Seal new plaster with a diluted mist coat before painting, once it's fully dry, to stop patchy colour later.
MC-01Check the plaster is fully dryNew plaster needs to dry out fully before you paint it, usually 4-6 weeks depending on thickness, room temperature and how well it's ventilated. Look for an even pale pink or grey colour all over the wall or ceiling. Darker, damp-looking patches mean it isn't ready yet. Painting over damp plaster traps moisture in and causes bubbling or peeling later.
MC-02Clear and protect the roomMove furniture out or into the middle of the room and cover it with dust sheets. Cover the floor and skirting boards too, since mist coat splashes easily. Open a window or door to keep air moving while you work and while the paint dries.
MC-03Snag and fill small marksRun a hand over the new plaster and check for small nicks, screw holes or gaps where the plaster meets skirting, coving or door frames. Fill these with a flexible multi-purpose filler using a small filling knife. Leave to dry fully, then rub over lightly with fine sandpaper.
MC-04Mix the mist coatUse an ordinary matt or contract matt emulsion, never vinyl silk, for a mist coat. Thin the first coat to roughly 70% paint and 30% water — about 1.5 litres of water stirred into 5 litres of paint. This thin mix soaks into the porous new plaster and seals it evenly, so the topcoat goes on flat and consistent later.
MC-05Cut in the edgesUsing an angled brush, paint a band about 50mm wide around the ceiling line, skirting, window and door frames, and into corners. This gives the roller a clean edge to work up to and stops the diluted mix pooling in tight angles.
MC-06Roll the mist coat onto the main areasLoad a medium-pile roller and work in sections roughly 1m square, top to bottom. Overlap into the still-wet edge of the last section so you don't get visible join lines. Keep the coat thin and even; it's meant to soak in, not sit on top.
MC-07Let it dry and check the surfaceLeave the mist coat to dry fully, usually 2-4 hours, keeping the room ventilated. Once dry, look across the wall or ceiling under a raking light. Duller, flatter patches show where the plaster soaked up more paint than the rest — these need another coat.
MC-08Apply a second mist coat if neededIf flat or patchy areas remain, mix a slightly stronger second coat at around 80% paint to 20% water. Apply the same way, cutting in first then rolling. Most new plaster needs two mist coats before it's ready for a proper topcoat.
MC-09Clean up and leave to dryRinse brushes and rollers straight away in water, since emulsion is water-based. Wipe up any splashes on skirting or floor covers before they dry. Peel off masking tape while the paint is still slightly tacky, not once it's rock hard. Leave the room ventilated for at least 24 hours before applying your chosen topcoat.