Why Do Walls Crack?

Not all cracks mean the same thing. Hairline cracks in plaster, especially in new construction, are often related to normal shrinkage as materials cure and are usually cosmetic.

Diagonal cracks, particularly those radiating from the corners of doors and windows, can indicate differential settlement — parts of the foundation moving at different rates, often linked to soil conditions.

Cracks that are wider at one end (tapering) suggest ongoing movement rather than a one-time event, and are worth monitoring or having assessed.

Horizontal cracks in walls, especially retaining walls, can indicate pressure from soil or water behind the wall and deserve prompt attention.

As a general guide: cracks wider than about 3mm, cracks that are growing, or cracks appearing alongside doors/windows that no longer close properly are signs to have a structural engineer inspect the building rather than simply patching the plaster.

If a crack appears suddenly and is accompanied by other warning signs — sagging floors, leaning walls, or doors jamming — treat it as urgent and seek an immediate professional assessment.