Why is my ceiling paint patchy?
Patchy ceilings come from lap marks, uneven porosity or stains bleeding through — three different faults that look similar from the floor and need different fixes.
- Difficulty
- beginner
- Time
- 30 min
- Read
- 3 min
- Safety
- caution
Short answer
Look at the pattern. Rectangular patches that follow how you worked are lap marks from letting the edge dry. Random dull or shiny areas are uneven porosity, usually over filler or old repairs. Brown or yellow patches coming back through are stains, and only a stain-blocking primer stops those.
A ceiling shows every fault because it is lit from below at a shallow angle by every light in the room. The same wall would look fine. That is why ceilings get repainted more often than they need to be — the paint is often correct and the problem is where the joins fell.
Safety
Step by step
- Look along the ceiling from a low angle before deciding.Stand at one end and look across it towards a window. The pattern tells you the cause, and the three causes look identical from directly below.
- Identify lap marks by their shape.Straight-edged patches in rectangles roughly the size of the area you rolled at a time. They happen when the edge of the wet area dries before the next section joins it, so the overlap has two coats and the middle has one.
- Fix lap marks by keeping a wet edge and working the short way.Work across the shorter dimension of the room in bands, joining each band to one that is still wet, and do not stop halfway through a ceiling. Cutting in the whole perimeter first and then rolling can itself cause a picture-frame effect if the cut-in dries first.
- Identify porosity by where it is.Dull or flat patches over old repairs, filler, or where a previous ceiling was patched. The paint has soaked in there and sits on the surface elsewhere, so the sheen differs even though the colour matches.
- Seal porous patches rather than adding another full coat.Spot-prime the absorbent areas, let them dry, then apply a full coat over the whole ceiling. Another full coat without sealing produces the same patchiness one layer higher.
- Identify stains by their colour and their persistence.Brown, yellow or grey marks — often from an old leak, nicotine or smoke — reappear through each new coat, sometimes within hours. Water-based paint alone will never bury them.
- Use a stain-blocking primer on stains, and find the leak first.A stain block seals the mark so it cannot migrate. But if the stain is from an active leak, blocking it hides evidence of a live problem. Establish that the source is fixed and the area is dry before covering it.
- Use a matt finish for ceilings.Any sheen on a large flat surface lit from below amplifies every irregularity in the plaster and every lap. Matt hides what silk shows.
Common mistakes
- Painting over a water stain without checking the leak is fixed. — The stain returns, and you have removed the thing that was telling you the roof or the pipe is still letting water in.
- Stopping halfway across a ceiling for a break. — The edge dries and the join shows permanently. Plan the ceiling as one continuous piece of work.
- Using silk or a sheen finish on a ceiling. — It reflects the light along the surface and makes every undulation and lap mark obvious.
Questions people ask
Why does it look fine when wet and patchy when dry?
Wet paint is uniformly glossy, which hides differences in absorption. As it dries, the areas that soaked in go flatter than the areas that did not, and the difference appears.
Will a third coat fix it?
Only if the cause is coverage. If it is porosity or stains, a third coat will look exactly like the second, because the cause is underneath the paint rather than in it.