Concrete Spall Repair
Lucky you live Hawaii!
(Even if you do dwell or work in a concrete structure)
Many of Hawaii’s buildings are of concrete or concrete block construction. Unfortunately from a corrosion viewpoint, steel reinforcing is an integral structural component of each. Hawaii’s salt laden environment (and especially our cooling trade winds that pickup the ocean spray) promotes the intrusion of chloride (i.e., salt) into the concrete. Subsequently the embedded reinforcing steel rusts for the same reason our cars rust, especially so the closer the location is to the ocean.
Rust occupies more volume than the originating steel, thus when the expansive forces of the rusting rebar exceeds the tensile strength of the surrounding concrete, the concrete pops or delaminates or spalls. Depending upon the location of the spalling concrete, a life safety situation may result.
Rusting rebar is common along the edges of our exposed concrete corridors and lanais and at the corners of concrete block walls. Rusting rebar is most always the cause of the spalling. Most of us have seen spalling concrete, especially on the corridor and lanai edges of our buildings, chunks of which can fall on a person or a vehicle. Fortunately, it is rare that a person is in the wrong spot at the same time a chunk of concrete falls. Nonetheless, spall repair should not be put off. The continuing delimitation and subsequent repair cost only increases.
The repair is conceptually easy – remove the delaminated concrete, chip around the exposed rebar to remove chloride contaminate concrete, apply corrosion inhibitors and rusts converters, and patch.
While the repair is conceptually easy, it is technically challenging and not something that should be an afterthought when painting a building. An important key is to ‘chase’ the rusted rebar, including removing chloride-contaminated concrete from behind the rebar and several inches to the right and left to expose clean rebar. This is an often omitted step, especially during painting operations due to the unavailability of pneumatic chipping equipment. It is the reason that many spall repair efforts come up short. Chipping behind rebar is hard work, unfortunately if this step is not performed properly, spalling will reoccur sooner than later.
Additional steps include saw cutting around the chipped out area to improve the mechanical bond, applying a chloride inhibitor to mitigate future rusting, applying a proper bonding adhesive, and patching with a polymer modified mortar.
We perform both large jobs (hotels, condominiums and office buildings) and small jobs (residences as well as individual concrete lanais). The following illustrations are our prior advertisements showing a sampling of our larger concrete spall repair projects.
While the advertisements depict some of our larger projects, we perform spall repair on many smaller jobs, including residential.