Understanding Cob - Great Pictures And How To
Categories: Building Methods
If you have a clay based subsoil (15-25% clay) you are in luck as your home's raw material is below your feet. (You want the inorganic stuff down under the topsoil, no decomposing mulch and micro-organisms.) Mix your clay soil with some water, sand and straw. Mix with your feet, bare or booted, or with any number of mechanical mixers, or an oxen, or for a really large job, use a backhoe. See the ilovecob website for multiple mixing methods.
Before beginning a project it is always a good idea to make a few large practice blocks and allow them to dry thoroughly. These test blocks will show you the best ratio of sand and straw that will work best with your clay soil.
Remember that cob has excellent thermal properties and moderates temperatures, but eventually heat or cold reaches the other side of the wall. Cob's R value, even with extra straw, has never tested better than 1 R per inch, usually it tests much lower. In cold or hot climates you should consider building certain walls in a non-conductive, insulating material such as straw bale. Actually many in cold climates are building double framed walls, cob on the inside with an insulated wall on the outside. A cob wall stores the heat or cold, an insulating material blocks heat or cold from passing through a wall.
Cob home under construction.
Cob bond beam in Michigan. Shovel the cob onto your foundation. Trample with feet. The walls of a cob home are generally 18 to 24 inches thick. The mass will hold heat in winter and the night's coolness in summer. Photo taken by Eva Wimmer.naturalcottageproject.com
Mashing the cob with bare feet on tarps in South Dakota.
There are some earth bags above the rock foundation that the cob is sitting on, I assume they will be covered with cob.
Built by HouseAlive.
In France cob is known as bauge.
In France they use pitchforks (or cob picks) and wear rain boots!