How to fix cracked brickwork (and when a crack is serious)

Cracks in brickwork are common in Melbourne, mostly because of our reactive clay soils that swell and shrink with the seasons. Some cracks are harmless. Some are telling you something has moved.

When a crack is minor

Fine hairline cracks in the mortar, especially ones that follow the joints, are usually cosmetic. They often open and close slightly through the year as the ground gets wet in winter and dries out in summer.

• Cracks thinner than about 2mm that sit in the mortar lines.
• Cracks that have been there for years and have not grown.
• A single short crack near a window or door corner that is not moving.

These can often be raked out and repointed so they look right again.

When a crack is serious

Watch for cracks that suggest the wall or footing has shifted, not just the mortar.

• Stair-stepping cracks that climb diagonally through the bricks themselves.
• Cracks wider than about 5mm, or ones that are clearly wider at the top or bottom.
• Bricks that have shifted out of plane so the wall is no longer flat.
• Doors and windows that have started sticking at the same time.

Those patterns point to footing movement, subsidence, or a moisture problem under the slab. Filling them without fixing the cause just hides the problem until it comes back wider.

What to do next

The honest answer is that diagnosis matters more than the patch. A good repair starts with working out why the wall cracked.

• Monitor a crack by marking the ends with a pencil and a date, then check it over a few months.
• Get the cause looked at if it is growing, stepping through bricks, or letting water in.
• Repoint or rebuild the affected section once the movement is understood and, where needed, the footing is addressed.

If you are not sure which type you have, send us a photo of the crack and your suburb. We can usually tell from a clear picture whether it is cosmetic or worth a proper look.