ADDITIVES TO CLAY
DERIVED FROM NATURAL SOURCES
Earth has been used for building
for thousands of years throughout
the world spanning a diverse range
of climates and cultures. Earth
itself is a multi-component system
usually consisting of stones, sand,
silt, clay, water and, near the
ground surface, organic humus.
Structural stability of earth
buildings is maintained by the
structural integrity of the sand and
stone framework, by the pore
filling capacity of the silt and,
most importantly, by the binding
qualities of the clay, which are in
Figure 1 Surface stabilisation of soil with palm oil,
Nigeria. Photo credit: CRATerre/EAG
turn influenced by the moisture
content of the soil.
Compared with some building materials earth can be considered to have some disadvantages
– it has relatively low compressive strength, tensile strength and abrasion resistance. It may
also lose a lot of its rigidity in the presence of water. Nevertheless it is very cheap, very
widely available, environmentally friendly, strongly linked to local cultures and traditions and,
with skilful construction, can contribute significantly to the aesthetic appeal and user comfort
Good and durable earth buildings can be built provided certain precautions are taken. These
precautions will depend on local conditions and structural requirements, but can broadly be
classified into four categories:
Different soils can have very different characteristics. The quality of a soil for building is
strongly dependant on grain size distribution and excluding humus.
Soil preparation and construction methods
Builders should be familiar with soil pulverising, proportioning, mixing, maturing and curing
as well as masonry techniques.
The design should take account of the properties of the raw material by appropriate load
distribution and structural dimensions, and by incorporating protective elements against
damp, rain, impact and abrasion. Protection can be achieved by adding more durable but
complimentary materials at places such as the wall base, roof overhang and the copings, and
by using plasters and renders.
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