I have cracking problems in a masonry building with a masonry parapet. The walls are brick veneer cavity walls with concrete-block backup. The parapet has brick veneer on the outside face and on the parapet face. The space between the two brick wythes was reinforced and grouted solid to attach the parapet to the building structure. Cracking has developed between the brick veneer cavity wall and the solid-grouted portion. Why is this cracking occurring and what can I do to correct it?
The cracking likely is occurring because the masonry veneer at the cavity wall and the solid-grouted masonry are trying to move in different directions or at different rates. The grouted masonry parapet walls are restrained from growing by the grout core and reinforcing steel. The masonry below the grouted parapet is restrained only by the mortar joint between the grouted parapet and the cavity wall. Shear stresses that develop as a result of this differential movement can easily exceed the shear strength of the mortar joint. If this crack does not cause structural problems, I recommend grinding the joints to a depth of 3_4 inch and applying backer rod and sealant. This detail will permit the masonry above and below this joint to move independently.