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An article called Terra Firma in the June 2, 1996 San Francisco Examiner describes using earth combined with concrete to produce energy efficient and rammed earth homes. After the cataclysms, building materials such as wood or stone may be in short supply, and using earth to extend the available concrete may be just the thing. The article states, in part:

For all of recorded history, dirt has been the primary source of building material. As many members of our species grew up in caves, it was natural that humans would fashion earth into walls, as they did in the Kasbah of Morocco, in the Great Wall of China, in the Alhambra in Spain and in the ancient Anasazi pueblos in what would become the American Southwest. Earthen walls - poured and compacted into wooded forms - can last a millennium. In some rural regions of France, 90 percent of buildings are made of earth.

Now, thanks to the tireless efforts of a Stanford University engineering graduate, the construction industry finally seems to be catching on to "rammed-earth" construction, as it's called. ... Easton's firm, Rammed Earth Works, currently is working on earth homes. ... He has written a just-published book, "The Rammed Earth House," that is generating increased interest in the technology.

Rammed-earth walls are built 18 to 24 inches wide - that's two to more than three times as thick as conventional framed walls - which keeps the building cool in the summer and warm in winter. ... Rammed-earth homes are built by erecting plywood forms, then layering clean, moist soil mixed with a small amount of cement into the form and ramming it until it's hard and only about 50 percent of its original volume. The material is packed with pneumatic or hand rammers and the forms can be removed almost immediately.

When finished, the rammed-earth wall is essentially reconstituted sedimentary rock. Its strength rivals concrete. ... Whereas concrete typically has four to six sacks of cement pre cubic yard, rammed earth uses only one or two. The bulk is made up of clay. The resulting walls are fire-proof, rot proof, termite proof and nearly soundproof.