In this article we will discuss about:- 1. Manufacture of Common Tiles 2. Characteristics of a Good Tile 3. Types.
Manufacture of Common Tiles:
Following four distinct operations are involved in the general process of manufacturing the common tiles:
(i) Preparation of clay
Each of the above operation will now be briefly treated.
(i) Preparation of Clay:
The selected clay is taken and it is made free from any impurity such as grit, pebbles, etc. Such clay is then pressed and converted into fine powder in pug mills.
For tiles of superior quality, a large quantity of pure water is added to the powdered clay and it is well mixed in a tank. The mixture is then allowed to stand quietly. The coarse heavy particles settle at the bottom of tank. The fine particles are taken into other tanks and the water is then allowed to dry off. The fine clay left after such process is used for the manufacture of tiles.
To make the tiles hard and impervious, a mixture of ground glass and pottery-ware may be added in required quantity to the clay of tiles.
The clay is placed in moulds which represent the pattern or shape in which the tile is to be formed. The moulding may be done either with the help of wooden moulds or mechanical means or potter’s wheel.
The wooden moulds should be prepared from well-seasoned timber. The clay is pressed into such moulds and tiles are ready for drying when clay is taken out of moulds. The care should be taken to preserve the shape of tiles during the removal of moulds. The tiles which do not have a uniform section throughout their length are moulded with the help of wooden moulds.
The moulding with the help of mechanical means includes the provision of machines and the clay is pressed into such machines to get tiles of desired section and shape. This method of moulding is adopted for tiles having a uniform section throughout their length. The cutting of tiles in desired length is carried out with the help of a fine wire.
The method of moulding by potter’s wheel is similar to one that is adopted by a potter in the manufacture of earthenware vessels. This method is adopted when tile is of perfectly circular shape when on the wheel. It may however have diameter varying along its length.
The tiles, as they come out of moulds, are placed flat one above the other in suitable number. The different heaps are thus formed. After about 2 days, the irregularity of tiles due to warping is corrected with a flat wooden mallet. The tiles are then lifted as they have by now become hand-hard. The edges and under surfaces are cleaned. They are stacked on edge under a shade to dry for about two days or so. The drying under a shade prevents warping and cracking of tiles due to rain and sun.
The tiles are then burnt in kilns. A typical kiln, known as the Sialkote kiln, for accommodating about 30000 to 40000 tiles is shown in fig. 3-1. It is circular in shape and is protected by a shed. A layer of bricks is laid flat on the rows of long narrow flues. The burning is effected by firing wood placed in these flues. The bricks are arranged in such a way that open spaces are left in between them.
Above the layer of bricks, the dried tiles are placed on edge layer by layer. The closing of doorways is affected by brickwork in mud. The top of kiln is covered with a layer of old tiles placed in a loose condition.
The regulation of heat is important to achieve better results. The fire is gentle in the beginning. It removes moisture. It is then raised to about 800°C. It is slackened for a period of about 6 hours and again raised to white heat, temperature being 1300°C. This temperature is maintained steady for a period of 3 hours.
The process of slackening the fire for 6 hours and then raising the temperature to white heat is repeated. The white heat is maintained for 4 hours. Finally, the flues are filled with the fuel and the doorways are closed by brickwork in mud. The kiln is then gradually allowed to cool down. It requires about 72 hours to complete the process of burning the tiles.
The tiles are taken out of the kiln. The under burnt tiles are sorted out and they are placed on the top of kiln in the subsequent burning of tiles. It is thus seen that this kiln is an intermittent kiln.
A new automatic process known as the single firing technology has been found out and it has resulted in the drastic reduction of the firing cycle from 72 hours in the old double firing conventional method to a stunning average of just one hour.
This new technology has reduced the fuel consumption and lowered the total cost of production. The new technology has increased the quality, design and versality of tiles and thus a new chapter of discovery has opened for the ceramic industry.
Characteristics of a Good Tile:
Following are the characteristics of a good tile:
(i) It should be free from any cracks, flaws or bends.
(ii) It should be regular in shape and size.
(iii) It should be sound, hard and durable.
(iv) It should be well burnt.
(v) It should give a clear ringing sound when struck with hand or with one another or with light hammer.
(vi) It should fit in properly, when placed in position.
(vii) It should give an even and compact structure when seen on its broken surface.
(viii) It should possess uniform colour.
Types of Common Tiles:
Depending upon the use to which the tiles are put, the following are their different types:
(i) Drain tiles
(ii) Floor or paving tiles
(iii) Roof tiles.
(i) Drain Tiles:
These tiles are prepared in such a way that they retain porous texture after burning. Hence, when such tiles are laid in the water-logged areas, they allow subsoil water to pass through their skeleton. These drains may be circular, semi-circular or segmental. They are also used to convey irrigation water. Such drain tiles are rarely adopted in modern times.
(ii) Floor or Paving Tiles:
The floor or paving tiles may be square or hexagonal in shape. These are flat tiles and their thickness varies from 12 mm to 50 mm. The size of square tiles varies from 150 mm to 300 mm. The floor tiles should be hard and compact so that they can resist wear and tear in a better way. The floor tiles of thin section can be adopted for ceiling also.
To prepare coloured floor tiles, the colouring substance is added in the clay at the time of its preparation. The floor tiles of comparatively less strength can be adopted for fixing on walls.
The ceramics floor or paving tiles have the following distinct advantages despite their high cost:
(a) They are available in an endless range of colours and designs.
(b) They are easier to lay as they are small in size.
(c) They are much lighter than either mosaics or marbles.
(d) They are scratch, stain and damp-proof as well as anti-slip.
(e) They do not require polishing and the floor is ready for use the very next day.
(iii) Roof Tiles:
These tiles are used to serve as covering for pitched roof. The various types of roof tiles are available in the market.
Their important varieties are as follows:
(a) Allahabad Tiles:
These tiles are made from selected clay. The moulding of clay is done under pressure in machines. The burning of these tiles is done in such a way that they attain more strength. These tiles are provided with projections so that they interlock with each other, when placed in position. The tiles of special shapes are made for hip, ridge and valley portions of the roof. These tiles are extensively used in North-Western India.
(b) Corrugated Tiles:
These tiles have corrugations and when they are placed in position, a side lap of one or two corrugations is formed. The placing of such tiles on a roof gives an appearance of corrugated galvanized iron sheets. These tiles are handsome in appearance, but they can easily be blown away by a violent wind.
(c) Flat Tiles:
These are ordinary floor tiles. To fix them on battens, two or more holes are provided on their surface. The suitable laps are provided at sides and edges.
(d) Flemish Tiles:
These tiles have got the shape of letter ‘s’ with dimensions as 350 mm X 225 mm x 12 mm and they are prepared with the help of a mould. These tiles do not form a good covering as the plain tiles and they are used only for sheds.
(e) Guna Tiles:
These are hollow tapered burnt clay tiles. They are conical in shape with a base of 100 mm diameter at the broader end and 75 mm at the narrower end. The thickness of the annular ring is 6 mm. These tiles can be manufactured on the potter’s wheel and on account of their conical shape, they can be inserted one into another so as to form a ring of guna tiles. The ring may be made of suitable shape such as circular, elliptical, parabolic, etc.
(f) Manglore Tiles:
These tiles are of flat pattern and they are provided with suitable projections so that they interlock with each other, when placed in position. These tiles are red in colour and made of double channelled Basel Mission Manglore pattern. The special Manglore tiles are available for hip, ridge and valley portions of the roof. It is found that about fifteen Manglore tiles are required for covering one square metre of roof area.
These tiles are manufactured on large scale in South India especially at Manglore, Cochin and Calicut. This industry was established in the early 19th Century by German Missionaries. The first unit manufacturing Manglore pattern tiles was started at Morvi, Saurashtra in 1951 and at present, more than 200 units are working in this area.
Thus, Morvi has become the Bangaluru of Gujarat State and some other units, about 30 or more, are also located in Bulsar and Surat districts of the Gujarat State.
The Manglore pattern roofing tiles are becoming popular in rural and semi-urban areas and they are used by middle and low income group people because of various reasons such as architectural effect, scarcity and rising prices of other substitutes, growth of population, etc. The life of these roofing tiles is estimated at about 25 years with replacement of about 5% per year.
According to the Bureau of Indian Standards (BIS): 654-1962, the Manglore pattern tiles are divided into two classes, namely, Class AA and Class A.
The characteristics of both these classes are mentioned in table 3-1.
The dimensions of Manglore tiles are given in table 3-2.
(g) Pan Tiles:
These tiles are short and heavy. They are less curved in section than pot tiles. Such tiles are moulded flat first and then they are given the required curvature by moulding in suitable forms. The drying and burning of tiles are done carefully to get better quality of tiles. These tiles are of length 330 mm to 380 mm and of width 230 mm to 280 mm.
(h) Pot Tiles:
These are ordinary half round country tiles and they are also known as the locking tiles. They are prepared on potter’s wheel and shape is given to such tiles by a potter with his wet hands. The polishing of inner and outer surfaces is done either with a wet cloth or a wetted strip of leather.
These tiles are semi-circular in section and taper along the length of 300 mm with diameter of about 230 mm at larger end and of about 200 mm at smaller end. They are placed on the roof with their concave and convex sides uppermost alternatively so that they can become self-locked. An overlap of at least 80 mm is provided at edges, when these tiles are used.
These tiles are liable to break easily and hence they require frequent replacement and repair which may prove to be extremely difficult.
Following are the advantages of these tiles:
(i) These tiles are less liable to be displaced by the birds.
(ii) These tiles may be used as a sole covering to the roof.
(iii) The pitched roof may be made completely leak proof because of the fact that good drainage is ensured by these tiles even when the slope of roof is less.