Context 143 - March 2016

16 C O N T E X T 1 4 3 : M A R C H 2 0 1 6 ADAM WEISMANN and KATY BRYCE Earth plasters and how to use them Earth plasters (also known as clay plasters) are currently enjoying a revival, for both internal and external use, after a long history in traditional buildings around the world. The resurgence in the use of earth plasters is partly in the form of using home-made, locally resourced materials, and partly due to an emergence of ready to use, pre-manufactured earth plasters from both the USA and Europe. In this article we use the term ‘plaster’ to denote both internal and external work. Earth plasters, prepared at their most basic level, from clayey subsoil, aggregates and a natural form of fibre, would have been the first method of weatherproofing for primordial structures. This would have been due to the abundance of the necessary materials and the special qualities of the clay, specifically its ability to become plastic and malleable when wet, and hard and water-repellent when dry. Earth plasters have been used all over the world, in all climates, since shelter building began. In the UK, earth plasters were routinely used on internal wall surfaces alongside lime, up until the end of the 19th century.Their regular and common use was due to the local abundance of the materials, and the fact that building lime and high-quality aggregates were comparably expensive and sometimes difficult to obtain. Often they were used as an undercoat, to even out the wall surface before receiving a top-coat of lime plaster/ render or limewash. Throughout the rest of the world the use of earth in plasters also has a rich history. In both Africa and the Americas the application of earth plasters on to earth structures was traditionally women’s work. The term enjarradora describes women in the south-west states of America who carried out these earth plaster- ing techniques. Their methods of application and the materials used were highly specific from region to region, and these traditions are still very much alive. In Africa, special relief work and painting carried out in earth plaster on to individual homes (known as litema ) remains a culturally significant way for people to decorate their homes, defining their identity within the wider community. There are many benefits to using earth plasters. They are porous, so they allow a building structure to breathe, acting as a third skin around the building and its inhabitants. Earth plasters have a thirst for moisture. This means that they can regulate levels of relative humidity in the atmosphere.They can safely absorb and hold moisture vapour within their molecular structure when relative humidity levels are high, and release it back into the atmosphere when relative humidity levels drop. As well as providing high-quality internal air for The earth-sheltered building by Glenn Howells Architects at Gloucester Services on the M5 has reinvented what motorway services can be, and how they interact with the local economy, community and food suppliers. It was the national winner of the Civic Voice Design Awards in 2015.The walls are finished with pigmented clay plaster by Clayworks, which helps to regulate humidity. (Photo: Hogyn Lleol, Wikimedia Commons)