Bricks
The entire gate complex was built of bricks baked and fired in a kiln. After the excavation in 1899, thousands of brick fragments were transported to Berlin where they were painstakingly reassembled.
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The journey of tiles through history
What do the ancient Romans have in common with today’s private home builders? Their preference for tiles, perhaps? Since antiquity, tiles have been used to decorate and protect buildings. Throughout history, tiles have had an influence not only on architecture and buildings but also on the construction industry. New developments in tiles also brought about new bonding techniques. Let us embark on a journey through the history of tiles.
#1
The tiles of Babylon: fired and bonded with asphalt
With stunning reliefs featuring bulls, lions and mythical creatures on a deep blue background, Babylon’s Ishtar Gate continues to fill the beholder with awe today as it did in the past.
The animal depictions on the Ishtar Gate symbolize the main deities of the Babylonian religion. The bull stands for the weather god Adad, while the mythical creature Mušḫuššu represents Marduk, the god of fertility and the chief god of the city of Babylon.
Built during the reign of Nebuchadnezar II (605-562 BCE), the Ishtar Gate is one of the oldest examples of early tile art used in architecture. The gate was part of an eight-kilometer-long double wall around the center of Babylon and played a part in processions intended to demonstrate the power of the king. Monumental in size, with its bright colors and magnificent animal reliefs, the Ishtar Gate would have surely captivated the onlooker back then as much as it still does to this day.
Today, this marvelous piece of history is on display at the Pergamon Museum in Berlin where it was restored with great care using the original clay bricks.
A look at the technology behind the art of tiling in Mesopotamia
Joints
The joints between the bricks were filled with thin “mortar layers” of heated natural asphalt, which was allowed to flow into the cavities between the bricks and ensured that the bricks bonded firmly as they cooled.
Ceramic tiles
The ornamentation consists of deep-blue and orange-ochre glazed, relief-like ceramic tiles that were first baked and then coated and glazed with a viscous, paste-like glazing mass. Around a tenth of the tiles are original fragments from the Babylonian period; the remaining were added during the reconstruction of the gate in 1928.
Restoration
Fluctuations in humidity had an impact on the tiles whereby cracks appeared in the glazing and some fragments even chipped off. During restoration work, polyvinyl butyral dissolved in ethanol was injected into the cracks to strengthen and fix the glazing.
#2
Roman mosaic art: durability with volcanic ash
Tiles saw an incredible boom in the Roman Empire: villas, public baths and thermal baths were decorated with elaborate mosaics made of clay tiles.
One of 15 mosaic floorings in the House of Dionysus at the Kato Paphos Archaeological Park on Cyprus, built at the end of the 2nd century AD.
The mosaic technique with its tiny stones, known as tesserae, allowed the craftsmen to create stunningly detailed patterns, including depictions of animals, portraits and mythological stories. It is interesting to note that, prior to commencement of work, the finished patterns were presented as images for the client to choose from.
In addition to decorative purposes, mosaics also had practical functions: they protected the flooring and in some cases even served as an early form of underfloor heating.
A look at the technology behind Roman mosaics
In order to prepare the surface for the final floor, the ground was first leveled and covered with a layer of tesserae and coarse lime mortar. The next step involved a second layer of tesserae and fragments of clay mixed with lime, followed by another thin layer of lime. The tesserae were placed in the moist lime. The addition of volcanic ash made the lime mortar particularly durable.
Local stones, imported marble or even colored glass were used to make the tesserae. They are approximately 1 cm3 in size. Finally, marble dust, sand and lime were rubbed onto the surface to make the finished mosaic even more resistant.
A closer look at high-performance mortar used in antiquity
The fact that a large number of Roman mosaics have stood the test of time is partly due to a special mortar which was made extremely durable by adding volcanic ash.
Adding seawater to a mixture of lime and volcanic ash results in a material known as pozzolana, which can be mixed to form a kind of concrete. During the hardening process, the volcanic ash reacts with the lime-water mixture to form a calcium aluminum silicate hydrate. At the same time, stratlingite, a plate-like mineral that forms densely interlocked structures and fills the transition areas between the cement mortar and the added materials, is formed. Once the pozzolana has hardened, almost all the cracks are tightly sealed and the mortar is impervious to water. It can even withstand earthquakes without damage.
Today, pozzolana is making a comeback and is being used to lay natural stone tiles in outdoor areas. In what are known as pozzolanic cements, the proportion of Portland cement is reduced by up to 50% and replaced by a high volume of pozzolana, for example crushed tuff (trass). As a result, pozzolanic cements have a considerably lower CO2-footprint than plain Portland cements.
#3
Moroccan tile art – setting the right tone
Hardly a traveler in Morocco will be able to miss them: magnificent ornamental mosaics that adorn mosques, palaces, madrassas and other buildings.
Bou Inania Madrassa in Fez, Morocco, built between 1350 and 1357 as a university and mosque, features elaborate ornamental mosaics made of zellige tiles. The mosaic tiles were chiseled into shape by hand.
Zellige tiles, undoubtedly the symbol of Moroccan design, are instrumental in creating these splendid mosaics. Zellige is derived from the Arabic term “al zulaycha” (sometimes written as zillij or zellij), which means “polished stone”. The art of colorful ceramic mosaics took roots as early as the 12th century and continues to thrive in traditional craftsmanship in modern-day Morocco.
Zellige tiles are also very popular in modern interior design. In contrast to mass-produced goods, imperfections are what make zellige tiles so appealing. Made by hand, no two tiles are the same. In fact, uneven surfaces and varying color nuances are what make them so desirable. Zellige tiles are suited chiefly for walls. High mechanical stress and frost can severely damage the delicate tiles.
A look at the technology behind zellige tiles
Zellige tiles are made from natural clay that is mixed with water and kneaded, shaped by hand and dried in the air. After the first firing, the glazing is applied by hand and the tiles are vitrified in the kiln, thereby creating a shimmering, pearl-gloss finish. In the final step, the glazed tiles are cut into shape. Beveled edges, which allow the tiles to be laid almost seamlessly, are a typical feature of zellige tiles.
#4
Azulejos – well settled in Portugal and Spain
Muslim rulers introduced the art of color-glazed tiles from North Africa to the Iberian Peninsula in the 14th century. With “azulejos”, the Spanish and the Portuguese laid the foundations for the art of tiling across Europe.
Apart from their visual appeal, these tiles also had a practical function: they were used to protect buildings from heat, moisture and – in coastal regions – from aggressive salty air. Thanks to the fired glazing, the tiles were water-repellent on the outside and gave the impression of being made from porcelain. At the same time, the base material and reverse of the tiles were porous, which allowed the ensuing capillary force to form a secure bond with the plaster.
#5
Exploring new avenues Dutch style
As a seafaring nation, the Netherlands played a major role in making tile art popular across Europe. In the 16th century, the art of faience reached new heights in Holland: prefired ceramic tiles were coated with a white tin glaze, painted with a brush after drying and then fired a second time.
Delft tile decoration was also inspired by Dutch and seafaring motifs.
This made pictorial motifs possible, which often extended over several tiles. Prominent Dutch faience factories were established in Amsterdam, Delft and Utrecht. Appreciated for their typical features such as the conventional size of 13 x 13 cm, the elaborate traditional painting and fine hairline cracks in the glazing, Delft tiles are renowned to this day.
Delft tiling art had its heyday between 1580 and 1850: hand-painted with a brush, the tin-glazed tiles had a porcelain-like finish. After 1625, Delft artisans only used the famous blue-and-white color scheme which was inspired by designs from China that were in vogue at the time.
A closer look at the invention of Portland cement
1824 saw a revolution in tile adhesives: English bricklayer and businessman Joseph Aspdin was the first to burn clay and limestone to form cement. He called his invention “Portland cement” – by analogy with the Portland stone that was quarried on the Isle of Portland in Dorset. Aspdin thus paved the way for modern-day cement.
His compatriot Isaac Charles Johnson achieved a significant advancement in the process in the 1840s: he fired clay and limestone at higher temperatures, almost to melting point. This produced small, spherical pellets, known as cement clinker. When ground, the pellets produced a powdery cement that could be used as a concrete binder by adding water. The result was a fast-drying, high-strength and durable type of concrete. Johnson’s process has remained unchanged and continues to be implemented to produce Portland cement to this day.
#6
Terracotta tiles: earthenware in a cozy bed
Ceramic tiles made of fired clay have been in use since around 4,000 BCE. Ancient Egyptians, Romans and Babylonians used them as decorative floor coverings. Terracotta tiles are popular even today.
Unglazed earthenware tiles in natural, earthy, reddish hues – the term terracotta is derived from the Italian terra cotta, which literally means “baked earth”. Terracotta tiles are mainly produced in the Mediterranean region, where they are still widely made by hand using exclusively natural materials.
A look at the technology behind terracotta tiles
Terracotta tiles are popular not only due to their warm colors and visual appeal but also their special properties: they are warm to the feet, absorb sound and allow vapor to permeate. Good thermal conductivity also makes them the ideal floor covering for underfloor heating.
Open-pored and very porous, terracotta tiles also absorb a lot of water. The conventional medium-bed or thick-bed method is particularly suitable for tile-laying: the tiles are laid in a bed of cementitious mortar and then moved to the proper position. Irregularities and different tile thicknesses can thus be evened out. The cement penetrates into the pores of the tiles and forms an anchor between the tile and the mortar. It is necessary to seal the surface after laying, as the porous tiles are extremely susceptible to staining.
#7
Fine, finer, porcelain stoneware: we’re going to stick with polymers
The tile sector underwent a true revolution in materials shortly before the turn of the millennium: in 1980, the fast-firing roller hearth kiln process, a firing method for the profitable production of porcelain stoneware tiles, was developed in Italy.
Although the reddish-brown porcelain stoneware, also known as Böttger stoneware, had already been invented in 1706 by Johann Friedrich Böttger and Ehrenfried Walther von Tschirnhaus, it was the new firing process that gave porcelain tiles a boost: by 2024, 58% of all tiles worldwide were made of porcelain stoneware.
A closer look at the transformation from the thick-bed to the thin-bed process
The polymer modification of tile adhesives also revolutionized the laying techniques. Since the 1950s, we have been observing a switch from the thick-bed to the thin-bed method, whereby the tile adhesive is now only applied to the tiles in very thin layers – a process that reduces material usage and CO2 emissions and makes the tilelayer’s work much more efficient.
Click here to find out more about the polymer modification of tile adhesives.
A look at the technology behind porcelain tiles
There are many reasons for this triumph: porcelain tiles are robust, hard-wearing and durable. Thanks to their low water absorption of less than 0.5%, they are also ideal for outdoor use. The low porosity of the tiles, however, also placed new demands on the tile adhesives: conventional sand-cement mixtures are pushed to their limits on smooth surfaces. Only the addition of polymer binders can improve adhesion and create a flexible bond between the substrate and the tile. WACKER had already produced dispersible polymer powders on an industrial scale in the 1950s and was thus an important part of this development.
#8
Large, larger, XXL: special adhesives for the big job
Large-dimension tiles are in demand across the world: in Europe and the United States, more than 84% of tiles are already larger than 30 x 30 cm, while 60 x 60 cm is the new standard size in China and India.
And there seems to be no limit to the dimensions: porcelain tiles up to 150 x 300 cm are no longer a rarity. As an inexpensive alternative to natural stone, they make walls and floors look as if they have been covered with a single piece. We need to bear in mind, however, that the larger the dimensions, the greater the challenges for tilelayers and materials.
A closer look at back-buttering
The size, low porosity and often highly textured reverse of XXL tiles makes a technique called “back-buttering” necessary: the tile adhesive is applied not only to the wall but also on the reverse of the tile at the same time. This “contact layer” ensures a permanent bond between the tile and the substrate.
A look at the technology behind XXL tiles
XXL tiles have some special characteristics that need to be taken into account during tile-laying: as they are generally made of porcelain stoneware, they have a low water absorption capacity of less than 0.5%. At the same time, they can be quite heavy due to their size: even a 120 x 120 cm tile can easily weigh 20 kg. Apart from that, large-size tiles are never completely flat, so any unevenness must be compensated for by the tile adhesive.
Click here to find out more about laying XXL tiles and the requirements for tile adhesives.
It all depends on the tile adhesive
Adhesives with EN classification C2TES1 or C2TES2 are particularly suitable for XXL tiles. These adhesives possess the following properties:
Tensile Adhesion Strength
Large-format tiles are heavy. For a really secure bond, they require a Class C2 adhesive.
Flexibility
Highly flexible tile adhesives can compensate for movements of the substrate and can absorb shear forces. Highly flexible tile adhesives are rated “S1” and “S2” in the European standard.
Open Time
An adhesive applied to large areas of substrate and the backs of the tiles should have an open time of at least 30 minutes. Adhesives with an extended open time are rated “E” in the European standard.
#9
Glass and metal tiles? Polymers by all means for greater diversity
Modern tiles come in all shapes and sizes. Never before have we seen such a diverse range of products. Today, in addition to porcelain stoneware, porcelain and terracotta, we even have tiles made from glass or metal.
Glass tiles are particularly suited for swimming pools, wellness resorts and spas. They are robust and can withstand the high water pressure in swimming pools. Furthermore, thanks to a wide range of colors and transparency grades, glass tiles also create a shimmering effect. Glass tiles are also becoming increasingly popular in bathrooms, for example as a design highlight in a backsplash.
Tiles made from bronze and other metals are well suited not only for homes and domestic purposes but also for upmarket hospitality, healthcare facilities and for store design. In addition to presenting a clean and contemporary look, metal tiles are extremely durable, easy to clean and hygienic.
A closer look at glass and metal tiles
As in the case of porcelain stoneware tiles, glass and metal tiles have a very low porosity and a very low water absorption rate of less than 0.5%. Polymer-modified high-performance adhesives are indispensable for glass and metal tiles. Such adhesives contain polymeric binders that create a glue-like bond in the hardened mortar. These “polymer bridges” ensure a high bond strength between the tile surface and the adhesive under all climatic conditions. As a general rule: the lower the porosity of the tile, the higher the polymer content in the adhesive should be.
Apart from tensile adhesion strength, polymers also give the adhesive mortar an additional superpower: flexibility. A polymer-modified tile adhesive acts as a bond between the tile and the substrate and absorbs impact energy, for example shear forces.
Click here to find out more about the polymer modification of tile adhesives.
#10
The next generation of tiles: the journey continues – and we want to be a part of it
Today’s consumers enjoy an incredible range of products: tiles are available in virtually every size, shape and pattern. And there is no limit to the ingenuity of manufacturers. Apart from aesthetics, sustainability too plays an increasingly important role.
In this context, we can already boast several pioneering innovations: for example, 3D-printed tiles from sustainable materials such as sawdust and Chardonnay grape skins that can be used for greening; or specially coated ceramic tiles that can capture pollutants from the air.
Such examples show that there are no limits to the evolution of tiles. We at WACKER want to be part of this journey. Our extensive know-how and expertise in the polymer modification of tile adhesives allows us to come up with the perfect formulation for every kind of tile. We are committed to continue being a strong partner and pioneer and taking a bold step into the future.
What will tile-laying be like in the future?
Click here to find out more about the latest tiling trends and techniques.
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