor. Wall plates are placed on walls and sleeper walls to support the joists supporting the floors. The joists are provided at a distance of about 30 cm and the timber planks are closely fitted over the joists to provide the floor. The arrangement for proper air circulation is made in the floor, otherwise timber will be attacked by dry rot. The following precautions are recommended:

Well-seasoned timber should be used in the construction of such floors.
Plain cement concrete 1:2:4 of 10 cm thickness is to be provided over the soil beneath the timber floor.
The empty space between the floor and the concrete base should be filled up with sand.
The damp proofing courses are to be placed in the external walls and at the top of the sleeper walls.

19.2.2 Single joist timber floor

This type of floor is used for residential buildings where spans are comparatively small and the loads are lighter. The wooden joists are placed at about 30 cm centre to centre, spanning the rooms in the shorter direction. Wooden planks are laid over these joists. The timber joists are supported on wall plates. Corbels may be required to support the joists if the width of the wall is not sufficient. Joists must be strong enough to withstand the loads and at the same time they should not deflect too much. If the length of the joist is more than 3.5 m, then struts are provided in the joists to check side buckling. The wooden planks are about 4 cm thick and 10–15 cm wide.

19.2.2.1 Advantages

Single joist timber floors are simple to construct.
They require less initial cost.
Distribution of loads on the wall is more uniform as the joists are spaced closely.

19.2.2.2 Disadvantages

The joists may sag and, hence, cracks will develop in the ceilings.
They are not soundproof.
Deep joists are required for larger spans that increase the weight and construction cost of the floor.
The loads are transmitted to the openings such as windows or door lintels because of evenly spaced joists.

19.2.3 Double joist timber floor

This type of floor is stronger than the single joist timber floor. They are used for longer spans of 3.6–7.5 m and prevent the travel of sound waves to a great extent. Intermediate supports called binders are placed for bridging the joists. Binders are spaced at a centre-to-centre distance of about 2 m. The ends of binders are kept on wooden or stone blocks and they should not be embedded in the masonry wall. The ceilings may be fixed to the bottom of the binders by fixing a ceiling joist to the binders. Lathing is fixed to the ceiling joist.

19.2.3.1 Advantages

The loads are transmitted to the wall at certain specified points and, hence, door and window openings may be avoided.
This is a more rigid type of flooring and, hence, there is less chance of developing cracks in the plastered ceiling.
It is more soundproof.
The use of additional binders near the walls can eliminate the need of wall plates.

19.2.3.2 Disadvantages

More labour is required
The depth of the floor is considerably increased and, thus, the head room is reduced

19.2.4 Framed timber floor

This type of timber floor is used for spans of more than 7.5 m. Girders are placed between the walls and the binders are put on the girders and the bridging joists rest on the binders. The spacing between girders depends on the type and size of the girder and the size of the binders. The ends of girders are put on stone or concrete templates in the wall. The ceilings are fixed directly to the binders or ceiling joists may be employed.

19.2.5 Filler joist floor

Small sections of rolled steel joists are encased in the concrete. The joist is supported on walls or on steel beams. The joists are placed at a centre-to-centre distance of 60–90 cm and act as reinforcement in the concrete. The rolled steel joists and beams should be completely encased in the concrete.

19.2.6 Jack arch floor

Bricks or concrete may be used for the construction of jack arch floor. The arches are provided between the lower flanges of rolled steel joists at a centre distance of not more than 1.5 m. The rise of the arch is generally one-twelfth of the span. Mild steel ties are provided in the end spans to take up the tension developed due to the arch action of the floor. The diameter of tie rods is 18–25 mm and their spacing is 1.8–2.4 m. In addition, they are rigidly fixed on the walls, the side filling is done by lime concrete and the desired floor covering is provided. Plain ceiling is not obtained in this case and it may be considered as a shortcoming of such construction.

19.2.7 Double flagstone floor

For spans less than 4 m only rolled steel joists are placed, but if the span exceeds 4 m, a framework of rolled steel beams and joists is formed. Flagstones of about 40 mm thickness and proper width are placed on the lower flanges and upper flanges. The joints of flagstones in the top layer are given a fine finish for improved appearance. The empty space is filled up with selected earth.

19.2.8 RCC floor

Reinforced cement concrete (RCC) slab is being more commonly used in the construction of modern buildings. For small spans and comparatively lighter loads, a simple RCC slab is suitable. If the ratio of the length and width of a room is more than 1.5, the slab is designed to span along the shorter direction. The main reinforcement is provided along this shorter dimension of the room. The thickness of the slab is guided by the superimposed loads, span and type of concrete used. The end of the slab rests on the wall. When the building is constructed in reinforced concrete frames, it is essential to construct the slab monolithic with the supporting beams. For larger spans and greater loads, RCC beams and slab construction are adopted in the construction of buildings. The slab acts as a flange of the beam and is cast monolithic with the beams. In this case, the size of the beam is greatly reduced. Over the RCC floor suitable covering is laid to get the desired finish.

19.2.9 Flat slab floor

It is directly supported on the columns without providing any intermediate beams. This type of construction is adopted when the use of beams is forbidden.

19.2.9.1 Advantages

More clear head room is available for use.
Even for quite heavy loads, thinner slabs are required.
No projecting of beams is to be seen and, therefore, the need of false ceiling is eliminated.
It is convenient to make lighting arrangements.
The framework and construction of flat slabs are simpler.

Flat slabs are commonly used in commercial buildings, factories and warehouses, etc., but they are not economical for lighter loads.

19.2.10 Hollow tiled ribbed floor

To reduce the weight of a solid floor structure, a hollow tiled ribbed floor is constructed. In this type of construction, hollow blocks of clay or concrete are used. These hollow bricks or tiles are placed at about 10 cm apart. In this space of 10 cm, mild steel bars of 8–12 mm diameter are placed. The surfaces of the hollow tiles are kept rough to develop a better bond with the surrounding concrete. A minimum cover of 8 cm is provided at the top of the tiles. The empty spaces are filled up with concrete. These floors are fireproof, soundproof, damp proof, light and economical. A properly designed floor of this type can carry considerably heavy loads.

19.3 FLOOR COVERING

Floor coverings are provided to improve the appearance, cleanliness, noiselessness and damp proofing. Various types of materials are used and different treatments are done. The following types of floor coverings are generally employed.

19.3.1 Mud flooring

This is mainly used in unimportant buildings, particularly in the villages. They are cheap, hard, fairly impervious and easy in construction and maintenance. Thermal insulation properties are also very high. To prepare this a 25-cm thick layer of selected moist earth is spread over a prepared bed and rammed well to get a consolidated layer of 15 cm thickness.

19.3.2 Brick floor covering

It is employed for cheap constructions such as godowns, sheds, stores and barracks and where good bricks are available. Over well-compacted and levelled ground a layer of lean cement concrete mix (1:6:18) of 10 cm thickness is laid. Over this bedding, bricks are placed in proper bonds on their edges. They are joined with cement or lime mortar. Sometimes, the joints are pointed to obtain a better appearance. The only drawback of brick floor covering is that it absorbs water.

19.3.2.1 Merits

It offers a durable and sufficiently hard floor surface.
It provides a non-slippery and fire-resistant surface.
It is cheaper in initial cost as compared to cement concrete, mosaic and terrazzo flooring.
It is easy to maintain.

19.3.2.2 Demerit

This type of flooring acts as an absorbent

19.3.3 Stone floor covering

Square or rectangular slabs of stones are used as the floor covering. Generally, 20–40 mm thick stone slabs of size 30 cm × 30 cm, 45 cm × 45 cm, 60 cm × 60 cm, 45 cm × 60 cm, etc. are used. The stone should be hard, durable, tough and of good quality. The earthen base is levelled, compacted and watered. On this surface a layer of 10–15 cm thick concrete is laid and properly rammed. Over this concrete bed the stone slabs are fixed with a thin layer of mortar. Before fixing the stone slabs in position, they are dressed on all the edges and the joints are finished with cement. The stone surface may be rough or polished. A rough surface is provided in rough works like godowns, sheds, stores, etc. and a polished surface is provided in superior type of works. A slope of 1:40 should be provided in such type of floor covering for proper drainage.

19.3.4 Concrete floor covering

The concrete flooring consists of two layers:

A base course or the subgrade and
A wearing course

The concrete flooring consists of a topping of cement concrete 2.5–4 cm thick laid on a 10–15 cm thick base of either lime or cement concrete. The actual construction operation consists of:

Ground preparation
Formation of base course
Laying of topping concrete
Laying of wearing coat
Grinding and polishing and
Curing

19.3.4.1 Merits

It is non-absorbent and, hence, offers sufficient resistance to dampness. This is used for water-retaining floors as well as stores.
It possesses high durability and, hence, is employed for floors in kitchens, bathrooms, schools, hospitals, etc.
It provides a smooth, hard, even and pleasing surface.
It can be easily cleaned and overall has proved economical due to less maintenance cost.
Concrete being a non-combustible material offers a fire-resistant floor required for fire-hazardous buildings.

19.3.4.2 Demerits

Defects once developed in concrete floors, whether due to poor workmanship or materials, cannot be easily rectified.
The concrete flooring cannot be satisfactorily repaired by patchwork.
It does not possess very satisfactory insulation properties against sound and heat.

19.3.5 Tiled floor covering

Clay tiles of different sizes, shapes, thickness and colours are prepared and they are used as floor coverings. They are placed in position on a concrete base with a thin layer of mortar. When these tiles are to be fixed on timber floors, special beds of emulsified asphalt and Portland cement are used.

19.3.5.1 Merits

It provides a non-absorbent, decorative and durable floor surface.
It permits quick installation or laying of floors.
It is easily repaired in patches.

19.3.5.2 Demerits

It is generally costly in initial cost as well as in maintenance cost.
On becoming wet, it provides a slippery surface.

Vitrified tiles

Vitrified tiles have zero water absorption property. They resemble granite but offer a great variety in terms of finish, colour and design options. Polished vitrified tiles such as mirror stone, granamite and marbogranite are cheaper than marble and granite.

Ceramic tiles

Ceramic tiles are non-slippery and are used in wet areas like bathrooms and kitchens. They are available in a variety of interesting shapes, wide range of colours and textures. They are used in living rooms also. Ceramic tiles are usually embedded in mortar. Special tile adhesives and tile grouts are also available which allow easy laying and render the tiled area useable within 24 hours.

Laying of tiles

Use a waterproof, floor tile adhesive which allows slight flexibility when set. Follow the manufacturer's instruction and use a notched or plain trowel, as directed, to spread the adhesive on the floor over a manageable area for laying approximately 10 tiles.

Use a layer of adhesive on the back of the tile and press into the desired position. It is very important to lay the first tile correctly, as its position will determine the position of all the other tiles in the room. Use a batten nailed to the floor to give a straight edge to guide the positioning of the tiles. Remember to use plastic spacers or a thick card to regulate the distance between the tiles. These areas will be grouted when the floor is complete and must be equally spaced for neat, accurate results.

Use a spirit level to check the horizontal level and a straight edge to continually check the position of the tiles on the floor. Continue across the room and work towards the door. Leave the room for 24 hours. Then remove the battens and cut the border tiles and fix in a similar way. Remove the plastic spacers or thick card and grout the tiles.

Grout is available in a variety of colours, but the standard colours are white, grey or brown. However, most floor tiles are grouted with a mortar mix. Use a plastic scraper or a rubber blade to push the grout between the gaps in the tiles. Make sure all the spaces are evenly filled and then wipe the grout off the tile surface before it dries. Use a blunt edge of a stick or tool carefully to smooth the surface of the grout in the gaps, but do not ‘dig down’ into the grout. Remove any excess grout before it dries. Allow the floor to dry completely before polishing the surface of the tiles with a dry cloth.

19.3.6 Wooden floor covering

This type of floor covering is the oldest type, but nowadays it is used for some special-purpose floors such as theatres and hospitals. It possesses natural beauty and has enough resistance to wearing. Wooden floor covering may be carried out in one of the following three types:

Strip floor covering: This is made up of narrow and thin strips of timber which are joined to each other by tongue and groove joints.
Planked floor covering: In this type of construction, wider planks are employed and these are joined by tongue and groove joints.
Wood block floor covering: It consists of wooden blocks which are laid in suitable designs over a concrete base. The thickness of a block is 20–40 mm and its size varies from 20 × 8 to 30 × 8 cm. The blocks are properly joined together with the ends of the grains exposed.

19.3.7 Mosaic floor covering

This type of floor covering is commonly used in operation theatres, temples, bathrooms, etc. A concrete base is constructed for laying the floor covering. Over this base lime or cement mortar is placed to a depth of about 2 cm and it is levelled up. A layer of cementing material about 3 mm in thickness is spread. The cementing material consists of two parts of slaked lime, one part of powdered marble and one part of pozzolana. After 4 hours of laying this cementing material, a mixture of coloured cement and chips are laid. This surface is left for 24 hours and then it is rubbed with pumice stone to get a smooth and polished surface. The polished surface is left for about 2 weeks before use.

19.3.8 Rubber floor covering

It consists of pure rubber mixed with cotton fibre, granulated cork or asbestos fibre and the desired colouring pigments. A small amount of sulphur is also added. Its thickness varies from 3 to 10 mm and it is available in many designs and patterns. It is available in the form of tiles or sheets and can be directly laid over the floor by the vulcanizing process. It is mostly used in hospitals, radio stations, etc. The flooring is elastic, attractive, comparatively warm and soft.

19.3.9 Linoleum floor covering

It is the fabricated form of a mixture of resins, linseed oil, gums, pigments, wood flour, cork dust and other filler materials. It is available in the market in rolls of width about 2–4 m. The thickness varies from 2 to 6 mm. These tiles are also manufactured in various sizes, shapes and patterns. This floor covering is laid over an effective damp-proof course. It is cheap, durable, attractive, comfortable and moderately warm. It can be cleaned easily.

19.3.9.1 Merits

It provides an attractive, resilient durable and cheap surface.
It offers a surface that can be easily washed and cleaned.
Being moderately warm with cushioning effect, it provides comfortable living and working conditions.
It offers adequate insulation against noise and heat.

19.3.9.2 Demerits

It is subjected to rotting when kept wet for sufficient time and its use is not recommended for basements.
It does not offer resistance against fire, being combustible in nature.
This covering when applied over a wooden base may get torn under excessive sub-floor movements.

19.3.10 Glass floor covering

It is used when it is desired to admit light to the floor below. Structural glass is available in the form of slabs or tiles. They are fitted within frames of different types. The members of the frame are closely spaced such that the glass floor covering can take up the superimposed loads without breaking. This type of floor covering is not commonly used.

19.3.11 Magnesite floor covering

It is known as composite flooring or jointless flooring. It is composed of a dry mixture of magnesium oxide, a pigment and inert filler materials, e.g., wood flour, asbestos or sawdust. Liquid magnesium chloride is mixed to this powder and a plastic material is obtained in situ. This plastic material is laid over the floor and the surface is levelled with a trowel. It can be directly laid over stone, concrete or wooden floor base. It is cheap and is used as floor covering for office buildings, schools, factories, etc.

19.3.12 Plastic floor covering

Thermoplastic tiles can be economically used as floor covering on the concrete floor base. It is generally not laid on a wooden floor base as the preparation of the wooden surface for receiving the tiles is very costly. Plastic floor covering has been used with success in all types of buildings like offices, hospitals, shops, schools and residential buildings.

19.3.13 Terrazzo floor covering

Terrazzo is a mixture of cement and marble chips and the surface is polished with carborundum stone to obtain a smooth finish at the top. The base for this type of floor covering is concrete and is laid in the ordinary way. On the 3 cm concrete (1:3) base, a thin layer of sand is sprinkled evenly and it is covered by tarred paper. A layer of rich mortar is spread over it and then terrazzo mixture is placed over it evenly. Marble chips of 3–6 mm are mixed with white or coloured cement in the proportion 1:2 or 1:3 to get the terrazzo mixture. Dividing strips of metal, 20 gauges thick, are inserted into the mortar base to form the desired pattern and in these small bays the terrazzo mixture is laid alternatively. The terrazzo is levelled in position by a trowel. If required some additional chips are also added at the surfaces so that about 70 per cent of the surface area is covered by the marble chips.

When the terrazzo has hardened, the surface is rubbed by coarse and fine carborundum stones, respectively, to get a smooth finished surface. It is kept wet with water while rubbing. The surface is cleaned with water and soap solution and then ax polish is applied to the surface. This type of floor covering is very costly and is used to obtain a clean, attractive and durable surface in public buildings, hospitals bathrooms, etc.

19.3.14 Marble and granite flooring

Naturally available stones like marble and granite are used as flooring materials. They are available in the form of flat slabs and can be laid above the prepared concrete base. Marble slab is to be polished with carborundum stone, whereas granite does not require any polishing. Their hardness, durability and aesthetic appearance have increased its demand as a flooring material.

REVIEW QUESTIONS

What is the main function of a floor and what are its main components?
What are the factors affecting selection of floors?
Briefly discuss the different types of floors.
What are the advantages of flat slab floors?
What is the necessity of floor coverings?
Briefly explain the different types of floor coverings.
Briefly discuss RCC flooring.
Write short notes on
1. Wooden floor covering
2. Mosaic floor covering
3. Glass floor covering
4. Granite flooring