Cut in neatly where the wall meets the ceiling

Paint a crisp, straight line where wall meets ceiling using masking, a sash brush, and a steady hand.

CI-01Clear the room and protect surfacesMove furniture away from the walls or cover it with a dust sheet. Lay dust sheets along the skirting on both walls you're working near, as drips fall further than you'd think. Open a window for ventilation if you're using solvent-based paint.

2 each · Cotton dust sheets

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CI-02Check the junction and fill any gapsRun a finger and your eye along the wall-ceiling line looking for hairline cracks, gaps, or old flaking paint. On older lath and plaster ceilings, small cracks along this line are common because the ceiling moves slightly with the seasons – use a flexible decorator's caulk here, not a rigid filler, or the crack will just reopen. On plasterboard ceilings (timber or metal stud, or dot-and-dab walls) any gap is usually just a poor original tape joint – caulk works fine there too. Smooth the caulk with a wet finger and let it skin over before painting.

1 tube (310ml) · Flexible decorator's caulk

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1 each · Filling/caulking gun

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CI-03Mask the line if you're not confident freehandStick low-tack masking tape along the ceiling, right up to the edge, and press it down firmly with your finger or a filling knife blade so paint can't creep underneath. Do short lengths at a time so the tape stays straight. Skip this step entirely once you trust your hand – tape takes time and never gives quite as sharp a line as a good brush.

1 roll · Low-tack masking tape, 25mm

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CI-04Load your brush correctlyUse an angled sash brush – 25-38mm is right for most rooms. Dip only a third of the bristle length into the paint, then tap off the excess against the side of the tin or tray. An overloaded brush is the main cause of drips and a wobbly line.

1 each · Angled sash brush, 38mm

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1 each · Paint kettle or small tray

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CI-05Cut in along the ceiling edgeStarting in a corner, lay the brush about 5mm away from the line, then draw it towards the edge in one smooth stroke. Work in sections of about 300-400mm at a time along the ceiling, blending each new section into the wet edge of the last before it dries. Keep the brush moving – stopping mid-stroke leaves a hard line.

CI-06Cut in the top of the wallOnce the ceiling line is done, cut in the wall side the same way, working along the top edge where it meets the ceiling. If you're doing a whole ceiling and whole wall in different colours, let the first cut-in dry fully before masking over it to do the other surface, or the tape will lift the fresh paint.

CI-07Adjust technique for textured or uneven ceilingsOn an artex or heavily textured ceiling, a razor-sharp line isn't possible or necessary – dab the brush into the texture at the edge rather than dragging a smooth stroke, and let the line follow the texture naturally. On wavy old lath and plaster ceilings, the wall-ceiling junction often isn't straight either, so work to the actual join rather than trying to force a perfectly level line – it will look more natural and less obviously wrong.

CI-08Remove the tape and check the lineIf you masked up, pull the tape away slowly at a low angle while the paint is still slightly soft – usually 20-40 minutes after painting, but check the tape packaging. Pulling it off once the paint has fully dried can peel paint away with it. Once the tape's off, stand back and check the line in good light; touch up any wobbles with a small brush.

CI-09Clean up and put tools awayWash brushes straight away in warm water for water-based paint, or the correct solvent for oil-based paint, working the bristles until the water runs clear. Fold dust sheets carefully so any drips stay on the inside, and let the room air out while the paint cures.

1 small bottle · Washing-up liquid (for water-based brush cleaning)

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