2. Introduction
Definition: These are Structural units moulded from clays in suitable shapes and burnt to
vitrification temperatures these differ from ordinary bricks in
• Dimensions
• Shape
• Degree of burning
These have been used throughout the world in a number of situations in building as Drains,
for flooring, for partition walls, and for roofing. They are invariably thinner than bricks used
for similar purposes.
• Manufacture of tiles: Tiles are manufactured by methods that are similar in all
respect to those for making bricks. The different stages in the manufacturing of tiles
are explained below:
• Preparation of clay
• Moulding
• Drying
• Burning
4. Stage I – Preparation Of Clay
• Only those clay which are sufficiently plastic are suitable for making tiles. These
clay generally occur in the lower layers of the brick clays.
• The Tile clays are extracted and cleared from fragments, pebbles and organic
matter if any. These are then grounded or Crushed to a fine powder using even mills
for crushing. It is common practice to add a mixture of finely ground glass and broken
pottery at the crushing stage to increase imperviousness and strength of tile.
• For ordinary type of tiles, the powdered clay is rendered into a homogeneous mix
using a Pugg Mill in a matter similar for brick making.
• For superior type of tiles, the crushed and powdered clays is rendered into
homogeneous mix using a pug mill in a matter similar for brick making for
superior types of tiles, however, the crushed and powdered clay are thoroughly stirred
in a tank, coarse clay particles are allowed to settle in tank, water consists fine clay
particles in suspended is separated and allowed to settle at a very slow rate.
• This finest clay is suitable for manufacture of delicate type of decorative tiles.
6. Stage II – Moulding
There are three different methods by which tiles are moulded. Selection of method
would depend on the shape and the size of the tile to be moulded.
1) Wooden Pattern Method: It is Similar to ground moulding of bricks manual
method, this method requires skilled moulder. Wooden pattern of required shape
and size is made from seasoned wood. Ash is spread on the inner side of mould.
Lumps of pugged clay is thrown into it by moulder and surplus clay is removed
by a wire string. Tile is removed from pattern by applying pressure with fingers and
thumb. This method is suitable for flat tiles, of non-uniform dimensions, &
non-circular shapes.
2) Potter’s Wheel Method: This is also a Manual method, and is best suited for
moulding circular tiles with uniform or varying diameter. In this method , the use
is made of potter wheel on which a skilled Labourer moulds tiles of required shape
from the pugged clays using the same techniques as for moulding pitchers & other
earthenware on the potter’s wheel. The moulder makes deep cut on either side on
the finally moulded pipe of clay before removing from the wheel. This cut helps
splitting of two halves easily after burning.
9. Stage II – Moulding / Stage III – Drying
3) Moulding by machines: For large scale manufacturing of tiles, for having uniform
sections machine moulding is adopted. Clay of suitable consistency is fed into
machine and pressed forward. It comes out from a die of required cross section in
the form of a continuous band and ribbon. Suitable lengths are then cut from clay
band and taken for drying.
• Stage III – Drying: Tiles Require greater care in drying them for two reasons;
a) As tiles are thinner, they are easily deformed if they handled carelessly .
b) Non Uniform drying may result in warping and cracking .
To over come these difficulties, Tiles are collected and arranged in heaps near the place of
moulding till they are hand-hard. Small deformations due to careless handling or due to
drying are corrected by using a flat wooden pallet. Thereafter the tiles are Placed for full
drying under a shed, which protects them them from direct direct sun and rain . Position of tiles
should be changed to get uniform exposure at all areas during drying period. Further, Any
pebbles or grit should be cleaned in the semi-dry stage of tile, otherwise once tile becomes hard,
such material will disfigure the tile on burning.
12. Stage IV – Burning
• When required in small number, tiles can be burnt in brick kilns. In that case, they are placed on the edge in
the upper part of the kiln over and above the last rows of the bricks. Generally two or three rows of tiles are
burnt in a brick kiln. Very often it may be only a tile- making unit. In that case the tiles are burnt in specially
designed intermittent type kiln called Sialkot kilns.
• A Typical Sialkot Kiln - Intermittent Type
• Consists of: a) Outer wall – made of bricks of suitable thickness The walls have two openings (i) doors for loading
and unloading of tiles (ii) doors for filling up fuels
b) The floor – which is divided into longitudinal, narrow channels at regular
intervals, which are known as the flues.
c) The roof – Which is supported on posts covering the entire area of the kiln
• The Burning of a batches of 30000 to 50000 tiles are carried out in the following manner.
• Steps:
• First Step - The Flues are filled with fuel and Covered by a layer of burnt bricks that are laid flat with
sufficient space in between to allow heat to pass upwards.
• Second Step -Tiles are stacked over the brick layer edge wise with space in between to the full kiln height a
Layer of ash and old broken tiles is laid at top to conserve heat
15. Stage IV – Burning
• Third Step – Once the kiln is loaded as above, Doors are closed by bricks laid in mud mortar.
• Fourth Step – Kiln is fired by igniting fuel in the flues the firing is continued for about 72 hours during which
time temperature is increased or decreased in accordance with the following scheme
• Time temperature scheme:
i. Gentle fire to begin – to dehydrate or remove any moisture from the tiles
ii. Fire increased around 800⁰ C – Red-heat for baking of tiles for 4 hours
iii. Fire is slackened – for 6 hours to allow the baked tiles a time to adjust to a temperature shock
iv. Fire is increased once again around 1300 ⁰ C – White-heat for 3 hours to convert baked tiles into vitrified tiles
v. Fire is slackened – for a second time for about 6 hours
vi. Fire is increased to a second white heat period – for 4 hours
vii. The flues are filled with fuel for the last time and closed from outside with brick in mud mortar.
viii. The kiln is allowed to cool very gradually before emptying.
• For burning of one batch of tiles - twice the white heat temperatures with two intervening periods of slackened heating.
• Regulating temperature – Most important aspect of tile burning
16. Characteristics Of Good Tiles
• Uniform Colour
• Properly Burnt
• Free From Cracks, Flaws, Bends
• Hard And Durable
• Proper Shape And Size
• Even And Compact Structure
• Clear Ringing Sound
18. Clay Floor Tiles
• As the name signifies these tiles are Used for
flooring in a building.
• These tiles are Flat in shape – rectangular,
square, other geometrical outline They come in
different
• Dimensions , more common being – 20 x 20 x 2
cm, 15 x 15 x 1.8 cm, 22.5 x 22.5 x 2.2 cm
• The required Qualities of flooring tiles are :
• Hard to resist wear, strong to resist loads
• Well burnt, give ringing sound while struck with each
other
• No visible foreign material like pebbles, grit, lime or
other fragments on surface or sides
• Dimensional specifications with tolerance of ±3 mm
for length or width, ±1.5 mm for thickness
• Uniform texture throughout the body
19. Clay Roofing Tiles
• They are Used as alternatives to corrugated and
plain Galvanized Iron Sheets and timber as roofing
material for building construction – especially
sloping roofs
• Qualities:
• Absolutely leak proof
• Very durable
• Easy to fix on the roof
• Less maintenance cost
• Types of roofing tiles:
1. Pot tiles
2. Flat tiles
3. Allahabad tiles
4. Mangalore tiles
5. Corrugated tiles
20. Pot Tiles
• It is Ordinary but common class of roofing
tiles.
• The individual tile is Semi-circular in
outline and has tappering Diameter: 15 cm
at one end 10 cm at other end
The Length of such tiles is : 20 to 25 cm and
Thickness: 1.5 to 2 cm they come in width
of 20 and 25 cm They are also called Pan tiles
• They are Moulded by potter – hand
moulded and hence Not very dense or
strong They offen have high absorption values
and hence Can suffer greater wear and tear
The pan tiles differ from pot tiles in that
way they are first made as tiles and the
Curvature is given while the clay is in green
stage they are generally used in rural areas
21. Flat Tiles
• Specifications is as per IS: 2690 Part II
– 1975
• They are almost Rectangular, uniform
in size and shape. Shall be Free from
distortions such as bends, twists and
cracks .
• A Minimum compressive strength: 75
kg /cm2 and a Maximum absorption
value: 20%
• They are Used alone or in combination
with pot tiles for roofing in common
buildings.
22. Allahabad Tiles
• They are a Better class of roofing tiles,
generally Made from superior quality of
clays and by machine pressing. The
Essential part of this tile is a flat tile provided
with interlocking arrangements at the sides.
The Flat tiles – tapering dimension with
bigger end 30 cm and smaller end 25 cm
width Length: 40 cm.
• Flat tiles are laid side by side and joints
between the adjacent tiles are covered with
half-round pot tiles which overlap each
other this results in an appealing roofing
pattern
23. Mangalore Tiles
• They form a Very popular class of roofing tiles in
southern and western part of our country.
• They are So named due to early manufacture in
Mangalore, South India. The Important feature is built-in
interlocking arrangement at the sides
• Provides better roofs, simple construction at economical
costs
• Important characters as per IS 654-1972:
• Shape of Nibs: Free from twists, bends, laminations, cracks,
blisters etc.
• At least two nib, each with base width not less than 19 mm and
projecting above the surface not less than 10 mm
• Dimensions and Weight: 410 x 235 mm; 420 x 250 mm; 425 x
260 mm
• Weight of six tiles dried at 105 ⁰ C + 5 ⁰ C not less than 2 kg not
more than 3 kg
• Classification:
Type Moisture absorption Avg. breaking load
Class AA Less than 10% 102 kg /cm2
Class A Less than 24% 68 kg /cm2
24. Corrugated Tiles
• They are Similar to flat tiles in the
making except their surfaces are
contorted during the moulding stage
in this way, these tiles resemble
corrugated galvanized Iron (G I Sheets )
• Size: 40 x 35 cm
• When used over the roof, a side lap of
one or two corrugations is formed
which gives pleasing effects.
• They have an additional advantage
of Quicker drainage of rain water.
25. Clay Drain Tiles
• Those tiles which are manufactured from clay for special purpose
of lining of drain are called drain tiles. In shape they are circular or
semi circular Their size is determined by the exact purpose for which
they have to be used e.g. in irrigation drains or in domestic drains
26. Terra Cotta
• Terra Cotta means burnt clay, It may be defined as a clay product, which is made by very
careful burning. Terra Cotta requires more homogeneous and purer type of clay, High quality
earthenware which is used as a substitute for stone for ornamentation of buildings.
• Terra Cotta products include: hollow blocks, ornamental and decorative blocks
• Manufacture: Terra cota is manufactured in the same four stages as applied for brick making
and tile making.
• Stage I – Preparation of clay
• The Clay for terra cotta should contain higher proportion of alumina and iron oxides and less
proportion of sand and lime the clay should be Free form impurities like pebbles, grit, lime and
organic material very often, Ground glass, old terra cotta and refined pottery are added before
crushing.
• The clay and other Materials are then finely crushed and reduced to a fine powder using
grinding mills and water is added and thoroughly mixed. Using spades. It is Left for seasoning for
a few days and thoroughly mixed in Pug Mill, till converted into very homogeneous mixture of desired
plasticity. Since terracotta is made in various Colour the color imparting pigments are added at this
stage for thoroughly dispersed in the mass.
29. Manufacture
• Stage II – Moulding: The moulding is done for terra cota using both Hand
moulding, Machine moulding
• The Moulds for terracotta product is made of – Plaster of Paris, zinc. Wooden
moulds not suitable due to very sticky nature of the mix and the intricate shapes
of terra cotta. Sand is sprinkled inside the mould and lump of finely mixed plastic
clay is pressed into the moulds.
• Any desired designs and patterns are given only at this stage.
• Stage III – Drying: The mould product are dried in two stages
• Initial drying: Takes place in the mould itself. It will come out of mould easily on
slight tamping, as on drying the clay mix will shrink to some extent.
• Final drying: Is done by placing the products in well-protected, airy sheds where
direct sun, rain and stormy winds not disturb the products.
31. Manufacture
• Stage IV – Burning: Terra cota products are made by burning the above moulded units
in special furnaces called Muffle furnace in such a furnace there is perfect control over
temperature .
• The Dried products are kept in rows, one above another in muffle furnace and burnt to
temperatures as high as 1200⁰ C . The Temperature is raised gradually but burning is
continued for about four days.
• Burning is discontinued and the terra cotta products allowed to cool in the furnace itself
for four to five days.
• A batch requires about ten days for burning and cooling.
• Uses: All kind of ornamental work, used as building material in form of shaped blocks
• Advantages: Can be easily cleaned
• Light in weight
• Strong & durable
• Can be moulded into desired shapes, available in several colours
• Fire-proof, not affected by acids and atmospheric agencies
• Cheaper than finely dressed stones
33. Earthenware
• They are Made from refined type of clay mixed with other suitable materials. Such
mixtures are Burnt carefully and also cooled very slowly They are Porous in textures
and soft in character They are also made hard and impervious by glazing their
surfaces
• Common use – cable conducts
• Terra cotta, porcelain – types of earthenware
• Porcelain: It is also a very fine type of earthware it burns white, depending upon
composition made translucent, semi-transparent wares. The required material are:
• Materials – clay of high plasticity, feldspar and quartz (SiO2)
• Materials are finely crushed to powder form and little water is added to make a stiff
paste
• Articles – tea-sets, dinner-sets, sanitary wares, electrical insulation
• They burnt at vey high temperatures above 1300⁰ C in muffle furnace and cooling is
done in a very controlled manner.
36. Stoneware
• Stonewares are actually clay products that have been made perfectly
opaque, & Impervious by suitable adjustment.
• They are Made from refractory clays, crushed pottery, feldspars,
powdered stone
• The above ingredients are Mixed together, crushed into a fine powder,
moulded in desired shapes by using pattern moulding.
• Burnt at very high temperatures
• Properties: Impervious, opaque, dense, can be easily clean, highly
resistant to the action of acids and other corrosive chemicals
• More compact and dense than earthenware
• Use: Drain & sewer pipes, sanitary wares and for storage of chemicals
and food products
38. Glazing
• Definition: It may be defined as Protective treatment given to a certain
class of clay products with a view of improving their appearance and to
protect them against weather, sewage and chemicals
• A glaze is the thin film or glassy coat having 0.1 to 0.2 mm thickness on
the surface of the clay products as a result of glazing.
• Objectives:
i. To improve its resistance to water, chemicals and atmospheric gases
ii. To improve its durability
iii. To impart a pleasing finish and decorative design on its surface
• Glazing Processes:
i. Salt Glazing
ii. Opaque Glazing
iii. Porcelain Enamelling
40. Salt Glazing
• This Process is employed to impart a transparent lustrous finish to
products of stoneware categories. It consist of Throwing a sufficient
quantity of common salt (NaCl) in the kiln where the products are being
burnt at high temperatures of 1200 ⁰ C
• At this high temperature, thrown salt gets vaporised and the
vapours spread over the entire surface of the articles It forms a thin
layer of sodium silicate or glaze on chemically reacting with the hot
surface of the article.
• Salt glazing is not practicable for inferior type of clay products.
• Useful for sanitary pipes and chemical stonewares.
42. Opaque Glazing
• Opaque Glazing: This is a very common process of making the
surface of some domestic and general appliances of metallic nature
very smooth and resistant to chemical and deterioration by dusting
they are widely for domestic applications like crockery and sanitary
wares.
• Materials – fine quality clay, feldspar, flint, boric oxide and metallic
oxide like tin, zinc and lead
• Process consists of preparing a very fine, homogenous lean paste of
glazing compounds and dried thoroughly.
• Put into kiln for burning at high temperatures and during this
process coating or glaze compositions get completely vitrified. They
form a uniform glaze of desired colour over the surface of clay ware
which also gets baked simultaneously.
44. Porcelain Enamelling
• Porcelain Enamelling: Making the surface of domestic and general
appliances of very smooth, resistant to chemicals and deterioration by
dusting
• The best variety of clay (kaolin or china clay) is used and crushed
into finest powder, mixed with calculated quantity of water to
make a thin paste.
• The article to be enamelled is given a uniform coating of this slip
using a spray gun and then subjected to heating in furnace at very high
temperature around 1500 ⁰ C.
• The glaze material gets uniformly dispersed and stuck to the metal
surface very firmly.
