COB – RAMMED EARTH – CLAY LUMP – WATTLE AND DAUB – CLAY PLASTERS
Earth has been used for construction for at least 10,000 years, and 30% of the world’s population live in earth homes. Earth’s advantages as a building material are simple: it’s everywhere, it’s free and it’s incredibly durable.
A very beautiful and versatile form of earth building is cob. Cob is simply clay, sand and straw mixed into a workable mass. This mass can be sculpted into rounded forms, flowing curves and imaginative features.
In many areas of the UK, the raw ingredients for cob can be dug straight from the foundation trenches on site. This means that the bulk of your construction material is free, and its carbon cost is almost nothing.
Cob is a load-bearing material with a high compressive strength (if you’re interested: 0.77N/mm2), so a cob wall needs no additional structural support. Cob is also very durable. The oldest cob structures in the UK are 700 years old, and there is no reason why they shouldn’t last many centuries more.
The uses of cob are not limited to walling. Cob can also be used to create beautiful earthen floors. These are hard-wearing and highly water resistant. After careful compaction, oiling and waxing, a cob floor will give you a stunning, healthy surface that connects you directly to the earth. Cob is also used to make benches, ovens, fireplaces and more besides.
Other forms of earth building use varying proportions of clay, aggregates and straw, but the principle is similar. In clay lump construction, the earth is formed into blocks which are mortared together with a clay slurry; rammed earth uses a formwork and manual or pneumatic rams to shape the wall; and wattle and daub is an earth mix applied to a wooden lattice.
As an element in natural building, earth provides excellent thermal mass. Earth stores heat within itself and releases it slowly, helping to regulate the temperature of a building through heating and cooling cycles. Earth also works in tandem with breathable renders and plasters to regulate humidity levels, absorbing moisture when humidity is high and releasing moisture when humidity is low.
All this means that earthen houses have very stable temperatures and humidity levels, creating a pleasant, healthy environment which won’t suffer from dampness or temperature extremes. Many people also derive huge satisfaction from being encircled by a solid lump of earth which has not been transported or processed – just lifted from beneath their feet.