Period character guide: Architectural terracotta

ABOVE (click on gallery image to view larger picture): Terracotta detailing seen on houses in Kensington and Chelsea in London. From the 1860s architectural design drew on Medieval Gothic and Neoclassical styles.

In the late 19th century terracotta clay detailing on houses and mansion flats became the height of fashion. Roger Hunt marvels at the material’s versatility and visits a Hampshire pottery where the hand-manufacturing craft is alive and well today.

For me terracotta is one of those materials that adds magic to a building. Childhood trips to London to visit the Natural History Museum always gained an added frisson when I stared up at the intricate detail and exquisite colour of its terracotta facades. Only later did I learn that the blue and beige colour scheme of the museum was achieved by tinting the terracotta clay with ground slate before it was fired.

Literally meaning ‘baked earth’, terracotta was occasionally used on Tudor houses but really made its mark on British architecture from the 1860s. Produced from moulded clay in a similar way to brick, the individual elements tend to be larger and are of finer quality. Indeed, terracotta is often used within brick built facades to form cornices, quoins and the balusters of balconies to provide contrast and rich ornamental detailing where stone would have proved prohibitively expensive.

Many terracotta elements were hollow, making them relatively light in weight, while the moulding techniques meant that stock shapes could be mass produced, although custom-made elements were individually sculpted and handmade by craftsmen. The material was embraced by the Arts & Crafts movement, notably at the Watts Chapel near Guildford, Surrey, and frequently used in the construction of city mansion blocks of the period. It is sometimes found on quite ordinary homes in the form of plaques and date stones and there are numerous examples of Victorian terracotta gateposts.

Terracotta was particularly useful as a facing material for the new metal-framed buildings of the late 19th and early 20th centuries, such as the London Tube stations of Holloway Road and Covent Garden designed by Leslie Green. In the 1890s glazed terracotta or faience became fashionable because it absorbed relatively less smoke and was easier to keep clean.

ABOVE (left-right): The Victorians preferred entrances to be imposing to denote the status of the family living within. These 19th-century terracotta porches in London are given architectural weight through their formal design; Date stones are often made from terracotta, such as this one in Art Nouveau script, built into a house in the Isle of Wight; Faience window mullions made by West Meon Pottery for a renovation project.

Terracotta revived
At West Meon Pottery in Hampshire Mick Pinner has been producing architectural terracotta since he took over in 1984. Now the work undertaken involves everything from making simple air bricks to highly decorative items such as chimney pots, finials or roundels for major renovation projects.

Some designs are copied from photographs or drawings. Alternatively, a latex cast is taken in situ but, as Mick explained to me, this cannot be used as a direct mould because the clay typically shrinks by 10% when it is fired. This means that, with the aid of rulers and callipers, a scaled up clay master version has to be sculpted by hand which is 10% bigger than the final piece. From this a plaster of Paris mould is made, from which the final items are cast.

According to Mick the majority of the clay used at West Meon Pottery comes from a local Hampshire pit, although white and buff work is made using clay sourced elsewhere. The first stage in preparing the clay is to mix it with water in a large dough mixer. Once it is a sloppy consistency it is filtered through a vibrating sieve to remove pieces of fossils, shells and other debris. The fine mud that results is spread on a drying bed before being mixed with aggregates and minerals. These materials help cut down the shrinkage and warping of the clay when it is fired.

With a consistency similar to plasticine, the clay is carefully pressed into the mould so that any surface bubbles are squeezed out. It is then left until it shrinks back slightly and pulls away from the mould and can be turned out. Some pieces require no further work but generally, to create the desired finish, the surface is smoothed and modelled with a variety of tools including shaped bamboo sticks.

The finished item is then left to slowly dry in the workshop over a period of several weeks before being loaded into the kiln. The firing temperature for different types of clay varies and will have a direct bearing on the durability and colour of the finished piece. At West Meon Pottery temperatures of 1,060ºC to 1,100ºC are typical and the firing takes some 50 hours.

Care and repair
Stonemasons are best equipped to make repairs to terracotta and it is always worth consulting a company specialising in terracotta for advice. If you commission replacement pieces, remember the colour can vary greatly depending on the source of the clay (that of the Midlands is very red, London paler) and firing method used, so request a test sample, otherwise repairs may be conspicuous.

Although terracotta looks strong and durable it is incredibly vulnerable. Stress and movement will cause it to crack while its fire-skin is thin and fragile and, once this is damaged, the softer surface below will quickly erode.

Cracking is particularly likely where hard cement mortars have been used to bed and joint terracotta as they will prevent movement and expansion. Problems also occur where, as was common, terracotta has been fitted to a metal frame or held in place by ferrous fixings as these elements rust and expand. Where new metal ‘anchors’ are inserted, stainless steel should always be used.

When moisture penetrates terracotta it can release salts from within, resulting in efflorescence and frost damage with harmful consequences for the surface, so maintenance of rainwater goods and flashings is vital. Plants easily seed in the nooks and crannies of a terracotta facade and should be removed to avoid damage.

Cleaning terracotta
Paints and sealants applied to the surface of terracotta are likely to trap moisture and inevitably look unsightly. Another problem is dirt. Terracotta soils badly and, as with layers of paint, deposits of grime built up over the years are aesthetically unattractive and may be hiding problems.

Removing paint or dirt is extremely difficult, so always consult a specialist with direct experience of the material. Whatever method is tried, tests should be carried out on a small unobtrusive area first. Even the most carefully controlled methods are likely to cause some damage and may result in bleaching of the surface colour.

Never use abrasives such as wire brushes as they will etch the surface and destroy the fireskin, and beware of water methods as they may release salts resulting in further decay. Always ensure those involved in carrying out the work fully understand the materials involved.

ABOVE: 1 The majority of clay used at West Meon Pottery in Hampshire comes from a local pit, and here potter Mick Pinner digs up. some raw clay to begin the making process. 2 The first stage in preparing the terracotta clay at West Meon Pottery is to mix it with water in a dough mixer. 3 Mick blends the sticky clay with fine aggregates and minerals. These materials help cut down the shrinkage and warping of the clay when it is fired. 4 Once it has reached a consistency similar to plasticine, the clay is carefully pressed into the mould so any surface bubbles are squeezed out. 5 The clay is then left until it shrinks back slightly and pulls away from the mould and can be turned out. 6 To create the required finish, the surface is smoothed and modelled with a variety of tools including shaped bamboo sticks.
BELOW: 7 This latex mould has been cast from an existing decorative roundel in situ. 8 Mick inspects a roundel after firing at West Meon Pottery.

Visit Roger Hunt's website at huntwriter.com

WORDS ROGER HUNT PHOTOGRAPHS ROGER HUNT
Featured in the October 2010 issue of Period Living