Patchy Paint And Roller Marks

What's happening?

Patchiness is almost always about how evenly the wall absorbed the paint rather than how much paint went on. Where the surface is more porous — filler, a skimmed repair, bare plaster, a sanded-through area — it pulls more binder out of the wet coat and dries duller and darker than the rest. Decorators call the darker window round the edges of a wall picture framing: it happens because the brushed-in cut line lays a different film thickness from the roller. Lap marks come from rolling into an area that has already started to set. All three are finishing faults, they will not correct themselves, and adding a spot coat over the worst patch usually makes the difference more obvious rather than less.

What usually causes it?

• Filler and patch repairs left unprimed, so they absorb more than the wall around them
• No mist coat on new plaster, giving uneven suction across the surface
• Cutting in the edges with a brush a long time before rolling the field, so the two dry differently
• Letting the roller edge set before overlapping the next pass, leaving a lap line
• Over-spreading a coat to make the tin go further, leaving the film too thin to level
• Rolling in strong low sunlight or with a heater running, so the paint sets faster than it can be laid off
• Different batches of the same colour used across one wall

When should you call a painter and decorator?

Call a painter and decorator when a full extra coat has not evened it out, when the wall has heavy suction variation from repairs, when the colour is a deep or strongly pigmented shade that shows every lap, or when the room has a large uninterrupted wall that is hard to keep a wet edge across. Getting a flat finish on a difficult wall is skill and sequencing, and it is the thing homeowners most often call a decorator back for.

What will the painter and decorator actually do?

• Read the wall for suction variation and identify which areas need sealing before painting
• Prime or mist-coat the repairs and bare areas so the whole wall absorbs evenly
• Fill, sand and de-nib so the surface itself is not creating shadow lines
• Cut in and roll each wall as one operation, keeping a wet edge across the full height
• Lay off the final coat in one direction and check the finish in raking light before leaving