Assessing brick production
Practical Action
Laboratory tests
If bricks have to satisfy an official
standard, they will probably have
to be tested in a laboratory. These
tests will need to be repeated
periodically to maintain quality
control. Tests normally specify the
sizes for bricks and the acceptable
compressive strength - how much
weight they can bear before
crushing2. For example, in
Zimbabwe 'common' bricks are
nominally 220 x 105 x 75 mm
and have a crushing strength of 7
MPa. For certain uses, such as
damp-proof courses, water
absorption or suction rate may also
be specified.
Figure 3: Coal fired bricks drying in sun Zimbabwe.
Photo: Practical Action / Theo Schilderman.
Raw material tests
The quality of brick which can be made at a particular site is largely predetermined by the type
of soil available. There are some simple soil tests which don't need very special equipment. In
the sedimentation jar test, a sample of soil is dissolved in a jar of water. When the soil settles
you can get an idea of the fractions of clay, fine and coarse sand that are present. Another test
is the linear shrinkage test. A sample column of wetted and mixed soil is pressed into a mould
and allowed to dry. The shrinkage indicates how much clay there is in the soil and whether
problems can be expected when drying bricks3. Soil test are useful indicators, but you really
only find out whether good bricks can be made by firing samples. Before investing in a full
size kiln, however, it is possible to fire cubes or eggs of soil either in a laboratory kiln or a
simple field oven.
Conclusion
These guidelines will help field-workers judge the quality of bricks. Furthermore, if the
information presented is used as a basis by those working with brickmakers, it will go some
way to establishing an agreed approach to assessing the technical problems they face and
proposing appropriate solutions That is, solutions which make the best use of available
resources: are affordable, manageable, cost effective, and - ultimately - 'successful'4.
Reference and further reading
Ten Rules for Energy Efficient, Cost Effective Brick Firing: A Guide for Brickmakers
and Field-workers Practical Action Technical Brief
How to Measure the Energy Used to Fire Clay Bricks: A Practical Guide for
Brickmakers, Field-workers and Researchers Practical Action Technical Brief
Sustainable Small Scale Brick Production: A question of energy, Practical Action
Technical Brief
Drying of Clay Bricks and Tiles GTZ Technical Brief, Gerhard Merschmeyer, 1999,
Moulding of Clay GTZ Technical Brief, Gerhard Merschmeyer, 2001,
Brick Clamps GTZ Technical Brief, Tim Jones, 1995,
Bull’s Trench Brick Kiln GTZ Technical Brief, Henrik Norske, 1995,
Hoffmann Kilns GTZ Technical Brief, Tim Jones, 1995,
The Vertical Shaft Brick Kiln GTZ Technical Brief, Tim Jones, 1997,
Firing of Clay Bricks & Tiles, GTZ Technical Brief, Gerhard Merschmeyer, 2000,
Preparation of clay for Brickmaking, Gerhard Merschmeyer, 1999,
Village Level Brickmaking, Anne Beamish & Will Donovan, GTZ / Friedr. Vieweg &
Sohn, Braunschweig, Wiesbaden, 1989,
The Clay Industry: Improvement of Resource Efficiency and Environmental
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