The short answer
A fresh skim coat usually takes 5 to 7 days to dry before it is ready to paint. Thicker work, such as a wall that needed a backing coat as well as a skim, can take two weeks or more. A cold, damp or closed-up room takes longer than a warm, airy one.
When we finish a job we tell you roughly how long that room needs and how to prime it, because the right answer depends on the wall, the room and the time of year.
What affects drying time
| Factor | What it does |
|---|---|
| Thickness | A skim is only a few millimetres thick and dries fastest. Backing coats and deeper repairs hold far more water. |
| What it's on | Plaster over plasterboard usually dries faster than plaster on solid brick or block, which holds moisture of its own. |
| Temperature | Plaster dries more slowly in winter. A room that stays cold overnight can add days. |
| Airflow | Moisture has to leave the room. Open windows and doors make a real difference. |
| Humidity | Kitchens, bathrooms and houses where other wet trades are working dry more slowly. |
How to tell when it is dry
- Colour. Wet plaster is a darker brown. As it dries it turns an even, light pink from edge to edge.
- Dark patches. Any darker areas are still wet. They usually linger in corners, behind radiators and around window reveals.
- Feel. A wall that feels cool or damp to the back of your hand needs longer.
Wait until the whole wall is one even, pale colour before you paint.
Helping it dry, and what to avoid
- Do keep the room ventilated and leave internal doors open.
- Do keep the heating on low in cold weather, so the room stays gently warm.
- Don't point heaters or fans straight at the wall, or blast it with a dehumidifier in the first few days. Plaster that dries too fast can crack or lose strength at the surface.
- Don't hang pictures, push furniture against the wall or put up shelves until it has dried.
Painting new plaster: the mist coat
New plaster is very absorbent, so the first coat needs to soak in and seal it. That first coat is called a mist coat: a matt emulsion thinned with water. Many paints give a mixing ratio for new plaster on the tin, so follow that. Some paints are made for bare plaster and need no thinning.
- Use a plain matt emulsion for the mist coat. Vinyl, silk and wipeable paints form a film that doesn't soak in, and can peel.
- Let the mist coat dry fully, then apply your finish coats as normal, usually two.
- For wallpaper, wait until the plaster is completely dry, then size the wall first so the paper can be slid into place.
Not sure if your wall is ready?
Send us a photo or give us a call and we'll tell you. If the plaster on a wall is cracked, blown or patchy, we can repair it or give it a fresh skim. Quotes and site visits are free.