Usually 7 to 14 days. Here is how to tell when it is actually ready, and why rushing it ruins the job.
Allow 7 to 14 days for new plaster to dry before you paint it. A single skim coat in a warm, ventilated room in summer might be ready in a week. A thick coat, a cold room, or the middle of a Devon winter can take three weeks or more.
Do not go by the calendar. Go by the colour.
The plaster tells you. You just have to look at it.
Fresh plaster is dark brown. As it dries it goes a uniform pale pink. When the whole wall is an even light pink with no dark patches, it is dry.
Patches that are still darker are still damp, usually corners, behind radiators, and the bottom of walls. If any remain, wait.
Dry plaster feels warm and dry to the back of the hand. Damp plaster feels cool.
Open windows and let air move. Do not put a heat gun or blow heater on it, drying it too fast causes cracking.
Cold, damp air holds less moisture. A job that dries in a week in July can take three in January.
A skim over existing plaster dries far quicker than a full re-board with backing coat and skim.
New plaster is porous and thirsty. If you go straight in with normal emulsion, the plaster sucks the moisture out of the paint before it can bond, and the paint peels off in sheets a few months later.
The fix is a mist coat: ordinary matt emulsion thinned with water, roughly 70% paint to 30% water, brushed or rollered on as your first coat. It soaks in and seals the surface. Once that is dry, you can paint normally.
Use a cheap matt emulsion for the mist coat, not a vinyl silk and not a "one-coat" paint. Vinyl and silk paints form a film rather than soaking in, which defeats the point.
Paint applied to plaster that is still damp traps the remaining moisture behind an impermeable film. The moisture has nowhere to go, so it pushes the paint back off the wall. You get bubbling, flaking and peeling, usually a few weeks later, once you have put the furniture back.
It is a genuinely miserable job to put right, because the paint has to come off and the wall has to dry out properly anyway. Waiting the extra week is always cheaper.
The ones we get asked most.
New plaster typically needs 7 to 14 days to dry before painting. A thin skim in a warm, well-ventilated room may be ready in a week, while a thick coat, a cold room or winter conditions can take three weeks or more. Judge by colour rather than by the calendar.
Fresh plaster is dark brown and turns a uniform pale pink as it dries. When the entire wall is an even light pink with no darker patches remaining, particularly in corners, behind radiators and at the base of walls. It is dry and ready to paint.
A mist coat is ordinary matt emulsion thinned with water, roughly 70% paint to 30% water, applied as the first coat on new plaster. New plaster is porous and will draw the moisture out of undiluted paint before it can bond, causing it to peel later. The mist coat soaks in and seals the surface. It is essential, and it should be a cheap matt emulsion, not vinyl or silk.
No. Forcing plaster to dry quickly with heat guns or blow heaters causes it to crack and can weaken the bond. Ventilation is the right approach, open windows and let air circulate naturally.
Painting damp plaster traps the remaining moisture behind an impermeable film of paint. The moisture pushes the paint back off the wall, causing bubbling, flaking and peeling, usually within a few weeks. Putting it right means stripping the paint and letting the wall dry out properly anyway.
Send a photo on WhatsApp and we'll tell you straight, including if the answer is "leave it alone".