How long does plaster take to dry before you can paint?

Plaster dries in days or weeks, never hours. A skim over plasterboard is usually ready to paint in 3 to 5 days in a warm, aired room, while a wall hacked back to brick and replastered needs 4 to 6 weeks. We give drying times by plaster type and by job, how to tell a wall is dry, how to speed it up without cracking it, and when to mist coat and paint.

Plaster drying times by type

The drying time is set by how much water went onto the wall. A thin finishing skim holds little and dries in days. A thick backing coat on brick holds far more and takes weeks. The times below run until the plaster is dry enough to decorate, in a room kept at around 18 to 22°C with some fresh air.

Skim coats

A skim is the thin finishing coat. Over new plasterboard it firms up in the first 24 to 48 hours and is ready for a mist coat in 3 to 5 days. Over an existing wall, allow 3 to 7 days. The surface underneath is one of the things that sets the pace, and old walls vary far more than new board.

Backing coats and full replastering

Bonding, hardwall and browning are backing plasters. They go on thicker, to straighten an uneven wall before the skim, so they carry more water and take 7 to 14 days to dry. Browning sits at the slow end, at 10 to 14 days, and one-coat plaster, laid thick enough to be the finish too, takes 14 to 21.

A wall hacked back to the brick and replastered gets a backing coat and a skim, and needs 4 to 6 weeks before paint. That is the gap to leave after a full replaster, even though the surface looks pale much sooner. Dry on the surface is not the same as dry right through.

Lime plaster

Lime plaster is the slowest of the common plasters, at 4 weeks or more before decorating. On an older house plastered in lime, plan the decorating for a month after the plasterer leaves at the earliest, and longer in winter.

Drying time for a room, a ceiling or a whole house

Plastering is booked by the room, so this is the table most people plan from. It gives the plasterer's time on site, then the drying time before a decorator can start, for a warm, ventilated house.

A room can be skimmed in a day, but the drying adds most of a week. Board and skim takes longer on both counts: 1.5 to 2 days on site and 4 to 5 days of drying for an average room. A whole house needs 1 to 2 weeks of drying after the last room is done.

Ceilings

A ceiling dries at the same rate as a wall with the same plaster on the same background, so a skimmed plasterboard ceiling follows the board row: 3 to 5 days. It is harder to judge from below. Check it in daylight with the lights off, and look hardest along the outside wall, which stays coldest.

Bathrooms

Bathroom plaster dries on the same clock as any other room, as long as nobody showers in it. Each shower puts water back into the air the walls are trying to dry into. Keep the shower out of use until the walls are dry and sealed if you can. If you cannot, run the extractor fan for an hour after every shower.

How to tell plaster is dry

Watch the colour. Wet plaster is a dark, damp brown-pink. As the water leaves, it lightens to an even pale pink, beige or peach, and a wall is dry when that change has reached every part of it.

Dark patches are wet patches, however ready the rest of the wall looks. Check the corners, the window reveals and the wall behind radiators and furniture, where the air moves least.

A moisture meter settles it where the colour is hard to read, such as on a ceiling or a wall in poor light. Readings differ from one meter to the next, so compare the new plaster against an old, dry wall in the same house rather than against a number.

What slows plaster drying

After the type of plaster, four things set the pace: the temperature of the room, the humidity of its air, whether that air goes anywhere, and how thick the plaster is.

• Temperature. The drying times above assume a room at around 18 to 22°C. A cold room slows every one of them, and in winter plaster takes 50 to 100% longer to dry.
• Humidity. Humid air can double the drying time. Aim for 50 to 60% relative humidity and no higher, because above 60% mould can start to grow on surfaces that stay damp.
• Airflow. Water leaving the wall has to leave the room too, or it settles as condensation on the windows and in the coldest corners. A sealed room keeps the moisture next to the plaster.
• Thickness. Every extra millimetre of plaster is more water to lose, which is why a backing coat takes twice as long as a skim, or longer.

Season is the one you can plan around. A skim that dries in 4 days in a warm room can take 6 to 8 days in a cold house in January. November to February is also when plasterers' rates run 10 to 20% lower, so a winter booking trades a lower price for a longer wait before painting.

How to make plaster dry faster

Plaster dries faster with gentle, steady warmth and moving air. High heat aimed at the wall does not help. It can crack the plaster and leave it weaker.

• Keep the heating low and steady. Leave it on low day and night, rather than off overnight and high in the day, so the room never drops cold.
• Let the damp air out. Open a window slightly or leave the trickle vents open, and keep the door to the rest of the house shut so the moisture goes outside, not into the hall.
• Keep the air moving. A fan moving air around the room helps, as long as it does not set up a strong draught across the new wall.
• Use a dehumidifier in a cold or humid room. Set it to hold the room under 60%, and shut the window while it runs, because it can only dry the air it has. A refrigerant model suits a heated room, and a desiccant model suits a cold one, such as an extension with no heating yet.

Pick a dehumidifier that removes at least 5 litres of water every 24 hours. A decent one starts at around £100, which is less than a single day of a plasterer's or a decorator's time.

Will plaster crack if it dries too fast?

It can. Plaster forced dry with a heater, a hot air gun or strong sun through glass can crack and end up weaker than plaster left to dry at room temperature. Fine surface cracks that show anyway are filled and sanded before the mist coat, and a crack that keeps reopening is worth showing to the plasterer.

When to paint new plaster

Paint when the whole wall has turned pale and the drying time for its plaster has passed. The first coat is always a mist coat: emulsion thinned with water, never a standard coat straight from the tin. Bare plaster soaks paint up like a sponge, and the thinned coat seals it so the top coats stick.

Dulux puts complete drying at up to 4 weeks as a rule of thumb, and suggests a mist coat of ten parts white emulsion to one part water. Plasterers often mix far thinner, down to 60% paint and 40% water. Follow the instruction on the tin you actually buy.

If you would rather not mix it, a sealer made for plaster or a bare plaster paint does the same job straight from the tin, and a bare plaster paint can be recoated after about 4 hours. Once the first coat is dry, the top coats follow, and bare plaster often takes a third coat before the colour looks even.

If you are booking a decorator, give them the day the plasterer finished and what went on each wall, and set the start date at the far end of the drying range. A decorator who arrives to damp walls either loses the day or paints them anyway.

A drying timeline for a skimmed bedroom

A skim is a day's work for one room: an average bedroom takes 6 to 8 hours, and a plasterer charges £450 to £680 for it. From there, a warm house with the heating on runs like this.

1. Day 1. The room is skimmed. The heating goes on low, a window stays slightly open, and nothing touches the walls.
2. Days 2 and 3. The skim firms up in the first 24 to 48 hours, then the walls start to lighten. No filler, no sanding and no colour samples yet.
3. Day 4 or 5. With 3 to 4 days of drying behind it and the colour even all over, the mist coat goes on.
4. Day 5 or 6. The first top coat goes on once the mist coat is dry, and the second follows it.
5. In winter. Drying takes 50 to 100% longer, so the mist coat moves to around day 6 to 9.

In a whole-house job the drying days are not dead time. In the order of works in a renovation, second fix follows plastering, so sockets, switches and the kitchen go in while the walls dry, and the decorator comes in after.

What happens if you paint plaster too early

Paint on damp plaster traps the water behind it. Emulsion rolled onto wet plaster is likely to crack and peel, and the finish flakes as the wall keeps drying underneath.

The fix is to scrape back the failed paint, let the wall dry for the time it should have had, then start again from a mist coat. The waiting you skipped comes back, plus a second round of decorating.