Fresh plaster looks ready long before it actually is, and painting too soon is one of the most common ways a smart new finish gets ruined. Here is what really happens as plaster dries, how long to wait in a typical Scottish home, and how to tell when it is genuinely ready for paint.
As a rule of thumb, allow around 5 to 7 days for a skim over existing plasterboard, and up to 3 to 4 weeks where plaster has been applied thickly over brick, block or bonding coats. The surface can feel dry in a day, but moisture is still working its way out from underneath.
Drying is not about time alone. It depends on the thickness of the plaster, the background it was applied to, the room temperature and how well the moisture can escape into the air. A cold, closed-up room in a Fife winter will dry far slower than a warm, ventilated one in June.
Wet plaster is a patchy brown, sometimes darker in the corners and around window reveals where it dries last. As it cures it turns an even, pale pink or almost white across the whole wall. That uniform colour is your best visual signal.
Ventilation matters more than heat. Crack windows open during the day to let damp air out, and keep internal doors open so air can move through the property. In older Edinburgh tenements and stone-built Borders cottages, walls hold moisture longer, so patience pays off.
You can run central heating gently, but avoid blasting a room with heat or aiming a dehumidifier or fan heater straight at fresh plaster. Forcing the surface to dry faster than the core can cause cracking and a powdery finish. Steady, low warmth with good airflow is the safe approach.
New plaster is porous and will drink in ordinary paint, so the first coat should be a mist coat: emulsion watered down by roughly 30 to 50 percent. This soaks in, seals the surface and gives your topcoats something to grip.
Do not use most one-coat or heavily branded 'new plaster' paints as a substitute unless the tin specifically says it suits bare plaster, and never start with a vinyl or silk finish straight onto fresh plaster. Once the mist coat is fully dry, usually within a few hours, you can apply two topcoats as normal.