Lagos, Port Harcourt and Calabar share a structural disease — chloride-induced reinforcement corrosion. The salt comes from the air, the rain, and from sub-grade brackish water. It attacks the steel rebar through whatever cover concrete it can get past.
What you see
The first visible symptom is brown staining on the soffit of slabs or on column faces. By the time you see it, you have already lost between 5 and 15 percent of the steel section behind it.
What works
Sacrificial galvanic anodes, embedded into the concrete cover, draw the corrosion current away from the rebar. Anti-carbonation coatings on the external face slow the rate of chloride ingress.
What does not work
Painting over rust stains. Hacking off the cover concrete without addressing the corrosion mechanism. Both buy you 18 months and then the staining returns, worse.
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