Across the globe earth has been used as a building material because it is readily available and exists wherever people have dwelt throughout the ages. Thus, throughout the world you can see examples of earth in the construction of homes, typically the adobe houses made from sun dried bricks. however is an English term that refers to the use of mud for building and does not involve the use of any forms or bricks or wooden structures of any sort.
The actual start of cob buildings in England is uncertain but likely they were gaining in popularity in the 13th century when it may have been discovered that as other materials decayed or fell away the mud mixture used to support them remained intact and stable. Thus, the cob alone could be used to build homes and thus simplify the procedure. The popularity of the cob homes was no more apparent than in the south west of the country and in Devon in particular. The sandy clay of the region leant itself to this type of construction and the scarcity of other building materials, such as wood and stone would have made this an attractive option.
The English cob is made from clay-based soil mixed with straw, water and often sand or other crushed material like flint or shale. Traditionally the desired mix is achieved by various percentages of each element and the mixture being combined and prepared by animals that would trample over it or by human feet and shovels. The initial foundation of the building would be built of stone and then subsequent layers of cob added and trodden into place at a rate of about 18 inches height a day. Once one complete layer had been trodden into place it had to be left to dry for several days and then the process repeated. The cob would be trimmed with shears to achieve a straight and plumb wall which could be anywhere between 20 and 36 inches thick.
The building thus progressed, and windows and doors could be built in as the walls grew or cut out at pre-marked spots at a later stage. Originally the cob homes were built by poor farmers who had little choice but to use resources from the land. Working as a collective they could combine their efforts to produce homes in one season. In this way homes could be constructed and thatched before the winter months and then left to dry thoroughly before being stuccoed the following year.
Today it is possible to see around 20,000 cob buildings still in use in Devon, homes as well as working out-buildings. Many homes of a grander nature were built in times past, such as Hayes Barton the childhood home of Sir Walter Raleigh. Until brick became readily available this was often the preferred method and the fact that so many of these beautiful buildings still exist today, and in excellent condition, speaks to the amazing hardiness of the natural components and the skill of those early builders!