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Mud Bricks

Mud brick (also known as adobe; from the Spanish word for earth) is one of the world's oldest building materials. It is used in buildings dating back centuries and even thousands of years. These include the Great Wall of China, the Bam citadel in Iran, giant temple complexes in Peru, the Grand Mosque in Timbuktu, the world's oldest skyscrapers in Yemen and the beautiful Native American architecture of Santa Fe, New Mexico.

Mud bricks are simple to make, attractive and durable. They are also environmentally friendly, needing no energy to manufacture. And after all, if you want to build an earth-friendly home, why not build it from earth itself?

Mud bricks are made by mixing earth (clay and sand, but not topsoil) with water. Straw or other fibres can be added to help reduce cracking. The mixture is placed into moulds to begin drying, then the bricks are removed to finish drying in the open air. Mud bricks are usually bigger than a conventional brick, weighing up to 18kg, although they can be made to any size.

Mud brick walls are normally single skinned. They can be load-bearing but in Australia it is more normal to build mud brick homes with a timber or steel frame construction. The bricks are joined with a mud mortar made from the same earth-water mix as the bricks, the only difference being that it is not dried.

Footings are usually strip or concrete. A concrete slab also provides a clean, flat surface for making the mud bricks. A damp proof course is laid between the footings and brick wall to prevent rising damp, while a splash course of fired bricks will prevent erosion of the lower course of mud bricks from heavy rain.

Making your own mud bricks

Mud bricks are very simple to make, and can easily be made by non-expert owner-builders. This offers significant savings, as bricks and bricklaying can make up about 20 per cent of a home’s total cost. However, although technically simple, the process is time-consuming and physically hard work. It could take an owner-builder couple working in their spare time up to a year to make enough bricks for a house. If you don’t want to make your own mud bricks, there are suppliers who make the bricks and deliver them to your site.

Finishes

Mud brick walls can be finished to provide different effects. For a smooth finish, you can fill in the mortar level with the bricks, or render the wall by smoothing an additional layer of mud over the surface. Alternatively you can scrape out the mortar so the bricks stand out to emphasis the natural, organic look of mud bricks.

Mud bricks give an attractive, earthly look if left unpainted. Their exact colour will depend on the colour of the clay and sand in the earth. Alternatively you can paint the walls after they have been rendered. You can buy paints specially formulated for mud brick walls, or make your own mud paint by mixing clay with water.

Walls can be finished with a sealant, such as linseed oil or turpentine, to prevent water penetrating on the outside and to make them easier to wipe clean on the inside. Large overhangs or eaves on roofs will provide additional protection from harsh weather such as driving rain.

Insulation and thermal mass

A mud brick wall performs similarly to a brick veneer wall in terms of heat insulation. It does, however, have better noise insulation qualities and higher thermal mass. (This is because mud bricks are solid and dense. Their density blocks noise and absorbs heat. Effective heat insulation, on the other hand, is largely provided by pockets of air in a material, which trap heat and stop it moving through the material.)

Why is mud brick environmentally friendly?

• The earth for making the bricks can often be taken from the property itself, which eliminates the energy use and greenhouse emissions from transporting the bricks.

• Mud brick can have very low embodied energy: no energy is needed to make the bricks, except human labour and the sun's heat. (It takes a lot more energy to fire conventional bricks.)

• At the end of the building's life, mud bricks can simply be broken up and turned back into earth.

• Mud brick provides good thermal mass, which can be used for effective passive solar design to store heat during the day for slow release at night - good for climates with warm days and cooler nights.