ADDITIVES TO CLAY
MINERALS AND SYNTHETIC ADDITIVES
Introduction
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
turn influenced by the moisture
Figure 1: House with stabilised soil render in Atlas
Mountains, Morocco. Photo: CRATerre/EAG
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
of buildings.
Good quality 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:
Soil Selection
Different soils can have very different characteristics. The quality of a soil for building is
strongly dependent on grain size distribution and the exclusion of humus.
Soil Preparation and Construction Methods
Builders should be familiar with soil pulverising, proportioning, mixing, maturing and curing
as well as masonry techniques.
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