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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!)
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