Mortar and Movement
When describing the differing performance of mortars, it is generally acknowledged that weaker ones are more tolerant to movement than stronger ones. This should not be taken to mean that they are flexible in the pliable sense. They respond to movement stresses by generating general minor fractures within the jointing rather than concentrated major cracks through the bricks and mortar. This concept has been already noted in relation to calcium silicate bricks and shrinkage and to the use of mortar 'no stronger than bricks'. Although lime is thought to give mortar 'healing' properties that re-bond minor cracks, no modifiers or additives in use today create a pliable mortar.