All About Cob: A Sculptural, Natural Building Material
How is Cob Made?
(images via: middle earth home)
First, cob builders must test the earth that is available to them to check the proportions of clay and sand and adjust it accordingly. Long straw fibers are mixed into the clay and sand to provide tensile strength. After adding water, cob builders mix it all up, usually by stepping on clumps of it on top of a tarp. Globs of the cob mixture can then be slapped onto a stone foundation to create walls.
There are a few variations of this technique. Some builders choose to use heavy construction equipment to mix the cob, as doing so by hand (or rather, by foot) is a labor-intensive process. The cob can also be shaped into ‘loaves’ and then arranged neatly to form the walls. The mixture can be smoothed over by hand or trowel, and uneven parts are shaved away or built upon as the walls are raised.
(images via: tiny house blog)
Pipes, wires, outlets and other necessary additions are laid into the walls as they’re built. Wooden anchors called ‘deadmen’ are also buried within the cob; these will provide the support for doors and windows. When the walls are complete, they are allowed to dry thoroughly, usually for several weeks or even months. Cracks that have formed in the cob as it dried are then repaired.
(images via: gordecosense)
Earthen plaster is used to smooth over the walls for the final finish. This is typically made using a creamy mixture of earth, water, manure, wheat paste and sometimes natural fibers like cattails. Bare cob floors can be simply finished with linseed oil for a surprisingly durable, beautiful look. For a full how-to, see ‘The Hand-Sculpted House: A Practical and Philosophical Guide to Building a Cob Cottage.’
Next Page – Examples of Beautiful Cob Structures