Adequacy of Compressive Strength

Mortars that are overly strong will respond to differential movement with cracks, which may be few in number but they will be large, and usually through the bricks or blocks themselves rather than in the mortar joints. Weaker mortars on the other hand are capable of accommodating small amounts of structural movement and any cracking will be hairline in nature and concentrated in the joints. In the event that remedial work is required, raking out and re-pointing joints is a much easier and quicker task than the wholesale chopping-out and replacing of cracked bricks.