Concrete cancer or subsidence? Your guide to what's happening to your home, before you spend a dollar

A new crack in a wall is unsettling, and the internet is quick to tell you the worst. The reality is calmer. The large majority of cracks in Australian homes are cosmetic: shrinkage in render or plaster, seasonal movement in reactive clay soil, or paint splitting over an old joint. They look alarming and they are usually harmless.

A smaller group of cracks are a sign of something structural, which is when the footing or slab your house sits on has moved. The tell-tale differences are the width of the crack, whether it runs on a diagonal from window and door corners, whether doors and windows have started to jam, and whether the crack is still growing month to month. Those are the ones worth an engineer's eye.

Concrete cancer is a separate problem again. It is not about the ground moving; it is the steel reinforcement inside concrete rusting, expanding and blowing the concrete apart from the inside. It shows up as rust stains, bubbling render and lumps of concrete falling away, most often on balconies, in basements and around coastal buildings. The guides below explain both problems in plain language, grounded in Australian engineering guidance, so you can tell the difference and act proportionately.