Roof tiles
Roof tiles are flat, coarse ceramic components made of fired clay that are used to cover pitched roofs . This is then tile roof called and is part of the roof drainage . A coherent row of roof tiles is called a bundle .
The tile roofing can consist of traditional, unfolded roof tiles such as hollow tiles , or monk and nun tiles or of modern folded tiles such as double groove tiles , reformed or flat roof tiles . The quality of the brick model in terms of rainproofness and the type of second drainage level determine the roof pitch.
In addition to roof tiles, there are other natural roofing materials, e.g. B. finely split slates with which the slate cover is made.
In addition to the natural ones, there are also artificial roofing materials such as concrete roof tiles or elements made of copper or zinc for the manufacture of metal roofs.
Differentiation from Dachstein and other roofing materials
Roof tiles and roof tiles differ mainly in material and manufacture. While a roof tile is made from natural minerals, usually clayey masses, usually without additives, roof tiles are made from concrete.
In modern roof tile production, irregularities such as color deviations or deformations are counteracted. The difference in manufacturing also affects the color scheme. The color of a roof tile can vary slightly. This is due to the natural raw material. The color results from the raw material and the firing technique used. Engobes and glazes also consist of minerals, are burned in and are therefore UV-resistant and durable.
In the case of a roof tile , the color is added and can therefore be regulated.
Depending on the region covering the inclined roofs was originally with locally occurring materials such as grasses , straw , reeds ( reed ), wood or slate . These natural building materials were replaced in the course of building history in southern and northern Europe by the architecture used by the Romans, which was particularly focused on the processing of trass mortar and clay bricks .
History of the roof tile
It is not known when exactly and by whom the clay roof tiles were invented. However, there is a report by the Greek writer Pindar , in which he discovered the invention of the roof tile in 450 BC. Attributes to the Corinthians. While there is only sparse information on the history of the roof tile, apart from original pieces (e.g. from archaeological finds), the history of the wall tile is recorded in numerous writings by ancient scribes and proven by excavations. For the history of brick production and masonry bricks, see the article Brick . Today's manufacturers of roof tiles have hardly any documented evidence or photos from the early days - meaning the period of the last 150 years - of industrialized roof tile production. The reasons for this lie in the early days of industrialization when there were many small production facilities. Many farmers operated the roof tile production as an additional source of income and to bridge the winter time.
The establishment of the roof tile as a building covering took place in today's area of Lower Saxony, which can be transferred to other areas in today's Germany, in five phases. During the Middle Ages , in the 9th and 10th centuries, strip bricks based on the Roman model were used, which were only used in special buildings, such as sacred buildings. In the 11th century, pre-forms of roof tiles of the monk and nun type appeared and there were flat tiles. In the 11th and 12th centuries, hard roof coverings became more common, which were no longer limited to the sacred area, but also extended to the castles and aristocratic residences of secular lords. In the 13th century, roof tiles became more common, especially in the cities, but remained limited to the social upper class. In the 14th and 15th centuries, cities took on the pioneering role in the expansion of the roof tile, and there were new types such as the S-pan and the skirted tile. From this phase onwards, cities promoted hard roof coverings and thus ensured mass distribution.
In the period of handmade bricks, there was a special feature, the so-called Feierabendziegel (also known as chance or sun brick). They were the last bricks of a day's work, into which ornaments, dates, symbols and even texts were carved on the back with the finger, a comb or other pointed object. The oldest known after-work bricks come from the time between 1100 and 1300 AD.These must be distinguished from accidental impressions on Roman bricks: They were laid out on the floor to dry before the fire and animals or children often ran over them so that they could walk - or paw prints were made.
The onset of industrialization also changed the production of bricks: the invention of the steam engine made it possible to manufacture roof tiles industrially on a large scale. One can Wilhelm Ludowici ( Ludowici Ziegelwerke ) as inventors (1881 application of his patent for interlocking tiles Z1) denote the machine-made roof tile. The first industrially manufactured roof tiles were delivered on horse-drawn carts and packed in straw.
The ovens ran on heavy fuel oil until the 1960s and then gradually switched to natural gas. Since that time, there have been problems with the frost resistance of the roof tiles in many plants, which then led to a mass death of the old roof tile industry and a boom in the concrete industry and its cheaper-to-manufacture pans. Only a few plants survived this phase. Some of the oldest production facilities are on the Lower Rhine on the Dutch border. The place Tegelen near Kaldenkirchen, located directly behind the Dutch border, already reveals the old tradition from Roman times by its name. The name Tegelen can be traced back to the Latin tegula , brick .
Composition of the roof tiles
Freshly pressed clay bricks consist of about 60% by volume of solid components ( clays and loam ) and about 40% by volume of water-filled pores that have to slowly dry out before firing.
Clays and loams are natural components of the earth's crust and, as the weathering products of rocks, consist largely of clay minerals and quartz . Feldspars and iron minerals also make up a small proportion of the mass. The color of the clay roof tile is created by the respective firing temperature and the iron oxide content in the raw material.
Manufacturing
Handcrafted
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In the settlement areas of Europe conquered by the Romans, roof tiles ( Tegulae and Imbrices ) were found on the roofs of the Roman fortifications , in cities, village-like settlements ( Vici ) and in villas in the countryside. In the Middle Ages , church roofs and other public buildings (castles, palaces) were initially covered with tiles. Initially, only high dignitaries were able to afford financially in the settlements to cover their roofs with clay roof tiles. For example, at the Synod of Frankfurt in 794 , Charlemagne wrote clay roof tiles as general roofing for his farmhouses. At the beginning of the 11th century, Bishop Bernward von Hildesheim set up a brick kiln to have flat and hollow bricks burned for his buildings. He took over the name stamping of the bricks from the Roman legions.
From around the 12th century, the economic exploitation of brick production began, with which it was possible to burn in reserve. The production was still very laborious and tedious: the clay was dug under layers of humus , swamped in pits or piled up in hills and allowed to freeze through for a winter. In some areas the clay was even stored for two winters, only to be heated, pounded, crushed and kneaded with water. This semi-plastic clay cake was pressed by hand into a wooden mold and then rubbed off with a board. The resulting blank then dried in the air in the shade for at least one summer. After that, it was stacked in field furnaces and gradually burned at a high temperature. After the fire, the material was slowly cooled - so there was only a relatively limited number of roof tiles available. This workflow described dragged on over a period of more than one and a half years. Large buildings therefore had to be burned to ensure that there was enough stock before construction could begin. In addition, a large number of craftsmen and assistants were necessary.
Only rich builders could afford such an elaborately manufactured building material. Brick buildings were either built on a princely order or were commissioned by monasteries and bishops . In the later heyday of the Hanseatic League , rich bourgeois merchant families often built their houses splendidly out of bricks and covered them with colored glazed roof tiles ( brick Gothic ).
As early as the 12th century, people knew not only the advantages but also the limits of the roof tiles. For example, around 1165 the Ministeriale Cuno von Würzburg covered its Wetterau Castle with different roof tile shapes. The representative area received a covering of beaver tails , the farm buildings is covered with coarse elutriated hollow bricks and the conical roof of the keep with slate cover. In the settlements of the "normal" people, straw, reed and wood shingle roofs predominated. Only in the course of the 14./15. In the 19th century, tiled roofs were more common in the narrow towns to protect against fire. In 1342, Emperor Ludwig, the city lord of Munich, agreed with the city council that new buildings should only be covered with fired clay roof tiles. The citizens of Bern in Switzerland were even reimbursed half of the construction costs from the city treasury by a council resolution of 1405.
Modern manufacturing
In principle, brick production has not changed significantly. While brickworks used to be built near brick pits for cost reasons, the problem of transport plays a subordinate role today. The shaping has essentially been automated. The individual manufacturing steps are:
- Dismantling
- processing
- Swamps or Mauken
- Shaping
- dry
- Burn
- Quality check
When swamping or mucking, the moisture content of the clay / loam mixture is adjusted to the desired value. The mined clays and loams have different moisture contents when they are mined, which must be balanced. The drying process is also important. The blank must be dry, because water increases its volume by 1500 times when it evaporates. The smallest amount of water trapped in the raw material would destroy the broken glass in the event of a fire.
Coloring
Roof tiles are produced in different colors and surfaces. One differentiates:
- Natural red roof tiles
- Muted roof tiles (colored through)
- Engobed roof tiles
- Glazed roof tiles
Natural red roof tiles get their color from the iron oxide contained in the clay . Natural red is not a coating; therefore the roof tile is natural red through and through. Natural red means iridescent.
Muted roof tiles are colored in the layer close to the surface or - just like natural red roof tiles - completely colored. The formation of iron oxide is suppressed by removing oxygen during the second fire process; the color of the brick remains similar to the raw material extracted. By adding certain dampening agents, bluish, silvery or anthracite-colored gray tones are also possible, often iridescent.
There are engobed roof tiles in the earth-colored range. Red, brown, umbra-colored (old-colored), gray and black surfaces are common. Engobes are clay sludges, which by mineral additives, z. B. iron oxide or manganese, burn out colored. Unlike the application of paint, e.g. B. for fiber cement panels or concrete blocks, the engobe is applied to the visible surface of the blank and burned in before firing. This technique creates an intimate capillary bond. Engobes are UV-resistant and absolutely permanent.
Glazed roof tiles are given a transparent or colored coating of molten glass. The surface is glass-hard, smooth and usually shiny. It tends to pollute less quickly. A self-cleaning activity is not achieved by glazed surfaces. Almost all colors are possible. There are transparent, black, red, green, blue, brown, even yellow and purple glazes. Glazes are also UV-resistant, permanent and largely insensitive to mechanical influences. Crackles are unavoidable due to the different materials. Glazed roof tiles have a long tradition. A new trend is the production of such glazed roof tiles without shine and reflection. Such surfaces are called satin finish.
The combination of engobe and glaze represents the noble engobe. If glass bodies are added to the engobe, a so-called noble engobe is created. The surface is then harder and combines the structural characteristics of the diffusible and craquelure-free engobe with the degree of gloss of a glaze. But here, too, the trend towards matt precious engobes is evident.
All of these surfaces have optically architectural motives. This does not have a positive effect on the service life of the roofing ceramic.
Classification of the roof tiles
Roof tiles are small-format roofing elements made of fired clay for hard, rain-proof pitched roofing. Today i come d. Usually industrially produced roof tiles according to DIN EN 1304 are used, which can also be used with flat roof slopes (from 10 °).
A distinction is made between extruded roof tiles and pressed roof tiles.
Strand roof tiles
- Beaver tail
- Hollow socket
- Interlocking tile
Strand roof tiles are produced in an endless strand of clay and cut to size with a wire cutter in the desired length. Since these tiles do not normally have a fold and thus cannot interlock when roofing, they are particularly suitable for roofs with a slope of more than 30 degrees. This means that the rain can drain away more quickly and there is no need for greater protection against precipitation. The manufacturing process was developed by Jacob Schmidheiny in 1880 in the brickworks in Heerbrugg .
Pressed roof tiles
- Double groove interlocking tile
- Reform brick
- Smooth brick and special shapes
- Romanesque bricks
- Flat roof tiles
- Monk and nun , see photo. The concave roof tiles are called nun, the tiles on top of them are called monk.
For the production of pressed roof tiles, the brick material goes into the extrusion press and is then cut into even blocks. In the slide press or the turret press, the blanks are brought into their final shape with the upper and lower molds. Pressed roof tiles are i. d. Usually folded all around and thus offer particularly high-quality protection against rain. For economic reasons, too, large-format roof tiles are more and more popular today. The traditional formats with 15 roof tiles per square meter are becoming less and less important. Medium and large formats with 12 or 10 roof tiles per square meter are trendy. Larger formats up to just 5 roof tiles per square meter are also available.
Shaped brick
Shaped bricks are coarse ceramic bricks with a special shape that complement the surface tiles and form the all-ceramic roof. For the roof tile models described, there are shaped tiles for roof edges; z. B. verge tiles as well as ridge and hip tiles, as well as through tiles, ventilating tiles and a number of other shaped tiles, which offer detailed and visually correct solutions for all today's needs.
The Tegula ledge brick is the oldest brick used in Greece and the Roman Empire. Its butt joints are covered by imbrices (hollow bricks) (Romanesque bricks). This type of cover was also common in the northern provinces in Roman times. Later, however, it was considered unfavorable for the harsh climate north of the Alps . Writes Palladio in his "Four Books on Architecture" in 1570: "In Germania to do because of the large amounts of snow that falls there, the roofs very steep and covered them with small wooden panels, shingles or thin tiles."
In order to better defy the weather, in the Middle Ages the flat sloping slat tile roofs of the Romans north of the Alps were replaced by hollow brick or flat brick roofing. In today's southern Germany, the flat brick, with colored glaze in the late Middle Ages, prevailed in many shapes and designs until the late 19th century. On the other hand, in northern Germany the Krempziegel was preferred , a further development from the hollow brick covering . When the industrial mass production of roof tiles began in the middle of the 19th century, the interlocking tile took over the traditional coverings.
Glazed bricks
In the Deutsche Bauzeitung of 1883, the glazing of the bricks is described:
“Even the Egyptians, Babylonians and Assyrians tried to delay the rapid weathering of the bricks by applying glaze, and at the same time used the protective agent to beautify the goods. The investigations carried out show that glazing was known and practiced even before the invention of brick-burning; and indeed one seems to first have the finished painted and air-dried tiles in the same row that they are supposed to occupy on the roof, laid flat on the ground and painted in this position, respectively. covered with the enamel paints and other glazes, but then to have lit a fire on them. Such glazing preserved the surface, but only it from rapid destruction. Baked glazed bricks were certainly known in the second or new Babylonian empire; the Greeks, Etruscans and Romans also seem to have known them, although no glazed bricks from these three peoples have survived to us. The Lombards used them in the seventh, the Byzantines perhaps even earlier and in the Middle Ages they were used almost everywhere where brick construction was cultivated, even for roofing in house areas. The process of making the glaze seems to have been very different from time immemorial, both in terms of the mixtures for the enamel color, and in terms of the time and manner of application of the same, and is now to the same degree. Some factories color the clay before painting, others wear the enamel color, resp. the mixture, which produces a colored glaze during firing, is applied to the air-dry clay, while others only color after the first firing using such a mixture. - An inquiry initiated by the Association of German Architects and Engineers' Associations from Leipzig on the process, production method, mixing, success, etc. of the glaze has not yet been completed. "
Roofing work
In the "Instructions for Construction Technicians" from 1881 it says:
"The execution of the roofing work is differentiated according to the materials used, and is carried out partly by free workers, partly by a trade."
At this point in time, the later development in the European Union had already been anticipated, because today “other trades” are also working on the roof.
In the chapter "The Tiled Roofs" it says in extracts:
"The roofing with flat tiles ( beaver tails , flatworks, ox tongues, etc.): Flat tiles or flatworks have the shape of an elongated rectangle, rounded or pointed on one short side, with a nose on the other, about 36 to 39 cm long, 15 Up to 15.6 cm wide and 0.6 to 1.2 cm thick. The main requirements of good flat structures are lightness, weather resistance and a perfectly flat, straight shape; Sharp fire, bright sound, areas free of cracks and cracks and poor water absorption are a sign of their quality. In order to achieve a fairly tight and permanent roofing, the stones must lie on their entire surface and must not gape, especially at their lower ends, which is only possible with completely flat bricks and when using evenly thick slats.
The roofing with tiles demands the roof pitch and rafter width of the simple or split roofs; the first, shaped like a lying S, come in three different sizes. The largest format with the nose is on average 42 cm long and 26 cm wide; the middle variety is 39 cm long, 26 cm wide and the length of the smallest, the so-called Dutch pans, is 34 cm by 26 cm wide.
The roofing with brim tiles is done with carefully on the conical up resp. bent edges of matched stones, on battens, with an overlap of 8 to 10 cm. Brick bricks laid in mortar make special spreading unnecessary.
The Wöterkeimer roof stones, an invention of E. von Kobilinsky, are the same in principle and type of cover as the roof tiles and brim tiles; because of their straight shapes, they keep straighter when drying and firing. Laying them in mortar is superfluous, but they have the disadvantage that the water on them collects and drains off in a channel which is directly on the butt joint and promotes its leakage.
The seam tile roofs are named after roof tiles, on the edges of which there are seams that fit into one another in order to provide a tight covering of the roof even without using mortar. As evenness of the bricks as possible and precise interlocking of the seams are essential conditions for fulfilling this task. Among the various forms in which the interlocking tiles have come to be used, interlocking tiles manufactured in Lorraine (Gebrüder Couturier, Forbach) (which are also manufactured by the works in Siegersdorf in Silesia) have proven themselves. In addition, Ludwigshafen, Durlach, Karlsruhe, Hanau and Horrem near Cöln are the most important factory locations for interlocking tiles. "
According to the Deutsche Bauzeitung (year 1876), the following should be emphasized as the main advantages of the interlocking tile covering, "which, when using a weatherproof material, is to be regarded as the ideal of a good tile roof" :
- Lower roof pitch than with a normal tile roof,
- Lower weight,
- Much lower price,
- Quick, easy and convenient execution of the roofing,
- Good runoff of precipitation and therefore faster drying and greater durability than with the tiled roof;
- Exceptionally easy repairs (the broken stone is pushed out and the new one pushed in from the attic);
- “You can simply replace skylights by covering individual stones made of glass at any point. In Forbach, interlocking tiles are manufactured for this purpose, which can be provided with a cemented glass pane. Recently, a construction of interlocking tiles with incisions and pins has been patented, which should enable them to be covered even more easily. "
Laying types
Partly the covering is done with non-rebated roof tiles, partly also the rebated tile covering, using lime cement mortar. A distinction is made between interior lining, crosscut and longitudinal joint .
In the case of internal coating, the transverse joints, and in some cases also the longitudinal joints, are covered with mortar from the inside after the covering has been completed. If the bricks are laid in mortar in the area of the height overlap, this is called a crosscut. In the case of the longitudinal joint, the bricks are provided with mortar on the sides.
Basic rules of the German roofing trade
In the "Instructions for the training of apprentice roofers" from 1926/27 it says about tile roofing:
“The roofing of roofs with tiles is common all over Europe. A distinction is made between two large families of bricks, flat bricks and shaped bricks. The flat tiles include the beaver tails, the shaped tiles include the interlocking tiles, the pans, the brim tiles and the monk nun. In Germany the beaver tails are the most common.
A beaver tail roof is made on battens (or formwork and strips) and can be covered as: a) crown roof, b) double roof or c) simple roof with split ends (shingles), split roof. The roofing is usually from right to left.
An S-pan roof (hollow socket roof) is covered on battens. Pans are covered either with a crosscut and internal coating or dry with internal coating. The pans are covered in lime mortar on the eaves layer, ridge layer and in places where internal lining is impossible. Instead of spreading, cardboard strips, cardboard docks or straw docks (laid under the bricks) can be used.
A monk's roof is covered on slats. The nuns are not placed closer to each other and no further than the width of the monks requires with proper mortar bedding. The nuns are given a cross cut close to their noses, on which the nuns of the next layer are rubbed so that the mortar oozes out inwards. The monks are not completely bedded in lime mortar, but here two narrow longitudinal blows are given, only the head of the monk is filled with mortar before exposure.
A roofing with interlocking tiles is made on battens and, depending on the shape of the tile, as a) ordinary interlocking tile roof (hollow interlocking tile), b) extruded interlocking tile roof, c) monk nun roof (combined) or d) joint pan roof. All seam tile roofs are covered dry, can be spread from the inside or underlaid with strips of cardboard, straw or cardboard docks. To prevent storm damage, interlocking tiles can be secured by wiring, provided they are provided with appropriate eyelets. If such storm protection has been specially agreed, it is considered sufficient if on average at least the third of all stones is tied to the battens. "
Other use
Due to the attractive, natural appearance of the material, the roof tile is also used today as a decorative object, such as a wall candle holder within a harmoniously coordinated interior design.
As a design element and weather protection, roof tiles were also used for facade cladding on battens - especially in the low mountain ranges. This type of application lost its importance through the use of large facades with metal, fiber cement or plastic cladding. In recent years one can observe a certain rediscovery of these brick facades in architecture.
The wolf brick is said to have been used as a musical instrument.
future
Today there are a multitude of materials for modern pitched roofs that are suitable and have proven themselves for roofing. The clay brick still has a special position, as the manufacturers claim.
In addition to covering with clay roof tiles, concrete roof tiles, bitumen roof shingles, natural stone (e.g. slate), wooden roof shingles and metal roof tiles as well as large-format roof panels such as fiber cement sheets and metal profile sheets ( corrugated sheet , trapezoidal sheet , roof sheets with an embossed roof tile profile ) are processed. Modular panels have the advantage that they are light and, depending on the material, can be weather-resistant. They have a lower dead weight than classic roof coverings and must be screwed onto a formwork to be safe from wind suction.
In 2016, SolarCity and Tesla announced that they would be offering roof tiles with integrated photovoltaics , which thus form the entire roof surface and replace traditional roofing.
Manufacturer
Wienerberger (Austria) is one of the world's largest manufacturers of roof tiles . The largest manufacturers in Germany are Creaton , Braas and Erlus . In addition to these large manufacturers, there were many medium-sized brick manufacturers, but their number is declining. These include Gebr. Laumans Ziegelwerke and Dachziegelwerke Nelskamp .
All manufacturers are organized in the Federal Association of the German Brick and Tile Industry. The federal association is divided into the professional associations North, Northwest, Southwest, Brick Center South and the Bavarian Brick Industry Association.
See also
literature
- F. Engel: The construction. Paul Parey, Berlin 1885.
- Illustrated construction lexicon. Otto Spamer, Leipzig 1883.
- Elke Herbst: roof tiles. Rudolf Müller, Cologne 1997, OCLC 246449054 , (DDH edition).
- Krolkiewicz / Hopfenperger / Spöth: The maintenance planner . Haufe Verlag, Freiburg 2009, ISBN 978-3-448-08794-9 .
- Hans Jürgen Krolkiewicz: The sloping roof. In: db deutsche bauzeitung. 2/86, Deutsche Verlags-Anstalt, Stuttgart.
- Hans Jürgen Krolkiewicz: Roof tiles. History of building materials. In: building material technology. Gert Wohlfarth, Duisburg 2003, ISSN 0721-7854 .
- Hans Jürgen Krolkiewicz: The roof tile - a historical consideration. In: DDH Das Dachdecker Handwerk. Rudolf Müller, Cologne 2004/2005, ISSN 0172-1003 .
- Willi Bender: Lexicon of bricks. 2nd Edition. Bauverlag, Berlin 1995, ISBN 3-7625-3156-0 .
- M. Kornmann and CTTB: Clay bricks and roof tiles, manufacturing and properties. LaSim, Paris 2007, ISBN 978-2-9517765-6-2 .
- Karl-August Wirth: Feierabendziegel (Feierabendstein) . In: Real Lexicon on German Art History . Vol. 7, Col. 1000 f.
- Zi International - Brick Industry International. Bauverlag, Gütersloh, ISSN 0341-0552 .
- Zi yearbook. Bauverlag, Gütersloh, ISBN 978-3-7625-3625-3 .
Web links
- Archive of historical roof tiles approx. 250 manufacturers, approx. 750 catalogs / publications and almost 15,000 scans (5.3 GB of images).
- Arbeitsgemeinschaft Ziegeldach eV , with interesting articles on engobes, aging behavior, steamed bricks, etc.
Individual evidence
- ^ Stefan Hesse: Roof tiles as a source of cultural and historical information. In: Soester contributions to archeology. Soest 2006 (pdf; 1.88 MB).
- ↑ After-work bricks : Gestelte Ziegel , Helmut Herbst / Susanne Jenisch, 100-page exhibition catalog of the Museum Waiblingen, 1988.
- ^ Composition of roof tiles. In: braas.de. Retrieved December 2, 2017 .
- ↑ Roof tiles - composition and manufacture. Roofers Guild Braunschweig, accessed on December 2, 2017 .
- ↑ Detailed information about damped roof tiles at the engineering office LKG ( Memento from April 20, 2014 in the Internet Archive )
- ^ History. (PDF; 1.8 MB) Detlef Stauch, W. Jaegers, accessed on February 7, 2013 .
- ↑ Günter Neroth, Dieter Vollenschaar (ed.): Wendehorst building materials science: Basics - building materials - surface protection. 2011, p. 507.
- ↑ Instructions for training apprentice roofers. Reich Association of the German Roofing Trade, Berlin 1926/27
- ↑ Elon Musk & SolarCity CTO Peter Rive Announce “Solar Roof” (Not “Solar On The Roof”). In: CleanTechnica. August 12, 2016. Retrieved August 26, 2016 .
- ^ Federal Association of the German Brick and Tile Industry eV In: ziegel.de. Retrieved December 2, 2017 .
- ^ Members - Fachverband der Ziegelindustrie Nord eV In: ziegelindustrie.de. Retrieved December 2, 2017 .
- ^ Fachverband Ziegelindustrie Nordwest eV In: ziegel-zentrum.de. Retrieved December 2, 2017 .
- ^ Ziegel Zentrum Süd eV In: ziegel.com. Retrieved December 2, 2017 .
- ↑ Member organizations and links - BZV. (No longer available online.) In: ziegelindustrieverband.de. Archived from the original on February 28, 2018 ; accessed on December 2, 2017 .