Embracing the Regionality of Clay

By Annette Forster – Marketing Director at Wienerberger

Do you ever wonder what shapes our built environment? Even those of us who take the most passing interest cannot help but notice the wide variation of building materials and style. Britain is a small island, yet regional differences are diverse. Our long-standing fascination with clay, a natural building material, stems from how, through its evolution, it has shaped the buildings and landscape of Britain. Alongside stone and wood, clay is one of the oldest building materials on earth, with roof tiles and bricks preceding the industrial revolution, the railways and even the canals. It forms an essential part of the load-bearing structure of the majority of buildings we live and work in today. 

The Beauty and Benefits of Clay

Clays, often referred to as ‘heavy clays’, is the term used to describe clays and shales used in the manufacture of structural clay products, such as facing and engineering bricks, pavers and tiles for roofing and cladding. The ‘heavy’ here arises from a description of the products and not the raw materials. Such products are made throughout Britain and the location of the industry tends to reflect the distribution of the principal brick clay reserves. Heavy clays are fine-grained sedimentary rocks of different geological ages, sources and compositions that occur extensively throughout Britain. These range from relatively soft, plastic clays to hard mudstones. Their ceramic properties, which are related to their mineralogical composition and physical properties, particularly grain size, are critical to determining their suitability for the manufacture of structural clay products. These properties often dictate the forming method of the clay (the process prior to ring in which the ware is shaped) and also the final properties of the red product. These red properties include strength, water absorption and frost resistance, and therefore durability and long-term performance in service. Importantly, they also affect aesthetic appearance, such as colour and texture, providing greater choice and style for architects and developers.   Clay is a versatile and durable construction material and one of the most visible components of the built environment. In addition to clay’s functional use, it makes an important contribution to local architectural styles in our cities, towns and villages.    A wide range of clays are used in the manufacture of structural clay products thanks to extensive distribution throughout Britain. Most clays are red firing and this familiar colour is due to the presence of iron minerals in almost all clays. However, the presence of carbonate minerals, such as calcite and dolomite, can produce paler colours. Carbonate minerals must be in a fine-grained form as coarse carbonates may lead to a problem known as lime blowing (‘blowing’ of the surface of a brick or tile due to the expansion of hydrated nodules of lime).    Buff or cream-coloured products are produced by using fireclays with low iron content. Another key factor in determining the red colour and other physical properties of bricks and tiles, is the atmosphere within the kiln. Most red-firing bricks and tiles are red in an oxygen-rich atmosphere, whereas yellow bricks, such as London stock bricks, are made from a mixture of clay and calcium carbonate (chalk) and red in a low oxygen reducing atmosphere. Similarly, the Staffordshire blue brick is made from local Etruria marl which contains a high proportion of iron-bearing minerals. When red at a high temperature and in a low oxygen reducing atmosphere, these minerals take on a deep blue colour, producing a brick with a very hard, impervious surface with high crushing strength and low water absorption.

Regional Brick Choice

Brick choice is hugely influenced by the geographical location of the project as well as the style of house being designed, so product requirements vary significantly. The most popular types of bricks for self-build projects tend to be the more traditional stock bricks with a creased texture. They are widely used when typically a more ‘olde worlde’ look is required and Wienerberger is the market leader for such products. However, there is also a trend towards more contemporary bricks where people are looking to achieve a more modern, avant-garde appearance. These tend to be more precise bricks with crisp arrises rather than the softer, textured products. They also tend to move away from the traditional UK format of 215x65mm towards longer, thinner formats.    Wienerberger created a special Coronation Medley for the ITV soap opera Coronation Street — an exact match to the original Homestead Medley manufactured at our Denton factory in the 1980s and ’90s. The tones and textures were chosen to match the traditional red brick commonly found in the Manchester area.   

Regional Roof Choice

The use of clay roof tiles in the UK can be traced back as far as the Romans, who used ‘under and over’ tiles. These are flat trays with cylindrical overs covering the joints, hence the term ‘double roman’ for modern interlocking tiles, which mimic the appearance of under and over tiles.    Plain or ‘flat’ clay tiles came into general use around the 12th or 13th century, and became the roofing material of choice in London following a royal decree from King John in 1212 prohibiting the use of thatch. Since then, the material has never been out of production. Plain tiles are still manufactured to the dimensions standardised by King Edward IV in 1477 (10 1/2 x 6 1/4 x 5/8 inches).    Overlapping tiles, such as clay pantiles, were introduced into Britain in the 17th century in regions engaged in trade with Holland. This is why pantiles are found in east-coast regions, from Scotland through to Yorkshire, Lincolnshire and Nottinghamshire. Similar regional distinctions exist in brickwork — yellow bricks in the south, blue tones in the Midlands and a blanket covering of red brick in the north. But how can we explain the origins of these regional distinctions?    The regional distinction lies in a combination of geography and geology. With no way of transporting heavy goods, early clay tiles and bricks were red in kilns local to the areas where they would eventually be laid. Naturally, as a raw material, the attributes of the raw clay varied from region to region. These geological dfferences came to the fore in the firing process, creating distinctive blends of colours and textures that, in turn, became unique to each region.    Sadly, following the industrial revolution and the post-war building booms, much of this regional identity was lost. Between the world wars, when demand for new homes was high, UK manufacturers struggled to cope with the demand for materials, and components were imported from Europe. Thousands of homes were roofed using European clay tiles, with some only now undergoing refurbishment and re-roofing.    Concrete tiles dominated when a huge rehousing programme started after the second world war, and by the 1950s British clay roof tile production had all but disappeared, with just a handful of factories struggling on using out of date production methods. The result was that our houses became more and more homogenised.    In the 1980s great advances were made in clay technology. Investment in large-scale clay tile factories in Britain led to a clay tile resurgence that coincided with a boom in slate. This created a renaissance in the use of natural roofing materials.   Ironically, the design of clay roof tiles has now come full circle — concrete profiles were originally copies of the classic clay tile shapes. But now, modern technology is enabling clay tile manufacturers to create classic models incorporating the very features that make concrete tiles so easy to install. At Wienerberger, our New Generation Sandtoft clay tiles have an open gauge, allowing roofers to easily set the gauge on the roof without the need for cutting or short courses.    The resurgence of clay tiles in the UK is now well underway, offering the beauty of a natural material combined with affordable installation costs, long-term durability and a colour that’s guaranteed not to fade.   - Originally featured in Homebuilding & Renovating Magazine (April 2016)

Annette is the Director of Marketing at Wienerberger and a lead on the Brick Development Association and Construction Products Association. Wienerberger, the world’s largest producer of bricks and Europe’s biggest producer of clay roof tiles, has four showrooms and 14 factories in the UK. Its range includes brands such as Terca, Porotherm, Sandtoft, Keymer and Penter.

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