Concrete masonry construction was common practice in post-war Modern architecture where it was used extensively in schools, churches, public buildings, and industrial complexes. Brick and concrete block-bonded construction gained favor in many public buildings for its perceived durability, aesthetics, and relative ease of construction. Over 50 years later, many of these buildings now have historic significance but suffer greatly from neglect, environmental hazards, and reduced service life. The feasibility of restoring and preserving these buildings demands better understanding of problems inherent to their construction and premature degradation.
This case study describes a four story federal building constructed in 1960. The building enclosure consists of a reinforced concrete structural frame with masonry infill walls. The infill walls are bonded construction with brick veneer and concrete block masonry back-up. In this type of construction, a brick header coursing was installed every 7th course or approximately every two feet vertically. The brick veneer lacked a drainage cavity behind it and was therefore intended as a barrier system.
Building assessments revealed problematic conditions that were fairly common for this era:
1) The brick was not fully grouted to the CMU back up. This created voids in the joint space between the brick and block allowing for the accumulation of intruded water. Test openings revealed that up to 50% of the joint space was voided.
2) The block back-up units were only 4″ thick. This created a condition where the brick header coursings were exposed on the interior face of the wall in a thru-wall fashion. The continuous header coursings also naturally dammed any intruded water, which would subsequently migrate inward to the interior face of the wall. In those cases where the casting holes in the brick were not grouted solid, water would continue to move downward inside the wall assembly.
3) The CMU backup was a ‘lightweight’ type of block. As such, it has a very porous matrix and variegated surface. A solvent-based bituminous coating was originally applied to the interior face of the CMU and exposed headers. This thin coating lacked the bridging ability to completely seal the surface and any hairline cracks of the masonry joints.
4) Continuous steel brick relief angles were installed approximately 4″ below each floor level. The steel angles formed a barrier to any intruded water behind the brick. Although thru-wall flashing was originally installed to divert any incidental intruded water to the exterior, exterior interfaces were sealed with caulking which restricted the release of water.
Other deficiencies associated with wall assemblies were also observed. They included:
- Systemic cracking occurred at the brick and associated joints. Joint cracking varied from hairline fractures to more significant separations and degraded joints.
- Sealants at the brick relief angles and relief joints were significantly degraded.
- Thru-wall flashing joints below granite panels are sealed restricting water release.
- Caulking at windows exhibited systemic cohesive failure.
- Interior plasters were severely degraded at walls and ceilings.
Flood testing revealed that water was exploiting the deficiencies of the exterior brick veneer. Entry was associated with defective caulk joints, cracked brick, and cracked mortar joints. The most significant intrusion was associated with floor joints – that is, the horizontal joints of the brick relief angle and the brick relief joint. Water that intruded into the wall assembly was transported to the interior by the thru-wall header coursings. Where grouting of the brick casting cores was incomplete, water was able to continue downward inside the wall assembly. It was then expressed on interior surfaces at various other weak links in the masonry such as the header joints and surface defects.
It was recognized early on that conditions such as deteriorated mortar and sealant joints were readily correctable. But these conditions alone would not address the underlying cause of chronic moisture intrusion, which by 2012 had resulted in widespread mold and degraded interior plasters. A comprehensive solution also demanded attention to the hairline brick cracks and the problematic bonded header courses. Hygrothermal studies also showed that the interior bituminous coating hindered drying and would potentially contribute to premature degradation of brick and mortar.
Many buildings of similar construction are currently protected or are under review for restoration and preservation. This study exemplifies the importance of identifying all probable failure mechanisms, not just the physical conditions per se. Thorough forensic assessments are critical in determining project costs, feasibility, and prioritization. Failure to identify chief deficiencies can seriously jeopardize the project’s success, resulting in greater restoration costs, reduced public support, and diminished funding. In this case, restoration would be best served through a cost-effective, three-tiered strategy of a) prioritized repairs of sealant & mortar joints, damaged brick, and bonded header courses; b) removal of interior bituminous coatings; and c) restoration of interior plaster walls to accommodate safe inward drying.