Typical brick built apartment block in Sydney's south, constructed in the early 1960s. After fifty odd years the balconies started to show signs of ageing with vertical and

horizontal cracks appearing over the past decade causing the balconies to become unstable.

Cause

With more than one of type of cracking present, multiple causes were likely.

Firstly, the horizontal or zig zag cracks in the brickwork were caused be deflection of the concrete slab over time. As one side of the balcony slab moved differently to the other side the tensile strength of the brickwork weakened causing the cracking.

The second problem was a little less obvious to the untrained eye. Almost random vertical cracks were evident, starting from the bottom of the wall and then tapering in width at the top and stopping three courses from the top. The cause of these verical cracks is similar to concrete spalling. To keep the wall bonded to the concrete slab, during initial build, steel rebar is set into the concrete about 600mm high. After concrete sets, the bricklayer lays his brick over these bar increasing the lateral strength of the wall.

Solutions

#1 Create masonry full length of balconies and return externally. Re-point brickwork to match original.

#2 Expose the corroded steel rebar and remove loose material. Treat steel with appropriate products and coatings or install complete new rebar. then re-brick to match.