What causes cracks in plaster?

Hairline cracks are usually nothing to worry about — they happen as plaster dries and the house naturally moves with the seasons. A simple flexible filler and a touch-up of paint usually sorts them.

Larger cracks (more than a few millimetres wide), cracks that follow a stair-step pattern through bricks, or cracks that keep opening up after repair, are different — they can point to movement in the structure, damp, or a poor original plastering job. Worth a closer look.

Cracks at the wall/ceiling joint are very common and are usually solved by fitting coving or a flexible decorator's caulk before painting.

If you're seeing a lot of cracks in fresh plaster within weeks of the job, the original work was likely applied too thick, too fast, or onto an unsuitable surface. That's not something to live with.