Lime blowing in bricks is caused by lime contamination within the clay before the bricks are fired in the kiln. Once the bricks are fired any lime deposits within the clay convert to calcium oxide also known as quicklime, which begins to slake when moisture is introduced to the bricks. The slaking process expands the material and can rupture the face of the brick as shown to the right.
Even though brick manufacturers aim to pre-emptively mitigate this issue through stringent quality control procedures, this phenomenon can occur in any brick and with varying degrees of severity. However, remedial action can be taken after the damage has been caused whereby the offending quicklime can be drilled out of the clay and then filled & refaced by specialist brick tinting / fabrication contractors in situ.