The percentage of the cement paste that goes into each mould filled with concrete, along with other factors such as particle size distribution of the aggregates used and method of packing will be the determining factors for obtaining a uniform compressive strength for all the cube samples...
There are good chances that the masonry wall might have cracked due to differential settlement of the foundation beneath it.
There is also a chance that the cement used for masonry may contain a high content of free lime or magnesia, which inturn may cause cracks in the wall.
The solid cement...
