How Long Does Plaster Take to Dry Before You Can Paint?

Once the plasterer has packed up, it’s tempting to get the paint out straight away. But fresh plaster is full of water, and painting it too soon is one of the most common reasons new walls end up with peeling, bubbling or patchy paint. Here’s how long plaster usually takes to dry, how to tell when it’s ready, and how to paint it so the finish lasts.

The short answer

In a warm, well-ventilated room, a skim coat over plasterboard or sound existing plaster is usually dry enough to decorate in about a week, sometimes a little less. A full re-plaster, with a thick backing coat under the finish, holds far more water and can take several weeks. In a cold, damp room or in the middle of winter, everything takes longer.

Those are rough guides, not rules. The plaster itself will tell you when it’s ready.

How to tell when plaster is dry

Wet plaster is a dark pinkish brown. As it dries it turns a much lighter, even pale pink, so colour is the easiest check:

• Ready: the whole wall or ceiling is one even, light colour.
• Not ready: there are still darker patches, often in corners, around windows, behind radiators or near the floor, where the air doesn’t move as well.

If one area stays dark long after the rest has dried, keep an eye on it. It may just be a thicker patch of plaster, but damp that won’t go away can point to a leak or another moisture problem that needs sorting before you decorate.

What affects drying time

• Thickness. A skim is only a few millimetres thick. The backing plaster under a new finish is much thicker and holds much more water.
• What’s underneath. Plasterboard doesn’t hold much moisture, so a skim over new boards dries fairly quickly. Brick and block walls soak up water from a backing coat and give it back slowly.
• Warmth and airflow. Warm rooms with a steady flow of air dry fastest. Cold, closed-up rooms dry slowly.
• Time of year. Plaster put on in summer usually dries far quicker than plaster put on in a cold, damp winter.
• Other wet work. A new floor screed, lots of cooking and showering, or drying washing indoors all add moisture to the air and slow things down.

Can you speed it up?

A little, but gently does it. Open the windows when you can, keep internal doors open so air moves through the house, and keep the heating at a normal, comfortable level.

What you shouldn’t do is force it. A heater pointed straight at the wall, or the heating turned right up in a sealed room, dries the surface too fast, which can cause fine cracks and a weak, powdery surface. A dehumidifier can help in a damp room once the plaster has hardened, but avoid running one flat out in a closed room straight after plastering.

How to paint new plaster: the mist coat

New plaster is very absorbent. Roll ordinary paint straight on and the plaster pulls the water out of it before it can bond, so the paint can flake or peel later. The answer is a mist coat: a first coat of paint thinned with water so it soaks in and seals the surface.

• Use a basic matt emulsion, often sold as contract or trade matt, and thin it with water. The tin will usually say how much to add for new plaster.
• Don’t use vinyl, silk or wipeable paints for the first coat. They form a skin on top of the plaster instead of soaking in, which can lead to peeling.
• Some paints are made for bare plaster and don’t need thinning. If you use one of those, follow the instructions on the tin.
• Let the mist coat dry, then apply your top coats as normal. Two top coats usually give an even finish.

Wallpapering new plaster

Wait until the plaster is fully dry, just as you would for paint. Then size the walls with diluted wallpaper paste, or use a primer made for the job, so the paper can be slid into position and doesn’t grab the absorbent surface too quickly.

Common mistakes to avoid

• Painting while there are still dark patches.
• Using vinyl or silk paint for the first coat.
• Sanding a good plaster finish hard when it only needs the odd bit knocking off.
• Drying the room out too quickly with heaters.

Need walls or ceilings plastered?

Four Four Finishes skims and re-plasters walls and ceilings in homes across Poole, Bournemouth and the rest of Dorset. When we finish, we’ll let you know roughly how long the plaster needs to dry and how to prepare it for decorating. See our plastering services, or read our guide to skimming vs re-plastering if you’re not sure what your walls need.

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