Painting New Plaster: Drying Times and the Mist Coat

How long before painting new plaster

New plaster has to be fully dry before you paint it. Plaster on plasterboard needs 2 to 3 days to dry and backing plaster needs 4 to 6 days, and it can be wise to wait at least a week. Dark patches mean the plaster is still damp, so leave it alone while you can see any.

The waiting does not end when the plaster is dry, because the mist coat and each topcoat need their own drying time.

Surface or coat	How long to wait
Plaster on plasterboard	2 to 3 days before any paint
Backing plaster	4 to 6 days before any paint
Any new plaster, to be safe	At least a week
Mist coat	Until it has completely dried, which can take up to 24 hours, especially in a humid room such as a bathroom
Each topcoat	Overnight before the next coat
Plaster that pulled away under the roller	At least 24 hours before you repair it

Why new plaster needs a mist coat

New plaster is porous. Without a first mist coat it absorbs the water in the topcoat, and the topcoat can blister and peel. A mist coat is paint thinned with water, and it goes on before any topcoat.

Indoors, paint also blisters and flakes when moisture or dirt is trapped under it. Cracks that appear in the paint, particularly in new homes, are the plaster cracking underneath, and the fix is to fill, sand and repaint.

Mist coat ratio for new plaster

A typical mist coat is three parts water to one part paint, though the mix can vary with the paint you use. Choose a non-vinyl water-based paint, so the plaster can breathe and moisture can escape.

A mist coat can take up to 24 hours to dry, especially in a humid room such as a bathroom. Do not put the next coat on until the mist coat has completely dried.

How many coats new plaster needs

After the mist coat, two topcoats will most likely be needed, each left to dry overnight. A darker colour going over a white mist coat can need more than two, but very rarely more than three.

Some emulsions made for new plaster work better with the first coat watered down slightly, at one part water to three parts paint. That coat is mostly paint while a mist coat is mostly water, so do not use one mix in place of the other.

How to paint new plaster, step by step

Once the plaster is dry, sand off any rough edges with high-grit sandpaper such as P180 and wipe the dust off with a damp cloth. A roller with a 3/8-inch or 1/2-inch nap suits new plaster, and each section you roll should be no larger than 2 square metres. Work through the steps in this order, letting each coat dry before the next goes on.

Painting a new plaster ceiling

A newly plastered ceiling goes through the same drying time, mist coat and topcoats as a wall. Boarding over an Artex ceiling and plastering it, or sealing the Artex with PVA and plastering straight over it, also leaves new plaster on the ceiling to paint this way.

Getting a decorator to paint new plaster

Repairing small water-damaged areas of plaster typically costs £50 to £100 on Checkatrade’s figures, and for a larger plastering job you hire a plasterer, whose day rate is typically around £300.

Among the Nottingham decorators compared on the guarantees they put in writing, ARD Decor in Rise Park guarantees its workmanship and provides a warranty on all jobs, and all ten firms on the list give free quotes.

When you ask for a quote, say when the plaster went on, whether it is on plasterboard or backing plaster, and what colour is going over it. Those decide how long the decorator waits before painting and how many topcoats the job needs.