Cob is one of the oldest forms used for construction. Remains of cob structures been found in Afghanistan, North Africa and the Middle East with structures dating back as far as the 11th century. More recent cob structures have been found in Cornwall, Devon, Brittany, Wales and North Africa, with many structures, as old as 500 years, found intact.
Cob is made from mixing clay soil with sand, straw and water. Oxen, cattle or humans then walk or dance over the mixture, working it together and helping the binding process. The mixture is then formed into cobs or little balls and added to the structure. This process is repeated again and building up the walls to a thickness of 24 inches or 600mm. The lintels for the doors and windows are inserted as the building goes up and time is needed for drying before the cobbing can continue.
Because of the breathable nature of clay, the straw does not decay over time and allows the walls to dry out once they become wet. A large overhanging roof helps provide a cover for the walls and extends the durability of the walls.
The simplicity of the build allows you to keep adding and removing cob to the walls, in order to achieve the desired shape and texture. Cob is also very easy to repair; when cracks appear they can easily be repaired using more cob.
Alternative paints can be used on the dried wall to achieve the finish you want but chemical paints are not suitable when building in cob. Clay needs to be able to breath in order to self-regulate its moisture and chemical based paints stop this from happening.
Cob House Performance Report - http://ecosenseliving.files.wordpress.com/2011/09/science-research-report_sept_1.pdf