When Rusty Steel Shows Through

Inside slabs, beams, columns and balconies there are steel bars, the reinforcement. As long as the concrete around them is sound and thick enough, it protects them. But when water gets in for years, from the roof terraceFlat roof (roof terrace)The flat concrete roof on top of a building. It is the most common kind of roof in Greece and the part that takes the most sun and rain., a balcony, the bathroom upstairs or a dripping pipe, the bars rust.

Rust takes up more room than steel. So the bar swells and pushes the concrete outwards: first 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. opens along it, then the plasterRender (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. falls and the bars show. This is called rebarRebar corrosionRust on the steel bars inside concrete. Rusting steel swells, cracks the concrete around it and makes it fall away in pieces, leaving the bars exposed. corrosion.

The repair, step by step

The two jobs on ceilings with rusty steel show the same order.

1. Opening up. The crack or damaged area is opened up until the rusty bar and sound concrete around it can be seen. In the bedroom, a crack that looked thin was opened along the whole length of the bar.

2. Cleaning. Loose rust and crumbling concrete are removed, so the next material sits on a clean surface.

3. Protecting the bars. Every exposed bar gets 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. coat so it doesn't keep rusting. On the second ceiling, where a large area of plaster had fallen, the coat was red and you can see it clearly on every bar.

4. Building it back. The missing section is filled 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., which covers and seals in the bars on every side.

5. Finishing. The surface is filled, sandedSandingSmoothing a surface with sandpaper or a power sander to remove bumps, loose old paint or gloss, so the new paint or varnish grips well and comes out smooth. and painted along with the rest of the ceiling, so the spot doesn't stand out.

What decides whether the repair lasts

• The water has to stop. If the roof or the bathroom above keeps letting water through, the rust will start again.
• The bars have to be properly covered. The new material must cover them completely, not just hide the crack.
• The bars mustn't be badly eaten away. If a bar has lost much of its thickness, if the damage covers a large area, or if it is on a beam, column or balcony, 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 first. It may then need more than repair mortar.

Questions to ask before work starts

• Will the area be opened up until clean steel and sound concrete show?
• What will protect the bars, and what will the section be rebuilt with?
• Where is the water that rusted them coming from, and who will stop it?