Rebar corrosion

Reinforced concrete has steel bars inside it, the reinforcement, which give strength to columns, beams, slabs and balconies. As long as the concrete around them is healthy and thick enough, it protects them. But when water gets in, from a leaking roof, a bathroom leak or a crackCrackA split or gap in render, concrete, a wall, a coating or wood. Fine cracks are usually only on the surface; ones that grow, keep reopening or run diagonally need attention., the bars start to rust over the years.

Rust takes up more room than steel. So the bar swells and pushes on the concrete, which cracks and falls away in pieces. The signs are cracks in a straight line on ceilings, balconies or columns, brown rust stains, and renderRender (plaster)A layer of mortar (sand, cement or lime, and water) spread over brick or concrete to give a wall a straight, sound surface ready for paint or tiles. or concrete coming away and leaving the bars visible.

The repair starts by opening up the area back to sound concrete. The bars are cleaned of rust and coated with an anti-corrosionAnti-corrosion coatingA protective coat brushed onto steel reinforcement, once the rust has been cleaned off, so the bars don't keep rusting before they are covered with new material. primerPrimerThe thin first coat that goes on before the main material. It binds dust, seals the pores and helps paint or waterproofing stick firmly., and the missing section is built back up with repair mortarRepair mortarA special cement-based mortar for rebuilding concrete that has cracked or fallen away, for example around rusty steel. It bonds well to old concrete and seals the reinforcement in.. But the repair only lasts if the water that caused the rust is stopped. If the corrosion is widespread or affects columns and beams, a structural engineerStructural designAn engineer's study that checks whether a building can take a change, such as an opening in a load-bearing wall, and sets out how it is done and how it is strengthened. needs to see it.