RIBA Core Curriculum
- Building conservation and heritage
- Design, construction and technology
- General Awareness
Clay is a highly versatile and durable construction component that alongside stone and wood, is one of the oldest and most influential building materials on earth. This course looks at the history of clay in roofing and how this impacted and shaped modern roof tiles. The manufacturing process, roofing legislation and the different types and formats of clay tiles are also considered.
In this section
- Clay tile use in Britain
- Technological impacts on roof tiles
- Modern clay roof tiles
In Britain, tile making stood still after the Romans had departed, until monasteries began to develop facilities to make them.
Monasteries reintroduced tile making into Britain, for their own projects and initially they retained the Roman tile style. However over time there was a shift in favour of the smaller and simpler plain tile.
This changed enabled plain tiles to become more fashionable and widespread throughout Britain for a wide range of buildings.
As plain tiles became more and more dominate as the choice for roofing buildings in Britain, the problem of quality increased dramatically. Originally, the quality and size of plain tiles was so variable that it caused a major problem, to such an extent that royal intervention was deemed necessary to try and resolve the crisis.
In 1477, Edward IV decreed that plain tiles should be a fixed size of 10½ x 6¼ x 5/8″. This has evolved into 10½ x 6½” plain tile still in use today.
The standardisation of clay plain tiles was effectively one of the very first British Standards.
Edward’s order also required that the clay be dug or cast before 1st November. Between November and the beginning of February, the clay was required to be turned or stirred before February and could not be used to make tiles before March.
This was to ensure that the material was properly seasoned, which was important to prevent cracking and deterioration when exposed to high temperatures.
British tile makers discovered, long after the Greeks, that firing provided much greater durability properties and added a fireproof resistance.
The early kilns were stacked with tiles and then the top was sealed to keep the heat in. The tile maker would judge the temperature of the kiln by walking barefoot up and down on the top.
The Spanish tile introduced the over and under concept to the Netherlands and influenced the designs of Dutch tiles
However, the Dutch innovated and progressed the idea further to produce a single tile, based on the style of the Spanish Under and Over tiles, that combined the two key elements.
Using a single tile, the familiar pantile shape, was much more efficient to install, which saved time and money, reducing costs. This played an important role in making the pantile so popular that it is one of the most used tile styles in the world.
Dutch tiles first came to the UK as ballast in trading ships on their homeward journeys in the 16th century.
This is largely why pantiles are predominantly found around the eastern coast of England and Scotland, as well as to some degree in and around Bristol, which was a major port in the 16th and 17th centuries.
In 1666 the Great Fire of London, which started at King’s bakery on Pudding Lane near London Bridge, raged for four days and destroyed more than half of London. Tens of thousands of private residences along with the majority of civic buildings were destroyed, although miraculously only six people died.
As a result of the Great Fire of London, thatch was banned in the city of London.
There are early patents for the manufacture of pantiles in England dating back from 1636, but their is no evidence of these in production until 1701.
Daniel Defoe, most famous for his novel Robinson Crusoe, had a varied life and career as a trader, writer, journalist and spy. Records suggest that he was also the first person to produce pantiles in England, at Tilbury in Essex in 1701.
The progression of the kiln
Probably the single biggest contribution to development of clay tiles was the process of firing.
Early coal fired, beehive style, kilns produced varied results as the firing process often intermittent and did not always provide the necessary temperature to produce quality tiles.
Then in 1856 a paper was published by Berlin Master Builder, Friedrich Hoffman and a Viennese City Councillor, A. Licht, describing a continuous firing kiln.
The Hoffman kiln was the forerunner of today’s continuous tunnel kilns and meant that round the clock production was not dependent upon weather conditions
Today, India holds the record for the longest tunnel kiln, which according Guinness World Records measures 720 Feet (219 Meter 45 in) and can reach temperatures of up to 1300 degrees Celsius.
The Industrial Revolution opened up opportunities for mass markets production. Raw materials and finished tiles were transported over longer distances, first by water, and then later by rail.
Steam power was introduced to drive pug mills and other machinery, such as extrusion machines.
However, despite the technological advances, working conditions were often poor and children were routinely employees to carry out tasks such as carrying clay from the mills.
Machine made clay roof tiles
In terms of roof tiles, the modern style is considered to be interlocking and machine pressed. Machine extrusion and pressing ensures that less air is used in the production process, which results in a higher density, more durable tile.
Three French brothers called the Gilardoni patented the first machine-made interlocking tile, which was developed in Alsace in 1855.
This was followed in 1881 by a similar tile manufactured by Wilhelm Ludowici in Italy. Ludowici is now one of the USA’s biggest producers of clay tiles.
The Gilardoni tile was the forerunner to today’s modern machine made tile. The differences between the early designs and the contemporary versions are that precision engineering enables less material to be used in the production process, but due to the design improvements, modern tiles are much stronger and more durable than there historical counterparts. Various interlocking designs have evolved over time, each one looks to improve the performance against the elements, this along with new larger nibs make the tiles more efficient and easier to install.
From the 17th century onward, the Somerset area become a thriving centre for clay bricks and tiles. Somerset makers, near Bridgwater, were responsible for developing the large Double Roman style tile, which is still found in the area.
The Double Roman tile is an evolution of the original Roman Tegula and Imbrex tiles, combining both parts in to one single tile, just as the Dutch had done in the 14th century with Spanish Under and Over tiles.
Numerous small manufacturers in the Somerset region produced the Double Roman style of tile until the 1950’s, however, they were never able to improve the quality of their products enough to match the consistency of the newer concrete tiles. This was partly because of the type of the local clay, and partly because the “flat firing” technology that was to appear in the 1970’s was not yet available to them.
It wasn’t just Somerset and the Double Roman tile that was effected, the decline of clay tiles was so widespread by the 1950’s the British clay pantile industry had all but disappeared. The reputation British clay pantiles was shattered by an inability to keep pace with demand from a booming housing industry, combined with variable product quality, which led to some tiles becoming susceptible to frost damage.
It was only in the 1970’s that the renaissance of the clay tile industry got under way. New French technology for computerised kiln firing and automated handling was developed, and this, together with German machine pressing technology allowed clay tiles to be made much more efficiently.
The shape of the tiles became more regular, they could be made larger, they were cheaper, they no longer suffered from frost problems, and their supply was more reliable since they no longer required drying in open sheds at the mercy of winter frosts.
By the 1990’s there were only seven clay tile manufacturers listed throughout the whole of the UK. Demand for clay was depressed to such an extent that it represented just 5% of the pitched roofing sector at it’s lowest point, but then in 1995, demand started to slowly increase year on year.
The revival of clay was due to a variety of factors such as a renewed interest in vernacular housing design. The greater prominence for the use of traditional building materials and an increased emphasis on overall quality and aesthetics.
Clay as a material naturally wants to twist so historically manufacturers had a challenge to tame the clay. However, modern processes such as “flat firing” now produce tiles of complete consistency, eliminating problems such as distortion and twisting.
Using modern production techniques, colours and shapes are consistent, and tiles are rapidly produced and distributed around the world.
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