Cob, in this case, has nothing to do with the skeleton of an ear of corn. Cob is an old English term for mud buildings constructed without standard structural underpinning (Elizabeth 25). Cob is also the name of the loaves of mud used during construction.

The basic composition of cob is clay, sand, straw, and water. Cobbers typically begin with whatever soil is at hand, and amend the components to obtain the highest quality cob possible.  Below is a simple soil test that can be performed at the building site. Referred to as a “shake test,” this is a method for roughly determining how much clay and sand is available in site soil. The shake test is not a foolproof determination, but is useful in garnering site information.  Clay and/or sand may be brought in from off-site, but this begins to increase building costs.

Once a site is selected and prepared, the fun begins. New school cob is typically mixed under human power, usually by foot. Called “cob dancing,” the muddy mix is stomped out on a tarp. As the cob is combined, more elements are added—straw, water, etc.—in order to create the desired consistency and balance of elements. 

That balance can be determined by making test bricks and allowing them to dry thoroughly. Bricks deficient in sand or long straw will be in danger of cracking or breaking under pressure. The perfect mix is also determined in part by building conditions. For instance, in warm, dry conditions, a wetter cob can be mixed. In cooler, damper weather, a somewhat drier cob will prove easier to work with and will dry faster.

Regular cob is mixed on the tarp and then shaped into loaves, as this illustration from The Hand-Sculpted House demonstrates (Evans 182). These loaves, or cobs, are carried to the building in progress and incorporated.

“Gaab-Cob” is a system named for Cob Cottage Company colleague Dana Gaab. Gaab invented this wetter cob in 1994. It is loaded onto walls in large armfuls or by fork. In the photograph below, Ianto Evans of Cob Cottage Company is working with Gaab Cob.




The cob designer and architect is limited by imagination and little else. Because of this free-flowing process, cob design  might almost be thought of as a form of “anti-architecture.” In addition to the unique windows, arches, benches, shelves, and freeform sculpture possible, the house can incorporate recycling efforts in an amazing fashion. Figure 10 below shows how. The various objects that would normally end up in a landfill become an integral—if invisible—part of the finished cob structure! Because cob has such efficient thermal mass, it is ideal for passive solar construction. Heavy cob construction with thick walls can average about 70 degrees without any other source of heat or cooling.

The fine details and specifics of cob building are far beyond the scope of this project, but I hope it is clear from even a brief introduction that cob building offers a level of flexibility in design that supersedes traditional architecture. 