www.earthbagbuilding.com
by Kelly Hart
The idea of making walls by stacking bags of sand or earth has been around for at least a century. Originally sand bags were used for flood control and military bunkers because they are easy to transport to where they need to be used, fast to assemble, inexpensive, and effective at their task of warding off both water and bullets.
At first natural materials such as burlap were used to manufacture the bags; more recently woven polypropylene has become the preferred material because of its superior strength. The burlap will actually last a bit longer if subjected to sunlight, but it will eventually rot if left damp, whereas polypropylene is unaffected by moisture.
Because of this history of military and flood control, the use of sandbags has generally been associated with the construction of temporary structures or barriers. Using sandbags to actually build houses or permanent structures has been a relatively recent innovation.
In 1976 the Research Laboratory for Experimental Building at Kassel Polytechnic College in Germany began to investigate the question of how natural building materials like sand and gravel could be used for building houses without the necessity of using binders. The use of fabric-packed bulk material was found to be a cost-efficient approach. They used pumice to pack in the bags, because it weighs less and has better thermal insulating properties than ordinary sand and gravel. Their first successful experiments were with corbelled dome shapes ( an inverted catenary) which was obtained with the aid of a rotating vertical template mounted at the center of the structure.
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