It was used to build the Great Wall of China and Spain’s medieval Alhambra Palace – and now earth is back in vogue as a building material.
Climate change has spurned a new interest in the ancient technique which sees concrete pollution swapped where possible for the earth.
For centuries, mud and clay were the available means of putting a roof over your head, but the earth’s environmental credentials are behind today’s renaissance.
“One kilo of cement produces one kilo of CO2. And a kilogram of the earth emits nothing,” said Xavier Chateau of the Navier Laboratory at France’s National Center for Scientific Research.
“If we can reduce 25 percent of the volume of cement consumed globally, it will be the same as negating the impact on the climate of all air transport,” he estimated.
Known as rammed earth construction, the practice dates back to at least the Neolithic period.
It includes compacting certain soil into a mold, of sorts, to create building blocks or build up the entire wall, layer by layer.
More than two billion people in about 150 countries live in buildings made of earth, according to a 2006 guide to earth buildings by French authors Hugo Houben and Hubert Guillaud.
Proponents say it could help reduce reliance on concrete, which accounts for about eight percent of global CO2 emissions.
Earth also has a high thermal capacity by regulating its own moisture, is fire resistant, non-toxic and fully recyclable.
But it has very downsides, not least the cost, given the need to find skilled craftsmen in ancient techniques.
Hybrid ‘earth concrete’
Faced with floods, earth-built buildings need protection, because earth also has weaknesses.
A four-storey rammed earth building crumpled in the Rhone region of southeastern France in November, when the house collapsed in the department store Isere on December 22, according to local press reports.
Often substances such as lime or straw can be added to the earth to stabilize it and increase its durability.
French building materials company Saint-Gobain is experimenting with a hybrid system of “earth concrete”, combining earth excavated from construction sites, waste from the steel industry and hemp.
But purists see it verging on heresy, in the country due to complete the 9,000-seat concert coliseum north of Paris next year using recycled excavated earth.
“It’s not the same material at all,” complains the architect Paul-Emmanuel Loiret, who manages La Fabrique outside Paris where blocks and earth bricks are made from construction ruins.
Urging a “complete and rapid decarbonisation” of construction, he complained that EU legislation “prescribes materials 10 to 20 times more durable than necessary.”
However, said Chateau: “In Africa, in Burkina Faso or Malawi, it has become a kind of artisanal savoir-faire to stabilize the raw earth with cement at the foot of the building to solve the problem of water” encroachment.
‘Great demand’
Austria has the only factory in Europe so far making low-energy prefab houses using the rammed earth method.
The site, in the western village of Schlins on the Liechtenstein border, creates foundations, floors and walls using chalk, clay, chopped straw, lime or gravel.
A machine pumps the compacted earth into a large casing to produce a 40-meter (130-foot) long wall.
After drying and cutting to size, the blocks are sent for assembly.
“Given ecological challenges and energy problems, there is a huge demand for this material,” said environmentalist, entrepreneur and former potter Martin Rauch, who built the factory.
Architect Sami Akkach who worked with Rauch said he used earth from the surrounding area, buildings and excavation sites.
“You have to contain clay, gravel, angles instead of circles so that they stick,” Akkach said.
Rauch has several earth-built buildings to his name, including his house whose exterior walls are composed of terracotta designed to brake rain and erosion, a throwback to ancient methods used in Saudi Arabia.
He said the factory has the longest earthen wall in Europe – at 67 meters – and he believes the demand is there for more projects using rammed earth.
“The problem is that there are not enough craftsmen and people are still very afraid of this natural material,” he said.
He added that he hoped people would understand that “the structure of the earth will last for centuries, if it is built properly.”