Question
General requirement for Civil Engineering Works in 1992 Edition, Clause 15.09 details that tying wires for strengthening adjacent to and above Class F4 and F5 closes must be stainless steel wires. Give genuine reasons?

Answer
If plain steel tying wires are utilize for reinforcement adjacent to Class F4 and F5 closes, it poses problem of rust staining that may impair appearance of uncovered concrete surfaces. Speed of corrosion of plain steel tying wires is alike to regular steel reinforcement. Yet, for tying wires with extremely tiny diameter, upon long exposure it stands a high possibility of rusting finally and this rust will stain formwork and significantly involve concrete finish. Then, stainless steel tying wires are specified for locations in vicinity of high excellence of finishes to keep away from rust staining by corroded typing wires.