Flashing is when parts of a dried wall reflect light differently to the rest, showing as duller or glossier patches even though the same paint was used throughout. It is a coverage and absorption issue rather than a colour issue, and it usually only becomes obvious once the coat has fully cured and the light catches it.
Filled areas, patched plaster and bare new plasterboard all absorb paint differently to the surrounding painted surface. Without a mist coat or appropriate sealer over those patches first, the topcoat sinks in unevenly and dries to a different sheen level in those spots.
Rolling the same area more than once while it is drying, or applying an inconsistent film thickness across a wall, both leave sheen variation behind, particularly with mid-sheen and satin finishes where the difference is more visible than on a flat matt.
New plaster, filled patches and any repaired sections are sealed with an appropriate mist coat or primer matched to that surface before the finish coats go on, so the whole wall absorbs and reflects light in the same way once finished.
Some minor variation can settle slightly, but genuine flashing from uneven suction does not usually disappear on its own and normally needs an extra coat.
New plaster is the most common cause, but old filled patches, previously stained areas and inconsistently primed surfaces can all cause the same effect.
Yes, usually with a further full coat over the sealed and evened-out surface, checked carefully in raking light before it is signed off.
Send a photo of the wall taken in low, raking light and we will explain what the pattern suggests.
Flashing comes from uneven suction or inconsistent application, and the fix is proper sealing before the finish coat, not a heavier topcoat.
Speak to a Hampshire commercial decorating contractor that turns up, communicates clearly and delivers a finish that lasts.
