Perhaps, when you first heard the terms "cob structure" and "cob building," you thought it had something to do with constructing buildings from corn cobs. Actually, cob building is a form of earth and straw construction that is quite ancient.
Cob building is a variation on the mud brick idea. Indigenous earth is mixed by hand (or more traditionally, by using the feet) into a mud, then long straw is added. The proportion of straw to mud is greater than that used for baked bricks. The gloppy mixture is then piled and sculpted into dwellings.
Handfuls of the cob mixture can be tossed from worker to worker, eliminating the need for machinery such as cranes. It is a very durable kind of construction; centuries-old cob houses are still standing in parts of the British Isles.
Because earth is available everywhere, some variation of cob housing has occurred in many parts of the world throughout history. A variation of this is a kind of cob structure where the mud used is quite thin, and just enough of this thin mud is used to stick long straw strands together. This mostly-straw mixture is tamped into a mold or frame, and when it hardens, the frame is removed. Such "light straw/clay" buildings are more insulating that traditional cob, but not as structurally sound. Walls that are mostly straw, even with mud mixed in, cannot bear much weight.
Traditional cob buildings are not suitable for areas of the world where there are temperature extremes. For temperate climates, however, cob structures can provide strong, dry, durable dwellings that lend themselves to creative shapes. Therein lies cob's charm: artistic builders can create sculptural buildings in creative, organic shapes. There are few limitations to the design of a cob structure.
Cob dwellings are labor-intensive, and they take quite a bit of time to build. The walls need to "cure," a process that can take up to a year. And not everyone likes a curvy, sculptural home.
Cob houses are eco-friendly. Their mud and straw construction does not use any non-renewable resources, nor does the building process require any fossil fuels (no machinery is necessary). It is also extremely economical; cob houses can be built for less than $1000.
A great deal of professional skill is not required. The internet, libraries and bookstores carry all kinds of how-to information on cob buildings. It is definitely a building technique that is making a comeback.
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