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    The most ancient of all worked materials.  Mud walls, dried in the sun and protected from excessive wet, can last for centuries and, once fired, earth can survive for thousands of years to provide buildings and artefacts of extraordinary beauty and diversity.  Earth is an abundant material easily dug at little or no cost.  It has excellent thermal-storage qualities.  A properly built earth house is durable as well as fire, rot, and termite proof.  It has an indoor climate that regulates air moisture and sound and helps to absorb and expel polluted air. 
    In construction, it uses only about 3% of the energy expended in similar concrete building.  The best soil for bricks contains 75% sand and a minimum of 10% clay.  For rammed earth, less sand and more clay and silt is preferred.  Well-compacted soil usually requires no stabilizers, but poor soils will - cement and bitumen for sandy soils and lime for clay soils.  The process is labour intensive; however, it must be noted that labour is ecologically neutral and does not harm the environment where machines and other processes add to a building’s embodied cost.

 rammed earth home by Terra Firma of British Columbia
[click image for more detailed information]

    Damp earth is placed into typical wooden forms and tamped to total compaction creating an engineered earthquake-safe wall that is similar to concrete's durability.  "Lifts" of 15cm to 20cm (6"-8") are placed and then the soil is rammed.  The process creates a stratified effect.  The look can be thought of as primal or the idea of new construction within existing ruins.  Variations in strata colour can be created by mixing different sands, gravels, etc. together.
    These walls can be reinforced with steel and embedded with a core of insulation.  The walls vary in thickness, according to their heights and loadings, from 30cm to 80cm (12" to 32") with a 10cm (4") insulation cavity.  Conceptually they are similar to unreinforced load-bearing masonry cavity walls.
    The earth walls can absorb solar radiation by day and release the heat by night.  In the summer the thermal mass can absorb excess heat during the day keeping the inside cool.  An earth house can be built in wet, temperate regions if it is built up on a well-drained damp-proof foundation with a wide roof overhang and they can be built in very cold regions if adequately insulated.
    The walls by nature can have inconsistencies in colour and texture as well as shrinkage cracks, honeycombing, and voids.  Efflourescence can occur when the walls are constructed during wet, cold weather, free lime in the soil can migrate to the wall surfaces, causing a powdery white stain to appear.
    Rammed earth is porous and in areas where snow or wind driven rain can be severe, moisture may migrate to the inside surface of the walls during prolonged storms.  In this case the exterior walls could be sealed and it is very important to provide adequate roof overhangs.  The walls must be protected from moisture during freeze-thaw cycles.  Unprotected walls will spall during successive freeze-thawing.
    As with exposed concrete, interior earth walls may cause dust.  This partially depends on the soils used.  If dust is a problem, a clear sealer can be used with the benefit that it is also easier to keep the walls clean.

Article published in On Site review, V.10, 2003, (Balancing the Humours), The Association for Non-Profit Architectural Fieldwork, Calgary.

L'Oeil Régional - Édition du 25 septembre 2004, (Pointe Valaine - Des briques fabriquées avant même le bâtiment!)