Almost every building develops cracks. Most are harmless, caused by plaster shrinking as it dries or by daily temperature changes. Some, however, are the first visible sign of a structural problem. Knowing the difference can save you both money and worry.
Usually not serious
- Fine, hairline cracks in plaster, often in a random or map-like pattern
- Cracks along the joint between a wall and a column or beam, where different materials meet
- Cracks that appeared once and have not changed in width or length
Get them checked
- Diagonal cracks running from the corners of doors and windows
- Cracks wider than about 3 mm, or ones you can fit a coin into
- Cracks that are growing over weeks or months
- Any crack in a column, or across the underside of a beam or slab
- Cracks with rust stains, which suggest corroding reinforcement
- Cracks together with sticking doors, sloping floors or gaps at skirting
A simple way to monitor a crack
Mark both ends of the crack with a pencil and write the date beside it. Photograph it next to a ruler. Check again after a few weeks. If it has grown longer or wider, it is active and should be inspected by a structural engineer.
What an assessment involves
An engineer maps the cracks, looks at their pattern and location, and relates them to how the building carries its loads. Non-destructive tests may be used to check the concrete and reinforcement. The cause matters, because the right repair for a settlement crack is very different from the right repair for a shrinkage crack.