For a brick to be irregular, one of the following imperfection (types of brick irregularity) is
present: variation in size (due to variable shrinkage), warping or curvature, taper and surface
roughness. These are considered in turn in the following sections, where the causes,
consequences and avoidance of each are discussed.
5.1.1 VARIABLE SIZE
These are variations in the size of bricks within or between mix/batches, which cause the
a) Causes of variable shrinkage
Brick shrinkage occurs because of moisture evaporation during the drying process. However
this is of small impact unless the soil used contains a high fraction of clay that is prone to
excess shrinkage. If there were constant shrinkage within or between the batches there
wouldn’t be any problem. Non-uniform shrinkage may be caused by one or more of the
following: -
• Excess water in the mix,
• Poor mixing,
• Changes in soil properties,
• Differential compacting pressure caused by poor batching (uneven amount of mix
placed in a mould for each compacting cycle)
• Poor curing (described in more detail in section 5.2)
b) Implication of variable shrinkage on wall alignment
The poor matching (in height, length are easily visible) of bricks during wall assembly delay
construction and cause additional activities (selection, shaving, shimming and replacement of
rejects) that increase construction cost.
c) Remedial measures to control shrinkage
To minimize the outcome of excess shrinkage will require systematic monitoring and close
supervision of all processes to brick production, which include: -
• Treating soil with the correct type and amount of stabilizer (proper designed ratio of
cement to soil)
• Mixing with proper water/moisture content (proper water/cement ratio)
o Pulverizing to remove hard particles
o Sieving to a required size/limits
o Mixing to a standard consistency (by sight)
• Use of adequate compacting pressure during moulding
• Proper curing conditions: -
o Under a roof and on a level floor or
o In the open air with proper flooring and covering materials (plastic sheets,
grass, sawdust etc.)
However the occurrences of variations in brick size due to shrinkage are in general practice
minimised and not eliminated. The remedial measures taken are to prepare and correct them
to be fit for use, as described in Section 5.2.
5.1.2 WARP (CURVED OR TWISTED BRICKS)
These are the changes in brick shape not in right form (twisted), which at the same time may
change the size of the brick.
a) Causes of warped, curved or twisted bricks
In soil stabilization, warping and twisting may occur mainly due to two causes (both
considered in 5.2 below): -
One is rapid drying of bricks cured at the open air without cover. This practice has been
inherited from the production of mud bricks, which normally are left in the open air to dry.
countries. For these two reasons bricks are often of poor quality having irregular shapes
(warped, curved and with severe shrinkage).
b) Implications of warped, curved or twisted bricks for wall alignment
The implications of warped and curved bricks to the wall alignment are more severe than
shrinkage alone, because shrinkage is a linear change to all sides, so to deal with it is simpler,
but warping forms surfaces with ditches and humps. Warped and curved bricks when dry-
stacked make contact at specific points (bumps). If these points are scattered over the surface,
during assembly the contact of the two brick faces will induce rocking, rolling and pitching
until a stable position is found. Moreover placing another brick above may change the lower
brick’s balanced position. This may result in the phenomenon of ‘lateral softness’ that causes
difficulties in maintaining good vertical wall alignment. To stabilise, the structure will require
strengthening i.e. shimming, addition of buttresses etc.
Due to having low contact surface areas between them, bricks develop load concentrations at
their contact points. This concentrated loading easily surpasses the crushing strength of bricks
and therefore resulting in cracking or failure of individual bricks. To prevent cracking in the
case of severe warping, bricks may require a lot of shimming as in traditional bricklaying,
which of course mortarless technology is trying to avoid.
c) Remedial measures to reduce warping, curving and twisting of bricks
Warping, curving and twisting for stabilised bricks can be reduced by proper curing i.e. under
a roof and or under the covering of plastic sheets, grass or any other material to reduce
exposure to air and sun and thus prevent quick evaporation of moisture. The other remedial
measure is making curing-floor surfaces level and hard to reduce moisture percolation into
of brick irregularities; so curing require proper control and close monitoring for effective
performance. Warping and curving can be much minimised on fulfilling the above-
recommended remedial measures. But shrinkage, which is associated with the soil properties,
will remain a task to be addressed by proper soil selection and proper design of the ratios of
cement to soil and water to cement.
5.1.3 BRICK SURFACE ROUGHNESS
The rough-surfaces (random localised bumpiness) of the brick’s faces designed to form
contact, normally are the top and bottom faces that the mortarless technology should direct
more attention. The causes and consequences don’t differ much with those described in
Section 5.1.2, so, do the remedial measures. The emphasize should be on the quality of curing
places and the stacking practice, to keep floor always clean, flat and smooth will protect brick
faces from roughness.
5.1.4 TAPER
These are uneven brick shape changes due to general wear and tear of the press, changes in
mould box dimensions due to bulging or twisting to one side and rocking of movable plate of
press. We leave aside intentional vertical taper introduced to make demoulding easier,
although with wear this may grow to exceed the allowable tolerances. Close monitoring and
control of any source of taper (i.e. having non-parallel top and bottom faces) will give a
warning of brick biases forming. Consistent bias can be corrected by reversing alternate