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In the Near East and India, bricks have been in use for more than five thousand years. The Tigris-Euphrates plain lacks rocks and trees. Sumerian structures were thus built of plano-convex mudbricks, not fixed with mortar or with cement. As plano-convex bricks (being rounded) are somewhat unstable in behaviour, Sumerian bricklayers would lay a row of bricks perpendicular to the rest every few rows. They would fill the gaps with bitumen, straw, marsh reeds, and weeds.
The Ancient Egyptians and the Indus Valley Civilization also used mudbrick extensively, as can be seen in the ruins of Buhen, Mohenjo-daro and Harappa, for example. In the Indus Valley Civilization particularly, all bricks corresponded to sizes in a perfect ratioof 4:2:1, and made use of the decimal system. The ratio for brick dimensions 4:2:1 is even today considered optimal for effective bonding.
The Romans made use of fired bricks, and the Roman legions, which operated mobile kilns, introduced bricks to many parts of the empire. Roman bricks are often stamped with the mark of the legion that supervised its production. The use of bricks in Southern and Western Germany, for example, can be traced back to traditions already described by the Roman architect Vitruvius.
In the 12th century, bricks from Northern Italy were re-introduced to Northern Germany, where an independent tradition evolved. It culminated in the so-called brick Gothic, a reduced style of Gothic architecture that flourished in Northern Europe, especially in the regions around the Baltic Sea which are without natural rock resources. Brick Gothic buildings, which are built almost exclusively of bricks, are to be found in Denmark, Germany, Poland and Russia. However, bricks were long considered an inferior substitute for natural rock.
During the Renaissance and the Baroque, visible brick walls were unpopular and the Brickwork was often covered with plaster. It was only during the mid-18th century that visible brick walls regained some degree of popularity, as illustrated by the Dutch Quarter of Potsdam, for example.
The transport in bulk of building materials such as bricks over long distances was rare before the age of canals, railways, good roads and large, reliable heavy goods vehicles. Before this time bricks were generally made as close as possible to their point of intended use (it has been estimated that in England in the eighteenth century carrying bricks by horse and cart for ten miles over the poor roads then existing could more than double their price).
The use of brick in construction was not limited solely to regions that lacked stone or other materials suitable for building close at hand, bricks were often used, even in areas where stone was available, for reasons including speed of construction and economy. During the building boom of the nineteenth century in the eastern seaboard cities of Boston and New York, for example, locally made bricks were often used in construction in preference to the brownstones of New Jersey and Connecticut for precisely these reasons. However, bricks were also used in regions that lacked stone and other materials suitable for building, including, for example, much of south-eastern England and The Netherlands, places lacking easily-worked stone but having access to clays suitable for brick making and fuel for firing.
1.1Clay extraction
The clay pit is usually nearby the producing plant. This reduces the distance for transportation to a minimum. The clay is extracted from the clay pit by modern equipment, stored and transported to the clay preparation unit.
1.2 Clay preparation
At the clay preparation the clay is going to be grinded, milled, wedded and foreign materials such as stones are being removed to get the right consistency and homogeneity of the clay for production. For special colours different types of clay or mineral aggregates can be added.
1.3 Shaping process
For many thousand years bricks have been shaped according to the soft-mud molding method. The bricks have been shaped by throwing with both hands a clot of prepared clay into wooden frames and where the surplus clay got cut off by using a metal wire or a piece of wood. Today bricks are still produced following the same main principles. But nowadays modern machines have taken over the brick maker’s job. Bricks produced by this method are called
Hand molded brick: for the mechanical produced “hand” molded bricks, the raw material is, depending on the machine producing these bricks, either rolled in sand or directly being thrown forcefully into already sanded moulds. The sand acts like flour in a cake mould. The surplus material is being cut off from the top edge of the moulds.
or
Stock bricks: The raw material is being pressed into the already sanded moulds under high pressure. This results in bricks with more subdued shapes and surface structures, and like hand-moulded bricks, five surfaces of the brick are sand-coated.
Extruded bricks are being produced by extrusion. Under high pressure, the raw material is being forced through a die. The produced endless run of clay is being cut into the thickness of the green brick by a taut wire.
1.4 Drying and Firing
By using the excess heat energy of the kiln the green bricks are dried until nearly all moisture has been removed. Now the unfired brick is prepared for the following firing process in the kiln.
At a temperature of about 1050 îC, for pavers over 1100 îC, bricks are fired in the kiln. Today the firing process usually takes place in modern, computer controlled tunnel kilns. But there are still some traditional ring kilns and clamps at work, to produce bricks with a very special look. By using special firing methods, like using a reducing kiln atmosphere, it is possible to produce exceptional colours.
1.5 Packaging
After the fired bricks have cooled down, they pass a quality inspection. Then they are packed onto pallets and rapped with a pallet foil to save the bricks from water and dirt. They are now ready to get delivered on stock or the building sight.
2.1 Raw materials management
The first phase involves the extraction of clay, the main raw material for bricks, in an environmentally compatible process and transportation to a nearby plant for processing.Wienerberger is dedicated to restore former clay mining sites.
Clay pits that are no longer used are returned to serve as a habitat for flora and fauna or create a natural recreation area for local residents, or are restored for use by agriculture or forestry businesses.
2.2 Preparation of Clay
The clay is prepared and made workable in a second step by grinding, mixing, wetting and cleaning to remove foreign materials such as stones. Additives (e.g. sawdust) are then added before further production. Technical progress now makes it possible for us to use lower quality clay that was formerly disregarded as residue.
2.3 Shaping
This step involves the actual shaping of the roof tile, where either the prepared clay
is pressed through dies by extruders or pressed into forms and made into pressed tiles. Our in-house die and form manufacturing allows us to develop our own special tile forms and die forms, which represent the basis for innovative products with new shapes as well as optimized product features.
2.4 Drying
The drying process prepares the brick for firing by removing the moisture from the soft "green" brick. New and more efficient drying and air stream technologies have reduced the drying period to one-third of the originally required time. This lowers energy requirements, improves product quality and helps us develop new products.
2.5 Colouring
After the drying process the clay roof tile, except it remains natural red, is either engobed or glazed.
Engobed clay roofing tiles have matt, matt-glossy or glossy surfaces. Engobes are applied as clay-containing slips by dipping, pouring over, centrifugal casting or spraying on the still unfired clay tile.
Glazed tiles are covered with a very hard continuous glass layer that closed all pores and makes the tile extremely water-resistant. at the same time this glass layer gives the tile its special shiny look.
2.6 Firing
For Clay roof tiles that are produced with a ceramic surface (engobe or glaze), this is burned in during firing process.
The firing of the tiles at a temperature of 900 to 1200°C in a tunnel kiln is the final part of the production process. After this step, the finished product is available for use. After firing, brick products are nonflammable and fire-safe for ever. Kiln and firing technologies as well as air stream systems have reduced the required firing time by up to two-thirds. This has created enormous advantages: a 50% decrease in the use of primary energy over the past ten years, up to 90% less emissions through thermal post-combustion equipment, optimized product quality and a substantial increase in capacity.
2.7 Packaging
The fired tiles are loaded onto palettes with automatic equipment, and normally enclosed with pallet foils.
2.8 Delivery
Wienerberger has a network of decentralized production facilities. The plants are located near to raw material supplies and as close as possible to local markets. This reduces transport distances, which makes fast delivery possible and also lowers the environmental impact.
3.1 Disassembly of Clay
As a first step, the assessment of the quality of raw material is done by experienced geologists. After that the excavated clay is laid in layers on stockpile and is kept outside for about one year to ensure consistency.
3.2 Processing of Clay
At the second stage clay is collected from the stockpile and shoveled into the box feeder. Water, sand and saw dust are added to the clay in the mixer and are mixed to the correct consistency. Following, the clay is fed into the grinder where it is reduced in size to small granules. A conveyor transport the ground clay to the clay stock. And finally the mixed clay is dropped into the extruder.
3.3 Extrusion
During this step the brick mass is pushed through a die and then cut into individual bricks. One die is sufficient for up to 10mn. brick units. The 'green' (wet bricks) are put on pallets and automatically transferred to the dryer.
3.4 Drying
Drying takes up to 36 hours for thinner bricks and up to 45 hours for thicker. Moisture content of a brick drops from 20% to 2%. After the process of drying the bricks are automatically repackaged into a firing setting and automatically transferred to the kiln by kiln cars.
3.5 Firing
After drying the bricks are then fired for 6-36 hours in the kiln, which is usually heated by natural gas or coal at a temperature >900°C. Through firing, clay gets strength, while burnt pulp and saw dust create small holes inside bricks, which increase the heat insulation.
3.6 Grinding
Optionally, to produce high margin plain bricks, the bricks are passed through a grinder for reduced construction time.
3.7 Packaging
After removal from kiln cars and grinding, the bricks are packed and made ready for shipping.
3.8 Delivery
Packaging bricks are taken outside the plant by forklifts and placed for storage.