Leichtlehm
From Swikipedia
Introduction
Leichtlehm (light foam) is a straw and clay mixture, which after being moistened and pressed between forms, hardens into a strong material. It is typically used for making walls and is an old and durable German technique.
Brief Description
The technique consists of surrounding a frame structure with a thick infill of the straw-clay mixture. The frame is usually fully expressed on the interior of the building to take advantage of the beauty of the timber frame joinery. A lighter frame of wood is built on the eventual outside face of the building as an anchoring system for the straw-clay walls.
Loose straw and clay slurry are tossed with pitchforks or mixed mechanically, then allowed to age for up to several days in order to allow the straw to absorb the extra moisture and thus create a stickier and more easily tamped mixture. For higher insulation values, less clay can be used. Slip forms are set up between the framing members and the straw clay mixture is tamped by hand in two-foot layers.
Occasional horizontal members spanning between the exterior frame are placed in order to "lock in" the straw-clay mass. Once each layer is complete, the slip form is moved up and the next layer is tamped until the wall is complete. The walls are allowed to dry before final plastering occurs. Any shrinkage is taken up by stuffing more of the mixture into the cracks.
A variant on the straw-clay technique utilizes wood chips mixed with clay; the resulting mixture is poured into removable or sacrificial forms. This technique can also be used to create lightweight bricks.
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