Tiles ( Building Tiles) are thin slabs of brick earth, burnt in a kiln. These are very thinner than bricks and have a high tendency to crack and twist in drying and burning than normal bricks and are more responsible for breakage.
Therefore, great care is needed in their manufacture. They should be dried in the shade, burnt, and cooled gradually in specially made kilns.
Fig: Floor Tiles
2. Manufacture of Tiles
The manufacture of the common tiles contains the following operations:
a. Preparation of Clay:
1. The selected clay ( the best blue clay for tiles is generally found a few feet below brick earth) is made free from impurities such as grit, pebbles, etc.
2. The clay is ground into powder in crushing roller or mills and then thoroughly pugged. For the manufacture of superior tiles, the powdered clay is mixed with a large quantity of water in tanks, well stirred up and then the mixture is allowed to settle.
The heavier and coarse particles sink to the bottom of the tank and the finer particles runoff into the lower tank, where the mater is allowed to dry leaving the fine clay ready for mixing. The method is termed the blunging process.
3. To make the tiles hard and impervious, a mixture of ground glass and pottery ware may be added in the required quantity to the clay of titles.
The following three methods are utilized for the moulding of tiles:
1. Wooden Patterns:
The tiles which are non-uniform in section throughout their whole length are moulded in patterns ( made of well-seasoned wood ).
Flat cakes of clay are made and when partly dry, they are moulded, pressed and turned around a wooden pattern to give them the required shape.
2. Potter’s Wheel:
a. This method is similar to one that is adopted by a potter in the manufacture of earthenware vessels.
b. This method is adopted when the tile is perfectly circular in shape when on the wheel. It may have a diameter varying along its length.
3. Mechanical Method:
This method of moulding is considered for tiles having a uniform section across their length.
The pugged clay is manufactured by mechanical means through Openings/Orifices of needed shape and size. The moulded clay coming out from the Opening/Orifice is taken on a platform (wooden or iron) and the tiles are cut off to the needed length by means of wireframes.
c. Drying :
Two days after moulding, tiles are slightly beaten with a flat wooden mallet to correct the irregularity in sharpness due to wrapping.
On the next day, they are lifted up when hand-hard and the edges and under surfaces are scarped.
They are then placed on edge and left to dry for about 2 days under shade to prevent wrapping and cracking when they are ready for loading in the kiln.
The tiles are burnt in a typical kiln, known as Sialkot, it can accommodate 30000 to 40000 tiles. Such kilns are partly underground and are generally provided with a roof.
A layer of bricks is placed flat on rows of long narrow flues.
The burning is affected by firing wood placed in these flues.
The bricks are placed in such a way that open spaces are left between them. Above the layer of bricks, the dried tiles are placed on edge layer by layer, until the kiln is fully loaded with raw tiles.
The doorways are then closed with bricks in mud plaster and the top is covered with old tiles and ash.
The firing of the kiln begins and the fire is kept low till the gases are moving out. The temperature is then raised gradually till the inner portions of the flues become red hot ( at about 800’C).
It is then slackened for about 6 hours, raised again, till the flues are white-hot (at about 1300’C) and kept as such for about 3 hours. The fire is again slackened for 6 hours, then increased once more to white hot and kept steady for about 3 to 4 hours.
At last, the flues are added with fuel and doorways are closed by brickwork in mud. The kiln is then slowly permitted to cool down. The process of burning the tiles is completed in about 72 hours.
“Single firing technology”- a new automatic process, entails the following advantages:
1. Drastic reduction of the firings cycle from 72 hours to an average of just one hour.
2. Reduced fuel Consumption
3. Reduced total cost of production
4. Improved quality design etc of the burnt tiles.
3. Characteristics of a Good Tiles
A good tile should own the following characteristics:
1. It should possess uniform colour.
2. It should be properly burnt.
3. It should be free from cracks, flaws or bends.
4. It should be hard and Durable.
5. It should have proper shape and size.
6. When placed in position, it should fit well.
7. Its broken surface should exhibit an even and compact structure.
8. It should give a clear ringing sound when struck with a light hammer or with another tile.
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4. Types of Tiles
The tiles, according to their utilization, are classified into the following five types:
a. Roofing Tiles:
These types of tiles should be strong, durable and fully leakproof.
Although expensive at the first cost, they need less maintenance cost.
Roofing tiles may be common tiles, encaustic tiles, Mangalore tiles and country tiles. The commonly used roofing tiles are described below:
i. Flat Tiles:
These tiles are rectangular in shape and are of various dimensions. They are placed in cement or lime mortar. The different types of flat tiles are discussed below:
a. Slate Tiles:
The sizes available are: 60 cm x 30 cm x 15 mm and 50 cm x 25 cm 10 mm.
These tiles should be reasonably straight, of uniform colour, texture, free from veins, crack, fissures, white patches, etc.
The water absorption after 24 hours immersion in cold water should be a maximum of 21 % by weight.
b. Burnt Clay Flat Terracing tiles:
These tiles should be uniform in shape, size and be free from irregularities, (e.g bends, twists, cracks etc.)
The water absorption should not exceed 20% by weight.
The compressive strength should be more than 7.5 N/mm2.
ii. Pot Tiles or Country Tiles:
These tiles are also sometimes called Pan Tiles. They are hand moulded, First into a flat tile, then to the needed shape on a wooden pattern and burnt in a kiln after the process of drying.
These tiles are semi-circular. These are mostly used alone or sometimes with flat tiles.
These tiles are usually used as a sole covering to the roof.
These tiles are placed on sloped roofs along with the concave side up and have a longer end towards the ridge. Then another row of the same tiles with the convex side up and a small end towards the ridge is laid covering the adjoining edges of every pair of tiles below.
These types of tiles are mostly used in rural areas.
iii. Allahabad Tiles:
These tiles are of different shapes. They are usually placed side by side and joints are then covered with half-round tile.
They should absorb water less than 20 per cent by weight.
They are used for making good and pleasing roofs.
iv. Corrugated Tiles:
These tiles have corrugations and when they are placed in position, and aside lap of one or two corrugations is formed.
The placing of such tiles on a roof gives the appearance of corrugated galvanized iron sheets.
They are very good in appearance but can be easily blown away by a violent wind.
v. Mangalore Tiles:
These tiles are red in colour and made of double channelled basel mission mangalore pattern.
They are of flat pattern and are provided with suitable projections so that they can interlock with each other when placed in position.
These tiles are manufactured on large scale in South India especially in Mangalore, Cochin and Calicut.
The life of these tiles is about 25 years with a replacement of about 5% per year.
These tiles are made from the good earth and are specially shaped.
vi. Encaustic Tiles:
These tiles consist of three layers:
1. The face is a thin coat of pure clay of the colour required.
2. The body is of coarse clay; and
3. The back is formed within a thin layer of clay different from the body as it is to prevent warping.
4. These tiles are employed for decorative purposes.
b. Flooring Tiles:
These tiles are flat and usually square or rectangular in shape. These can be manufactured in any colour and of any geometrical shape.
They should give a ringing sound when stuck with each other.
They should absorb less water by less than 24% by their weight.
The fractured surface of the title should be clean, dense and sharp at the edges.
They should resist maximum resistance to impact.
Common sizes of flooring tiles are: 15 cm (Length) x 15 cm (width) x 18 mm (Thickness); 20 cm x 20 cm x 20 mm; 22.5 cm x 22.5 cm x 22 mm.
c. Wall Tiles:
These are similar to the floor tiles except for their design and degree of burning.
They are burnt comparatively at a low temperature, glazed and burnt again at a still lower temperature.
They can be made in different designs and colours and be built to any size.
These are used on the face work; to some extent on arches and for architectural ceilings etc.
d. Drain Tiles
These tiles are usually long curved sections of various shapes and sizes such as semi-circular, a segment of a circle or circular.
They are usually used for draining wastewater. If they are to be employed for carrying sewage, glazed tiles should be used.
e. Glazed earthenware Tiles
These tiles are of earthenware, having a top surface glazed and underside unglazed so that tile may adhere properly to the base.
These tiles are made in two sizes: 149 mm x 149 mm and 99 mm x 99 mm, having thicknesses of 5 mm, 6 mm and 7mm. The joint thickness is 1 mm.
They should not absorb more than 18 percent of water.
These tiles and associated fittings are generally used for finishing the surfaces of walls and floors of water closets, bathrooms, kitchens, hospitals etc. (where cleanliness is important)
5. Specification of Building Tiles
1. Dimensions and Tolerance:
Dimensions and tolerance for various building tiles are given below:
|Types of Tiles||Dimensions||Tolerance|
|Roofing Tiles||20 cm x 20 cm or|
20 cm x 10 cm or
15 cm x 15 cm
Thickness 15 mm or 20 mm
|± 5 cm for length and width|
± 2 cm for thickness
|Floor Tiles||15 cm x 15 cm x 1.5 cm|
15 cm x 15 cm x 2.0 cm
20 cm x 20 cm x 2.0 cm
20 cm x 20 cm x 2.5 cm
25 cm x 25 cm x 3.0 cm
|± 5 cm for length and width|
± 2 cm for thickness
|Terracing Tiles||Length : 25 cm to 15 cmin stages of 2.5 cm|
Width: 20cm to 10 cm in stages of 2.5 cm
Thickness: 20 mm and 15 mm
|± 2% for length|
± 2% for width
± 2% for thickness
2. General quality:
a. The Building tiles should be made from good clay of even texture.
b. They should be well Burnt.
c. They should be uniform in size and shape.
d. They should be free from irregularities such as bends, twists, cracks, etc.
3. Warpage test:
a. In the case of flooring tiles, warpage should not exceed 2% along the edges and 1.5% along the diagonal.
b. In the case of terracing tiles, maximum warpage should not exceed in any direction by 1 %.
4. Water absorbtion test:
Water absorption test for roofing, flooring and tracing tiles is carried out as follows:
a. Take six tiles and dry them in an oven at a temperature of 100°C to 110°C till they attain a constant weight and then cool.
b. Weight them and then immerse the dry specimen completely in clean water at 24°C to 30°C for 24 Hours.
c. Remove each specimen, wipe off the surface water carefully with a damp cloth and weigh the specimen within 3 minutes after removing the specimen of water.
% of water absorption = (W2-W1) x 100% / W1
W1 = weight of the dry specimen and
W2 = weight of the specimen after 24 hours immersion in cold water.
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