NANDIX Repairs · Mason; a structural engineer for wide or growing cracks
Cracks in walls and plaster
Most thin cracks are in the plaster and come from shrinkage or temperature. Wide, diagonal or growing cracks can mean the structure is moving and need an engineer.
Stop and call a professional: Wide (over 5 mm), diagonal or growing cracks, cracks in beams, columns or the slab, or doors that suddenly stick: call a structural engineer before any repair.
What usually causes it
- Hairline plaster cracks from drying shrinkage, usually in the first year or two.
- A straight crack where a brick wall meets a concrete column or beam: the two materials move differently.
- Diagonal cracks from the corners of doors and windows, often from settlement.
- Cracks that keep getting wider: foundation movement, overload or water under the foundation.
What you can check yourself
- Measure the width: hairline (under 1 mm), medium (1–5 mm), wide (over 5 mm).
- Draw a pencil mark at each end and write the date. Check again after a month: has it grown?
- See if doors and windows nearby have started to stick.
- Check if the crack goes right through the wall (visible on both sides).
Parts to ask the shop for
- Crack filler or acrylic sealant for hairline cracks
- Fibre mesh tape or chicken mesh for cracks at column and wall joints
- Polymer-modified repair mortar for wider plaster cracks
- Wall putty and primer before repainting
Take the old part or a photo of it: sizes and threads must match.
What to ask the worker
- Is this a plaster crack or a structural crack? How do you know?
- Will you open the crack into a V-groove and fill it, or only paint over it?
- For joints with columns: will you fix mesh across the joint before re-plastering?