Common surface cracks
Fine hairline cracks in plaster often come from drying shrinkage or temperature changes. They are usually cosmetic but can let water in if left untreated.
When to be careful
Wide cracks, cracks that grow, stepped cracks in brickwork, or cracks with exposed rusting steel should be assessed by a qualified structural consultant.
Repair approach
Repairs generally involve cleaning the crack, filling or bridging it with a suitable material and finishing with a protective coating.
Keep a record
Photograph the crack with a date and a measuring scale. It helps professionals judge whether it is stable or moving.
This article is general guidance. Every building is different, so a site inspection is the best way to decide the right solution.