Cavity wall masonry
Cavity wall masonry includes an exterior wythe of brick/stone/other installed with an air gap, or cavity between the masonry veneer and the backup wall. The brick/stone is generally held in place with masonry ties, and water that infiltrates into the cavity can drain out of the assembly using through-wall flashings and weeps. This style became popular in the 1950s and is roughly the same style used in modern brick construction.
Buildings from all three categories still exist and are a part of our useful building stock. Many have brick deterioration related to masonry growth, and many have been restored including brick/mortar replacement and potentially movement provisions (i.e. movement joints). Depending on the type of damage, they may require basic maintenance, restoration, or a full assembly replacement.
Movement
The volume of a clay brick begins to change from the day it is installed on a building’s exterior. A wall of brick can expand and contract together, creating differential movement with other portions of the building, leading to stressing and then separation. The brick might be moving at a different rate than the adjacent stone masonry pieces, perpendicular to the brick on the other side of a building corner, or in the opposite direction of the structural elements supporting it. This discussion calls for a review of a few of the main sources of movement in masonry structures.
Thermal expansion
Every material used in construction experiences movement when undergoing temperature change. This movement is persistent throughout the life of the brick masonry and cycles throughout the yearly temperature changes. Brick Industry Association (BIA) Tech Note 18 recommends using a thermal expansion coefficient of 7.2 x 10-6 mm/mm/C (4 x 10-6 in./in./F). For example, a 30.5 m (100 ft) wide wall will grow 12 mm (0.5 in.) when undergoing a 37.8 C (100 F) temperature change.
