Assessing brick production
Practical Action
BRICK PROBLEM
3. STRENGTH/SOUNDNESS
(a) Weak and crumbly (all
types)
PROBABLE REASON
(i) Underfired - detectable by
dull 'clunk' not sharp ring
when bricks are knocked
together
POSSIBLE SOLUTION
(i) Use more fuel, or change
fuel distribution, or modify
kiln design
(b) Cracking (all types)
(i) Straight cracks at right
angles from one long face
(i) Drying too fast
Dry more slowly or add sand to
mix to decease shrinkage
(ii) Random surface cracks
Differential drying shrinkage
caused by presence of lumps
of drier material or stones
Mix better and/or sieve out
stones
(iii) Buling cracks or blisters
(i) Surface heated too quickly
- vitrifies before gases escape
(ii) Presence of lime in soil
causes blister - even 'popping'
(can appear after manufacture
- lime blowing)
(i) Slower firing - especially
around firing tunnels or near
fuel
(ii) Sieve out lime or crush
and mix better (powdered lime
can act as a flux and reduces
the energy/fuel needed)
4. APPEARANCE
(a) Contaminated or distorted
surface (all types)
Drying floor not clean or
smooth
Ensure floor is clean & smooth
(b) 'Spalling' - part of surface
'blown away' (all types but
particularly extruded)
(c) Drag marks (extruded &
slop moulded)
(d) Efflorescence - crystalline
deposit on surface (all types -
appears after manufacture)
Heating too fast in kiln,
residual water turns to steam
& explodes
Cutting wires contaminated
with leaves or dry lumps of
clay
Soluble salts in clay or water
Slow down initial kiln firing
process (up to 100°C)
Make sure wires are clean &/or
lubricated with water
Salts tend to be near surface,
so discard top most soil
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