Problem
A waterfront basement carpark with widespread soffit spalling and rust staining — chloride-driven corrosion from marine exposure and a leaking podium deck above. Two earlier rounds of patch repairs had failed at their perimeters within five years: the classic ring-anode pattern, where patching shifts the corrosion cell next door instead of stopping it.
Diagnosis
Chloride profiling confirmed contamination above threshold at reinforcement depth across large zones — the condition where patch-and-coat cannot arrest corrosion. Half-cell potential mapping distinguished actively corroding zones from passive ones, letting the repair strategy match intervention to condition instead of treating the whole structure identically.
Method
Three-tier strategy, engineered with a corrosion specialist: conventional break-out and repair in low-risk zones; galvanic (sacrificial) anodes embedded at patch perimeters in moderate zones to kill the ring-anode effect; hybrid anode corrosion protection across the actively corroding high-chloride zones. Upstream, the podium deck membrane was replaced to cut the chloride-bearing water at its source. Level-by-level staging maintained resident parking throughout.
Outcome
A corrosion-management outcome rather than a patch cycle: monitored protection with a 25-year design intent, documented for the OC’s maintenance plan, and a completion report the committee can hand to any future engineer.