the prices quoted are sometimes more than
those for ordinary fired bricks. With simpler
production processes and open-air drying,
on the other hand, it was possible in at least
one German case, to obtain green bricks
that are 40 % cheaper than the price of reg-
ular fired bricks.
Material composition
The loam used in common brick plants
requires high clay content in order to
achieve sufficient strength after firing. Illus-
tration 6.21shows a typical soil grain size
distribution of this type of loam, containing
24% clay, 50% silt, 23% sand and 3% grav-
el. When loam of this composition is used
for earth block work, it creates swelling and
shrinking problems upon wetting and dry-
ing respectively. Illustration 6 .19shows
cracks occurring when these green bricks
were used in a project where a wall was
drenched by sudden rain during construc-
tion.
The soil grain size distribution of a leaner
sandy loam appropriate for earth blocks is
shown in 6.22. It shows 14% clay, 22% silt,
62% sand and 2% gravel, and shows no
Reduction of shrinkage cracks
Generally, it can be stated that earth blocks
should have enough coarse sand to allow
them to achieve high porosity (and there-
fore high frost resistance), and high com-
pressive strength with minimum shrinkage.
But at the same time, there must be enough
clay to create sufficient binding force for the
block to be handled.
Laying earth blocks
It is important to shelter earth blocks from
rain on site. In industrialised countries, as a
rule, green bricks ordered from factories, are
palletised and covered entirely in plastic.
Earth blocks are laid with either loam mor-
tar, hydraulic lime mortar or high-hydraulic
lime mortar. While small quantities of
cement may be added to these mortars,
pure cement mortar is not advisable, as it is
too rigid and brittle. To avoid shrinkage
cracks inside the mortar during drying, the
mortar should contain sufficient quantities
of coarse sand. The clay content may vary
from 4% to 10%. The formation of shrink-
age cracks can also be avoided when the
mortar layer is thinner than usual. It is a
pleasure to work with loam mortar, since it
is not abrasive to the skin. Lime mortar,
however, attacks the skin and may also
cause allergies.
65 Working with earthen blocks
6 .16
6 .17
6 .19
6.20
6 .18
