Cob: Sculptural Monolithic Earth

Cob is a mixture of clay, sand, and straw that is combined with water into a plastic mass and applied directly by hand in layers to build monolithic walls. Unlike adobe (which is formed into discrete bricks), cob is worked as a continuous plastic material — closer to pottery or sculpture than to bricklaying. This gives cob walls an organic, sculptural quality that is difficult to achieve with any other building material, and it allows curved walls, built-in furniture, and complex forms that would be expensive or impossible in conventional construction.

Cob walls are extremely strong in compression and have good tensile strength due to the fiber reinforcement of the straw. They are self-supporting for wall heights up to two stories without additional reinforcement. Like adobe, cob has excellent thermal mass properties and good moisture management characteristics in appropriate climates. Cob is generally best suited to mild, temperate, and semi-arid climates where moisture is manageable; in wet climates, exterior protection becomes more critical.

Building with cob is labor-intensive but requires no specialized equipment and minimal material cost. The clay soil and straw needed are typically available locally or within a short distance of almost any building site. Cob buildings can be built by unskilled volunteers with good instruction, making them well-suited to community building projects and owner-builder situations.