The amount of cracking in brick can be controlled by using control joints and appropriate reinforcement in the footing of a building. The foundation may be atop poorly compacted soil or next to deep trenches causing settling of the footing. Properly testing the soil will help determine the probability of settling and aid the engineer in designing footings that may avert problems. Another difficulty may arise when you do an add-on because it is difficult to tie into the old footing for a smooth transition.
Stress may be caused by changes in temperature, moisture content or chemical reactions in the masonry. Cracks in the brick may occur vertically and spread through mortar joints or they may appear as though they are “stepped,” or stretch upward from the top of windows or doors. They may be cyclic, active or passive. An active crack will continue to increase in size whereas a passive crack remains dormant. Cyclical cracks fluctuate with the season. Passive and cyclical cracks are harmless, but active cracks require the expertise of a structural engineer.
Concrete and silica bricks shrink because they lose moisture while clay bricks swell as they collect moisture. Proper installation of expansion joints prevents the movement caused by the shrinking of the mortar between the bricks. The type of brick you use may determine the spacing and therefore the problems associated with expansion joints, such as correctly designing for shrinkage or expansion and controlling the stresses caused by movement of the foundation.
Buildings may sit atop a poorly designed structural support. That, along with inadequate jointing, improper mortar mix or removing props before bricks are set, may create situations where bricks may crack. Other symptoms of inadequate structural support may be vertical cracks near supporting beams, wider cracks at lower ends, diagonal cracks and an increase in the width of the cracks over time.