The reason concrete block cracks is primarily due to the fact that concrete shrinks when it dries and expands when it gets wet. If you consider the dynamics of concrete, water is added to concrete in forming the block units upon curing or hydrating, the block shrinks. When the block are placed in the wall, water is added to the mortar which transfers to the block while they are wet which causes additional expansion. Grout may also be added to the concrete block which also causes expansion. This compresses the mortar joints while they are wet. From this point the wall begins to dry and as it does it shrinks. As the block shrinks, it pulls away from the surrounding materials which are also block. As these units dry together, the cumulative shrinkage creates forces in the block which exceed its internal tensile strength capabilities. Once this happens the units crack. Control joints are placed in the block at intervals of 30 ft. or less in an effort to keep the stresses localized forcing the crack at the control joint. Atlas™ brick on the other hand begin expanding as they exit the kiln. This is the smallest the brick is during its life. Brick are comprised of clays and with moisture these clays expand. Some shrinkage occurs with cold temperatures, but the predominant direction of movement is expansion. Instead of pulling itself apart as in the case of concrete block, the brick push on surrounding brick compressing all of the mortar joints making them more water tight. Cracking generally occurs at corners where the long wall tries to push the attached adjacent wall bending the corner and forcing tension at the corner which causes a crack if reinforcing isn't placed in the brick to take the tension. Expansion joints are placed in the wall to help prevent this cracking. See FAQ: " What are expansion joints?" for more information on this subject. For this and other reasons brick walls are more water tight than concrete.