Sometimes they can be difficult to recognise as they are often covered in coats of lime render or, even worse, cement render, but the thickness of the walls, the good overhang from the roof and the stone plinth at ground level are generally indicators of earthy structures.Cob is normally constructed in lifts or layers. This form of construction can be traced back as far as 1212, although in Devon most of the cob buildings were constructed between the 17th and 19th centuries. Lime renders and mortars were generally used as finishes because of suitability and compatibility with cob, and are still used today for the same reasons. Historically, limestone would be burnt in a simple kiln and, because of the construction of the kiln and the variety of fuels used, the properties could be diverse. These days modern technology ensures that the quality and performance of lime is quantifiable.
There are some very basic dos and don'ts with cob. Because of the very nature of the material it has to retain some moisture but not enough to cause a damp problem, therefore it needs to 'breathe', i.e. to be allowed to dry out when wet and retain moisture when the atmosphere is dry. Lime renders allow the cob to do just this and should not be sealed with silicones and cement renders. The old adage of cob requiring ''a good hat and good boots'' is perfectly true; cob should have a good, tight roof with an overhang of 200mm or more and a stone plinth of at least 600mm provides a good base. Vertical cracking allows moisture to penetrate so should be attended to; stitching with cob or clay tiles can remedy this quickly and effectively in many cases, but it is best to seek professional advice first.
Because of the very nature of building with unfired earth those advising on, specifying and implementing repair techniques should fully understand the composition and construction techniques of cob and earth construction.
Although cob construction is a traditionally regional technique of building with earth, earth building is found globally. Sumita Sinha, a London architect reporting in the Architects' Journal, estimates that one-third of the world's population live in earth buildings and, what's more ... nearly all buildings throughout the world contain some form of earth as a basic ingredient.
Because of the advantages of building with earth - i.e. the material is cheap, transportation is minimal, buildings can be constructed quickly to provide basic shelters in disadvantaged communities - many international new earth building projects are under way using a variety of techniques. In Australia, USA, France, Germany, Norway and other parts of the world there is a lot of rammed earth construction. This technique can create buildings that are safe and durable, and designs that are very desirable, with costs being very competitive with other forms of construction.
Whether you live in a character cottage that requires repair and maintenance or are interested in a contemporary designed building in earth, require advice on self build, funding or any other information on earth building contact the Cob Construction Company.
The team within the Cob Construction Company consists of a conservation architect, other professionally trained earth consultants, academics and skilled crafts people. Working as a team there is joint consultation on site, specifications and application, so that customers are assured of a professional service and high standards of craftsmanship.
The Company's approach to the repair of earth buildings is based upon the philosophy of 'minimal intervention' and a clear understanding of how earth behaves as a structural material. In essence this means that the building's original fabric is retained as much as possible, and other traditional and earth based materials are used where possible and appropriate. It is only by adopting a sympathetic and informed approach that the structural and historic integrity of cob buildings can be properly maintained.
Members of the cob construction team have also had experience in various forms of modern construction techniques, including rammed earth walls, and would be able to offer practical help and advice on contemporary earth building.