Cob is a natural building material that is made from clay soil or subsoil, water and straw which is used to build cob walls or cob houses. This type of building material has been used for centuries which has been around the longest since the 13th century. A cob wall would be constructed off a stone plinth as the base of the cob must be kept away from ground level to prevent the likelihood of saturation. Clay soil would be flattened out on the ground with a bed of straw on top which the tracks of a machine compacts down the two materials. The mixture is then folded which ensures the straw is not broken down. A layer of cob is placed onto the stone plinth and flattened by trampling the cob and compacting it down with the heals. The layer of cob needs to be dried before the next layer of cob can be placed on top. Once the wall has reached the desired height, shaping of the sides will take place.
STRONG & DURABLE
When materials are mixed correctly, cob is as strong and durable as concrete requiring no extra energy for production other than manpower to produce the cob mixture. It is also strong enough to be earthquake proof as the house or walls act as a monolithic piece that does not cause cracks as the ground moves below. There are benefits to using cob over concrete such as cob being the most sustainable form, recyclable and most affordable way of building having zero embodied energy. Cob material is also very breathable and does not used any harsh chemicals or additives making the environment very healthy to live in as the walls will not dampen. Another benefit to using cob is that it does not wash away in the rain as it is very resistant to weathering. However, it is best to avoid too much exposure by using the “boots and cap” strategy which includes a wide roof over to protect the top and the sides of the walls.