Cob

The world’s most sensual building material

Since prehistory people have used whatever materials are locally available to build their houses. You name it, people have built with it: wood, stone, grass, turf, ice and snow, concrete and steel… even tyres, bottles and drinks cans.

But perhaps the most widely used building material on Earth is… earth. Between a third and a half of the world’s people live in earth houses.

There are a wide number of different techniques for building with earth. The method we use, cob, originated in Devon (in the south-western UK) in the middle ages but was largely abandoned by the early 20th century before being rediscovered (or reinvented) both in the UK and North America.

What is cob?

Cob is a mixture of clay, sand, fibre (usually straw) and water in controlled amounts, which is used to build with while wet and dries to form an amazingly strong, durable and quite well-insulating building material. It can be used to create walls, floors, arches, shelves, buttresses, domes, sculptures… practically any shape you can imagine, you can build with cob; it’s a bit like making a house out of plasticine. Cob is extremely pleasant and healthy to work with, and encourages creativity. It’s also very flexible and recyclable: just re-wet it and re-work it into a different shape! In fact, it is the world’s most sensual building material.

You can mix cob with your feet, bare or otherwise, but we normally use a rotavator (rototiller) to save time. It also saves fossil fuels, unless the people doing the mixing are eating a local, sustainable diet.

In a damp climate like that of northern Spain, where we live, a key requirement for a durable cob house is a good roof and good foundations (“a good hat and good boots”). But unlike many people imagine, a cob house doesn’t melt in the rain — although it does help if there is also a good waterproof yet breathable layer of lime (never cement) plaster on the outside.

Earth, as a building material, is downtrodden and overlooked, yet ubiquitous, free, stable, non-toxic, sensual, and just fun to use. Some people think earth is the building material of the past; we think it’s the material of the future.