Movement, not paint failure
Houses move. Timber framing takes on and gives up moisture through the year, roof structures shift a little with heat, and across much of Melbourne's south-east the clay soils under the slab or stumps swell when wet and shrink when dry. None of that is unusual, and in most homes it is small. But it concentrates at the weak points: where two materials meet, where two sheets of plasterboard join, and at the corners of openings.
Paint is a thin film. It can stretch a little, but it cannot hold a joint closed that the building is opening and closing. That is why the same crack shows up in the same place after every repaint, often within the first change of season.
Why filler alone keeps failing
Standard filler sets hard. That is exactly what you want for a nail hole or a dent, which never moves again. In a moving joint it is the wrong material: the filler is now the most rigid thing in the gap, so when the joint opens, it cracks along one edge or pops out altogether, and the line comes back looking exactly as it did.
The fix depends on where the crack is. At the cornice-to-wall line and internal corners, the gap is raked out and filled with a flexible, paintable sealant that can stretch and recover with the movement. Along a plasterboard join that has opened, the join itself has usually let go, so it needs cutting back and re-taping and setting rather than skimming over. Fine hairline cracks in a sound wall can be filled and sealed in the normal way.
Getting the order right
Crack repair belongs in the preparation, before any topcoat. Flexible sealant needs to cure before it is painted, re-set joints need to dry and be sanded flush, and every repair needs sealing so it does not show through the finish as a dull patch. Quotes that skip this or price it as an afterthought are the main reason a fresh paint job shows the old cracks again.
On our interior quotes, crack and joint repairs are written into the preparation, so you can see what is being repaired before any paint goes on.
When a crack needs a builder first
We are painters, not structural engineers, and some cracks are not ours to cover up. Get the cause looked at by a builder or engineer before repainting if a crack is wide or keeps getting wider, runs diagonally away from the corner of a window or door, steps through the mortar of brickwork outside, or comes with doors and windows that have started sticking.
Painting over those signs does not fix anything and makes them harder to monitor. If we see them during a quote, we will tell you, and we can repaint once the underlying problem has been dealt with.
Outside the house
Cement render cracks too, mostly as fine hairline shrinkage cracking. On sound render those are filled and the wall is coated with a system that can bridge fine cracks, which is covered on our render repair page. Wider or stepped cracks in render or brick are the same story as inside: find and fix the cause first, then paint.
Frequently Asked Questions
Why does the crack above my door keep coming back after painting?
Because the corners of door and window openings are where a house's normal seasonal movement concentrates. Hard filler cannot move with it, so it cracks again. The repair that lasts is raking the crack out and using a flexible, paintable sealant, or re-taping the join if the plasterboard itself has separated, before the walls are painted.
Can a painter fix cornice cracks?
Yes, where the cornice has simply separated from the wall along the join. The gap is cleaned out and filled with flexible sealant so the joint can move without showing. If the cornice itself is loose, sagging or coming away from the ceiling, it needs re-fixing by a plasterer first.
Is a cracked wall a structural problem?
Most fine cracks at joints and corners are normal movement, not structural damage. Have a builder or engineer look before painting if the crack is wide or growing, runs diagonally from a window or door, steps through brickwork outside, or doors and windows have started sticking.
Are crack repairs included in a painting quote?
They should be. Our written quotes itemise the preparation each surface needs, and crack and joint repairs are part of that, so you can see what is being repaired before any paint goes on.