Ever heard the expression, “dirt cheap?” Of course you have, because dirt is cheap. It’s everywhere. No matter where you go, there it is. The folks at Architecture & Design say, as a building material, rammed earth is cheap, tough, and green. So why is not used more often in construction?
If you think nothing made of dirt can possibly be durable, consider this. Both the Great Wall of China and the iconic Alhambra palace in Spain are made of rammed earth and have been around for more than 1,000 years. Rammed earth is a mix of clay-rich soil, water and a natural stabilizer such as animal urine, animal blood, plant fibers or bitumen. It is compacted inside temporary forms until it hardens. The resulting structure can withstand pressures up to 400 psi. That’s about 10% of the pressure modern bricks can tolerate.
Rammed earth walls can be reinforced with timbers or latticework made of bamboo. It has been used for centuries for buildings in South America, China, India, the Middle East and North Africa.
In the past 30 years, a new kind of rammed earth has emerged that substitutes cement for urine, blood or plant fibers. Called cement stabilized rammed earth (CSRE), it is a mix of low clay soil, water and cement. When the mixture dries, it has the same rating as concrete – about 6000 psi. CSRE has been used in Australia, California and Canada.
The first advantage of rammed earth is low cost. Dirt is available everywhere and is usually inexpensive if not free. Since it is available locally, the cost of transporting building materials is eliminated.
Usually, only one trained worker is required. The majority of the form building and mixing can be done by unskilled local workers. Once again, that keeps costs low. The finished walls have a unique beauty of their own and require no exterior or interior finishing.
Traditional and modern rammed earth structures are being built in many countries around the world to provide inexpensive shelter of indigenous people. The government of Western Australia is considering this approach and in the US, Colorado University wants to use rammed earth for homes for Native American families. China’s Xi’an University of Architecture and Technology is helping rural communities build entire new villages using rammed earth.
Why Aren’t Others Building With Rammed Earth?
Since rammed earth is cheap, tough and green, why aren’t more people using it to build with? The answer is twofold.
First, even though it is an ancient technique, few people today have ever heard of it. That lack of knowledge is changing, though, as word of the advantages offered by building with rammed earth gets out. Second, local building codes usually have no standards for rammed earth construction. The idea of working with an unregulated construction technique discourages many engineers and architects.
The good news is that the interest in environmentally friendly and affordable houses has never been higher. Experts in engineering, materials science, architecture, and chemistry are beginning to consider rammed earth for future building projects. In architecture as in many other areas of human endeavor, everything old is new again.