Summary
A skim coat on plasterboard usually dries in two to four days. Skim over a backing coat typically takes one to two weeks, and lime plaster can take several weeks. Plaster is dry when it has turned an even, pale colour with no dark patches.
Typical drying times
- Skim on new plasterboard: 2–4 days
- Skim over existing plaster: 3–5 days
- Backing coat plus finish: 1–2 weeks
- Lime plaster: several weeks, depending on thickness
- External render: follow the manufacturer’s curing time before painting or exposure
What affects drying
Thickness has the biggest effect: thicker coats hold more water. Ventilation, temperature and humidity come next. A well-ventilated room in mild weather dries quickly; a cold, closed room in winter can take far longer.
Avoid forcing plaster dry with high heat or dehumidifiers set too aggressively, particularly in the first 24 hours, as this can cause cracking and poor bonding.
How to tell when it is dry
Fresh gypsum plaster starts dark brown or pink and lightens to an even pale pink as it dries. Any darker patches — often in corners or where the coat is thicker — mean that area is still drying.
Decorating new plaster
Once dry, apply a mist coat of diluted water-based emulsion so the paint can soak in and bond. Avoid vinyl or oil-based paints as a first coat on new plaster, and use breathable paints on lime.
