B.S. EN 771-1 sets the tolerance levels for a T2 brick at +/- 4mm from the work size of 215mm, which recognises that a brick is not a precision article. This is not meant to suggest that examples at either end of this scale are to be expected within the same consignment, but recognises that brick size is dictated by the action of heat on the clays used and any variation in material content or kiln temperature can have an effect on the size of the finished product. In reality the majority of bricks tend to be within a couple of millimetres of the work size, either on the plus or the minus side. Within any batch a very small proportion (less than five per cent) may be slightly outside this.
Such variations can be coped with by slightly adjusting the joint width to suit. It is far more important to have evenly spaced joints by working within the designated workspace of 225mm (215mm plus 10mm joint) than insisting on keeping to an often unattainable 10mm joint throughout.