All building materials change in volume due to internal or external movement.  When these movements are restrained, cracking often occurs that can lead to water infiltration, efflorescence, unit failure, interior deterioration, or mold generation.  To avoid cracks in masonry walls, movement joints must be incorporated into the building design. 

Clay Masonry

In clay masonry walls, vertical or horizontal expansion joints, or both, may be required depending on the dimensions of the wall.  These joints create a continuous unobstructed opening through the full depth of the brick wall.  When properly installed, expansion joints prevent the anticipated expansion that results from wetting or temperature changes, and can also provide relief from movements due to elastic deformation from loads and creep.  Care must be exercised to assure that mortar or other non-compressible materials do not protrude into the expansion joint to nullify its function.

Concrete Masonry

Control joints are used in concrete masonry.  A control joint creates a weakened plane to restrict volume changes that can result from shrinkage and creep.  Like expansion joints, control joints must also provide a through-wall separation, but are usually designed to include a shear key to transfer lateral loads across the joint.  Joint reinforcement must be terminated at control joints to permit unrestrained movement of adjoining wall segments.