How do you treat exposed rebar in damaged concrete?

Treating exposed rebar is the most critical step in concrete repair, and done properly it follows a five-stage protocol. First, we break out the concrete around the bar — typically 15-20mm behind it — because corrosion always extends further than the visible damage. Second, the steel is cleaned back to bright metal (Sa 2.5 standard) by grit blasting or mechanical wire brushing to remove every trace of rust; painting over corrosion simply traps it. Third, where the bar has lost more than around 10% of its cross-section, a structural engineer must assess whether supplementary reinforcement is needed. Fourth, the cleaned steel is coated with a zinc-rich passivation primer (such as Sika MonoTop-910 N) that protects it against future corrosion — this is the step DIY repairs almost always miss, and the reason they fail within a couple of years. Finally, the section is reinstated with a polymer-modified structural repair mortar compliant with BS EN 1504-3, compacted around the bar so no voids remain. If you only need a short-term hold, sealing exposed rebar with a rust converter and cementitious fairing coat can slow corrosion, but it is not a repair: once rebar is exposed and rusting, the expansion of the steel (up to seven times its original volume) will keep cracking the surrounding concrete until the corroded material is removed and the bar is properly passivated and re-covered.