Spalling (concrete)

Spalling is concrete flaking, chipping or breaking away from a surface, exposing the material (or the steel) beneath. The classic cause is corrosion of the reinforcing steel inside: when moisture and chlorides reach the rebar it rusts, and because rust takes up more volume than the original steel, it expands and forces the concrete off from within — sometimes called 'concrete cancer'. In the UAE it's accelerated by coastal salt air and chloride-laden ground or tanker water, and you see it most on balcony edges and soffits, car-park decks, and exposed facade concrete. It's different from efflorescence (a harmless-looking salt bloom) — spalling is structural and gets worse if ignored, because once rebar is exposed it corrodes faster. A proper repair is not cosmetic filler: you break back to sound concrete, treat or replace the corroded steel, rebuild with a bonded repair mortar, then fix why water reached it (waterproofing, drainage). Bodies like the American Concrete Institute publish the repair principles. If a snag or survey turns up spalling, treat it as a structural item for a finishing and snagging team or a specialist to assess, not a patch-and-paint job.