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CLAY and CERAMIC PRODUCTS
Prof. Vineet Kothari
Civil Engineering Department
Nirma University
Clay Tiles
• Tiles-thin slabs of burned clay or ceramics used to cover roofs and floors.
• Several tiles: Terrazzo tiles made of concrete, rubber tiles made of rubber,
and even glass, stone, and metal tiles.
• Clay tiles are expensive and labour intensive-have pleasing appearance, long
life, and good properties.
• Based on application called roofing tiles, flooring tiles, wall tiles, glazed tiles
for roof and walls, and vitrified tiles.
• Bricks and tiles are generally manufactured together (See Chapter 3).
• Before firing at 900-1200oC, tiles are treated with engobe or slip (i.e., slurry
of finely ground clay coloured with oxides, carbonates, and stains).
• Engobe is applied by dipping, pouring over or spraying on unfired clay tile.
• Engobed clay tiles can have matt, matt-glossy, or glossy surfaces.
• Though hand-made until the 19th Century, now made using tile-making
machines.
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CLAY ROOFING TILES
• Durable, natural, and sustainable & improve with age and
weathering.
• Require little maintenance and are designed to protect the interior
of the building from rain. Roofing tiles can be of clay or concrete.
• Transportation cost is minimal, as locally available materials are
used.
• They offer high levels of insulation and are fire-resistant.
• Choice between clay and concrete is made based on functional,
aesthetic, and durability considerations.
• Hung from battens by fixing them with nails. (Battens run
horizontally along the length of the roof).
• Tiles run in parallel rows, with each row overlapping the row below
to prevent rainwater from entering.
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Flat Plain Tiles
• Rectangular flat tile measuring 150 to 250 mm × 75 to
200 mm [IS 2690].
• Made in the same way as floor tiles but are not glazed.
• Machine-pressed/machine extruded or hand-made
burnt clay flat terracing tiles are used for flat roof
finishing over lime concrete or cement concrete base.
• Depending on the degree of protection necessary,
they are used in two or more courses.
• Hand moulded tiles are identified by letter H and
machine moulded tiles with M, marked on them.
• A minimum of 25 degree slope is necessary for any
tiled roof.
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Characteristics of burnt clay
Flat terracing tiles
•Batten or Purlins are 25 mm thick and 50 mm wide wood strips nailed to the
roof or rafters, upon which the tiles are attached.
•Interlocking plain tiles are now available, which will result in reduced labour
costs, use of less material and energy, and require fewer tiles per m². These
tiles reduce roof costs by around 40%.
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Roofing with Plain tiles
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Mangalore Pattern Roofing Tiles
• It is an interlocking roof tile with a particular pattern.
• Has two batten lugs at bottom to lock-in with the purlin-there
are also two eaves lugs.
• Are laid over wooden purlin/steel frameworks. Lugs project by 7-
12 mm. No need to nail tiles down, reducing labour costs.
• The average weight of 6 tiles (dried at 105 to 110°C) is 2-3 kg.
• Tile-to-tile linking of double groove tiles (cost 40% more) is better
than single groove tiles. Interlocking reduces chances of leakage.
• Single groove tile is used as decorative tile over RCC sloped
roofs.
• In cyclonic zones, minimum one hole is provided in one of the
cross ribs to secure it to the batten with a wire, so that they are
not lifted off during high winds.
Classification and Dimensions of
Mangalore Pattern Roofing Tiles
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Sample size and criterion for
conformability, as per IS 654
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Single and double grooved Mangalore
tiles
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Mangalore Roof Tiles - Over RCC
Sloped Roof
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Clay Half-Round Country Tiles
(Spanish Tiles)
•Half round country tiles
are commonly used in
villages (called as Spanish
tiles).
•They are laid in pairs as
under-tiles and over-tiles.
•The under tiles are usually
laid with their narrow end
towards the eves, whereas
the over-tiles are laid with
their wide end towards the
eves.
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Allahabad Tiles (Italian tiles)
•Consists of two types of
tiles–over-tile and under-
tiles.
•Bottom tiles are flat, with
tapering upturned flanges at
the sides.
•The over-tiles are half-round
and tapered.
• The trough tiles are 235 ×
395 mm in size and the top
tiles are 165 × 395 mm in
size.
The under-tiles are laid side-by-side and the •Both these tiles are tapering
joints are covered by the half-round tiles. towards one end. The taper
Over-tiles are fixed to vertical battens with 75- in the over-tile allow the tile
mm nails. in next course to fit in.
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Solar Roof Tiles
Similar in design to conventional
roof tiles but have photovoltaic cell
within to generate renewable
electricity.
• Tesla and SolarCity developed a solar roof system using a high-
efficiency solar cell (Panasonic) and covered with a ‘colour louver film’,
which allows cells to blend into the roof while exposing them to the
sun above, and finally a tempered glass on top for durability.
• Are more than three times stronger than standard roofing tiles.
• Tesla is offering tiles in four different styles – textured glass tile, slate
glass tile, tuscan glass tile, and smooth glass tile.
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CLAY FLOORING TILES
• Made from good soils of even texture and are well burnt, to
enable thin tiles having smooth surface.
• To make them hard and impervious, a mixture of ground
glass and pottery ware may be added.
• They are extruded, pressed, and fired at ~1300°C. They may
be salt glazed for better appearance.
• Their faces may be plain, grooved, fluted, etc., and edges
made square.
• The depth of the grooves on the underside of flooring tiles
should not exceed 3 mm.
• The warpage < 2% along the edges and <1.5% along the
diagonals.
• Half rectangular and triangular tiles are also available.
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Classification of flooring tiles
as per IS 1478:1992
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Dimensions of sides, thickness, and
tolerance of flooring tiles
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Clay Vs Concrete Roof Tiles
• Manufacture: Clay tiles are manufactured from locally available earth and
hence are environment friendly, and easily recycled. Whereas concrete is
made from Portland cement, aggregates, and water.
• Durability: Both are durable and strong. But the lifespan of clay is longer
(50 years). Clay tiles also resist wind, rain, or moisture effectively.
• Colour: Colour of clay tiles is red or terracotta colours. Glazing may be
used to change the colours. These colours do not fade with time. Although
concrete can be finished with any desired colour it tends to fade with
time.
• Cold weather: In cold weather, clay tiles may crack or shatter due to
freezing and thawing. Hence, preferable in warm climates. Concrete can
be used in any climate.
• Weight: Clay is a bit heavier than concrete. Hence, should be used only
after checking the load carrying capacity of supporting members.
• Cost: Concrete tiles cost less but life cycle cost of clay tiles may be less, as
they have longer lifespan.
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Ceramic Products
• Many different types of engineered ceramic products.
• Are based on nitrides (silicon and aluminium nitride), carbides(silicon and
boron carbide), and oxides (alumina and zirconia).
• Processing involves high temperature, and the resulting materials are heat
resistant or refractory.
• Based on their constituents and glaze, these products exhibit resistance to
corrosion and chemical substances, wear, and water.
• As they are made from high-purity raw materials their properties will be
consistent.
• They are composed of diverse materials, which make them suitable for varied
applications including construction.
• Facing bricks, roofing, flooring, wall tiles, and sewer pipes, are used in the
construction industry.
• Ceramics ensure longer life and low maintenance
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Manufacturing of Ceramic Products
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Steps in Manufacturing of Ceramics
• Raw material procurement:
– Raw materials range from impure clay materials from mining to ultrahigh
purity powders prepared by chemical synthesis.
– These raw materials, after extraction, are transported and stored at the
manufacturing facility.
• Beneficiation: This is done in the following steps.
– Comminution is the reduction of size of raw material to ~ 1.0 µm using
Ball mills.
– Purification is done by filtering and acid leaching (to remove metal
contaminants).
– In sizing and classification, different size of materials are separated.
– In calcining the material is heated (below its melting point) to liberate
undesirable gases.
– The dry powders are granulated to improve flow, handling, packing, and
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Steps in Manufacturing of Ceramics
(contd..)
• Mixing:
– Pug mills often are used for mixing ceramic materials.
– Binders are added during mixing to impart strength.
– Plasticizers to increase the flexibility of the ceramic mix.
– Lubricants to lower frictional forces between particles. Water in slurry
processing; deflocculants and surfactants may also be used .
• Dry Forming:
– In dry pressing, ceramic powder (moisture content of 5–15%), is
compacted between plungers in a die cavity.
– In isostatic compaction, ceramic powder(0–15% moisture) is placed in
flexible mould, de-aired, sealed & pressed in pressurized chamber.
– Vibratory compaction- irregular shapes from ungranulated powders.
– Extrusion, jiggering, and powder injection moulding used in plastic
moulding.
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Steps in Manufacturing of Ceramics
(contd..)
• Green machining:
– After forming, the shapes may be modified slightly, or the
rough surfaces and seams are eliminated by machining.
• Drying by convection:
– Heated air is circulated around the ceramics using tunnel
kilns .
– An alternative to air drying is radiation drying in which
microwave or infrared radiation is used to enhance drying.
• Presinter thermal processing:
– Prior to firing, ceramics are often heat-treated (bisque
firing) at about 700 to 1000°C, for additional drying,
vaporize or decompose impurities, and remove residual,
crystalline, and chemically bound water.
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Steps in Manufacturing of Ceramics
(contd..)
• Glazing:
– The surface of bisque-fired ceramic-ware is glazed (by spraying or
dipping) prior to firing. These glazes provide a smooth and shiny surface,
sealing the pores.
– Glazes classified as raw glazes or frit glazes. A frit glaze is a pre-reacted
glass and the raw glazes are quartz, feldspars, carbonates, borates, etc.
– Copper oxide gives a green colour and iron oxide gives a red colour.
• Firing and cooling:
– Fired at 50–75% of melting temperature (900–1300°C), and then cooled
to 20 C.
– Can also fired by applying pressure, which decreases firing time.
– Electric resistance-heated furnaces are used to fire advanced ceramics.
Further processing such as abrasive grinding, chemical polishing etc.
• Packaging:
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Properties of Ceramics
• Ceramics are brittle, hard and strong in
compression, weak in shearing and tension.
• They posses excellent wear resistance, good
frictional behaviour, low thermal conductivity.
• Have corrosion resistance in acids and alkalis, and
excellent surface finish (Ra = 0.006 µm).
• Have modulus of elasticity similar to steel, and
thermal expansion coefficient similar to cast iron.
• They are anti-static, and non-magnetic.
• See also IS 2840
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Classification of Ceramic Tiles
• According to method of manufacture, classified
as:
• Extruded tiles (shaping A) - Tiles whose body is
shaped in the plastic state using extruder.
• Pressed tiles (Shaping B) - These tiles are formed
from small grains and shaped in moulds at high
pressure; they may be glazed or unglazed.
• Cast tiles (Shaping C) - The body is cast into a
mould or on to a porous refractory batt that
absorbs water.
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Classification of Ceramic Tiles
According to the water absorption (percent by mass) classified as (IS 15622):
1. Tiles of very low and low water absorption (Group I)
(a) E < 0.08% [Group BI(a) ]- Ceramic fully vitrified tiles
(b) 0.08% < E 10% (Group BIII) - Ceramic wall tiles
2. Tiles of medium water absorption (Group II)
3%< E 10% (Group BIII) - Ceramic wall tiles
3. Tiles of high water absorption (Group III)
E >10% (Group BIII) - Ceramic wall tiles
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Ceramic Tiles
• Ceramic tiles are less expensive than natural stone.
• It is possible to mix and match tiles of different colours,
patterns, and sizes to create custom designs.
• Glazed ceramic tiles such as Spartek tiles, made from special
clay and coloured glazing, were used only for walls. Improved
techniques have made them possible to be used even in high
traffic areas like airports.
• Modular tiles ranging in size from M100 × 100 mm to M300
×300 mm, and non-modular tiles ranging from 100 × 200 mm
to 400 × 400 mm (IS 15622).
• Dry pressed tiles: thickness 3 to 11 mm, whereas extruded
products are thicker: 10–20 mm and more.
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Ceramic Floor Tiles
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