The shape, direction and width of a crack say a lot about what caused it. This guide covers the common types of cracks in walls, what they usually indicate, and how structural cracks are fixed. For a quick check of whether yours is serious, see are cracks in walls serious?
Hairline cracks
Very fine cracks, often in plaster or render, usually caused by shrinkage or minor seasonal movement. Generally cosmetic and fixed when repainting.
Vertical cracks
Straight up-and-down cracks, often near the middle of long walls or at junctions. Commonly caused by shrinkage or thermal movement. If wide or growing, they can indicate footing movement.
Diagonal cracks
Cracks running at an angle, often from the corners of windows and doors. These are a classic sign of differential footing movement, where one part of the building moves more than another. Common on Sydney's reactive clay soils.
Stepped cracks
Cracks that follow the mortar joints of brickwork in a staircase pattern. Like diagonal cracks, they usually point to movement in the footings or the wall.
Horizontal cracks
Cracks running along a wall, often along mortar joints. In brick walls these can indicate corroded wall ties or the outer skin of brick moving away from the structure. In retaining or basement walls, they can mean soil pressure. Horizontal cracks deserve prompt inspection.
Cracks above windows and doors
Cracks starting at the corners of openings, sometimes with rust staining, often mean a corroded steel lintel is expanding and lifting the brickwork.
Dangerous wall cracks
- Wider than about 5mm, or growing.
- One side of the crack out of line with the other.
- Walls bulging or leaning.
- Doors and windows suddenly sticking.
- Cracks through bricks rather than around them.
How structural cracks are fixed
- Diagnose the cause, with an engineer for significant cracking.
- Fix the cause: drainage, leaking pipes, trees, lintels, wall ties or footings.
- Repair the wall: helical crack stitching, brick replacement, epoxy injection or rebuilding sections.
- Make good with matched mortar, render and paint.
Crack repairs in Sydney
See our wall and structural crack repair service.
Frequently asked questions
Which wall cracks are dangerous?
Cracks wider than about 5mm, growing cracks, cracks where one side is out of line, bulging walls and horizontal cracks in brick walls should be inspected promptly.
What do diagonal cracks from windows mean?
Usually differential footing movement, or sometimes a corroded lintel above the opening.
How do you fix structural cracks in walls?
Fix the cause first, then repair the wall with crack stitching, brick replacement or injection, and make good the finishes.
