Q: I have noticed many vertical cracks in the brick veneer on a recently completed 20-story high-rise condominium building. The building has a concrete structure and exposed concrete balcony slabs. The cracks are occurring where the brick veneer wall returns at recessed balconies. In most cases, the cracks are vertical, but occasionally they are stepped. It appears as if the veneer on the face of the wall is moving up and the brick at the return is binding on the underside of the projecting slab above. However, there are expansion joints at each floor line that should prevent this. What could be happening?
A: Although there are expansion joints at every floor line, they may not be functioning properly. This can happen for many reasons. Mortar from the head joints of the brick veneer below may have squeezed out during original construction and be in contact with the underside of the angle. Mortar or other debris may have filled the joints in other ways. When mortar or debris blocks the open space beneath the angle, differential movement between the veneer and the structure is not accommodated.
It is also possible that the gap beneath the angle may have been constructed too small to accommodate the amount of differential movement that occurred. In this case, masonry thermal or moisture expansion, coupled with concrete frame shortening, may have closed the gap. Once the gap is closed, any additional differential movement between the brick veneer and the concrete frame would cause the brick veneer to press up against the underside of the angle.
Most concrete frame buildings use wedge inserts embedded in the spandrel beams to anchor the shelf angles to the building structure. When this is the case, vertical growth can lift the relieving angles.
The brick veneer on the returns at the balconies will resist this vertical expansion, resulting in vertical or stepped cracking between the brick veneer on the face of the wall and the veneer, as shown in Figure 1. These problems often first appear in upper floors, where the accumulated differential growth can be the greatest. The brick veneer on the returns at the recessed balconies could have been constructed tight to the underside of the projecting concrete balcony structure. In this case, the cracking could be resulting from concrete floor deflections in addition to vertical brick veneer expansion.
If there are no vertical expansion joints (or if the expansion joints are closed or blocked) and the length of brick veneer between the balconies is 25 feet or more, the cracking may be the result of horizontal growth of the veneer. As the brick veneer grows laterally from moisture and thermal expansion, it will push against the veneer return at the recessed balconies. Since this brick veneer is restrained by wall anchors and connections at window or door openings, the veneer will crack at the corners, as shown in Figure 2.
Resolving this problem requires investigation. Examine the horizontal expansion joints beneath the relieving angles, as well as the joint between the underside of the balcony and the top of the brick veneer return. Also review the placement and condition of any vertical expansion joints.
When repairing horizontal expansion joints, it is important to begin work at the top of the building. If vertical growth has lifted the brick veneer, you will need to make openings to tighten the bolts in wedge inserts since these are loosened by vertical movement. Otherwise, the brick veneer will shift downward during repairs. When installing vertical expansion joints at balcony corners, the joints must extend the full height of the brick veneer. This may require removing some brick units at the top and bottom to form the joints.