Cob is a very old method of building with earth and straw or other fibers. It is quite similar to adobe in that the basic mix of clay and sand is the same, but it usually has a higher percentage of long straw fibers mixed in. Instead of creating uniform blocks to build with, cob is normally applied by hand in large gobs (or cobs) which can be tossed from one person to another during the building process. The traditional way of mixing the clay/sand/straw is with the bare feet; for this reason, it is fairly labor intensive. Some of the process can be mechanized by using a backhoe to do the mixing, but that diminishes the organic nature of it. Because of all the straw, cob can be slightly more insulating than adobe, but it still would not make a very comfortable house in a climate of extreme temperatures. The wonderful thing about cob construction is that it can be a wildly freeform, sculptural affair. I've seen some very charming homes made this way. Cob was a common building material in England in the nineteenth century, and many of those buildings are still standing.
A variant of cob is what is commonly called "light straw/clay". This is made with the same long fibers of straw which is tossed like spagetti with a sauce of clay slip. The idea is to coat the straw fibers with enough of the clay to get them to stick together, but not so much that it makes a gummy clump. This material is then tamped into a form and left to set up enough to remove the form. Light straw walls could be useful for interior partitions and even exterior walls if it is thick enough. Such walls would be quite a bit more insulating than cob, but they require a timber frame of some sort because the straw itself would not be load bearing.
Definition source:Â www.greenhomebuilding.com
Living Earth Structures - A very well done site with easy to do projects to bring life to your home or backyard!
Cob Builders Handbook - Addresses all the fundamental building questions you need answered to build acobÂ home yourself