All you need to do is dilute some emulsion paint with water and apply it to the plaster using a roller, paintbrush or spraying. One mist coat should suffice, but you can apply a second (or even third) coat just for extra peace of mind. That way, you can rest easy knowing that the plaster is sealed.
Newly plastered walls need sealing in the same way as your ceiling or drywalls: they should have a stabilising primer layer first, before they're applied with at least two coats of paint. A previously painted wall should also have at least two coats, without the primer layer first.
It's perfectly fine to paint over new bare plaster. Firstly you will need to apply a mist coat (thinned down emulsion) this is a very important step, it needs to be able to sink into the absorbent plaster and needs to be thin and not leave a roller texture on the wall.
On new plaster, the first coat needs to penetrate the surface to bond. If the first coat is not watered down it will almost certainly be too thick to do this, so will not penetrate and just lay on the surface, which is a dusty surface. In time the paint will peel off leaving a horrible mess.
In good conditions – typically in summer months – this will usually take around three days. However, we'd recommend leaving it for at least two weeks if possible to be safe. In the wrong conditions, plaster can even be known to take up to four weeks to dry!
There are a wide range of reasons paint can peel, including the surface being damp, salt migrating through the plaster causing the paint to peel or the surface not being completely clean before painting.
The short answer is 1 mist coat. However, the consumer needs to also consider what brand of paint they are using & from where they purchase! As professionals, we use Trade quality paint which has more coverage than retail & own brand paint purchased in a Diy store. Also, think of the location of the area being painted.
Very hard plaster may be slick, reducing the adhesion of any coating. New plaster might have a high pH level, which will require a primer resistant to alkalinity. Old plaster that has become powdery. Poor surface preparation.
There are two methods to sealing the new plaster. Firstly, you can use a mist coat of white watered down emulsion. However, it is more preferable to use a primer or top coat and water down the first layer by 10%. This allows the initial coat to properly soak into the plaster aiding adhesion of the final coat.
Too Much Water
You don't want to be too thin, but a mist coat needs to be thin—almost like a soup. The water will not seep into the substrate if the mist coat is too watery.
Mist coat paint is simply watered-down emulsion paint, which acts as your primer. All you need to do is get some white emulsion paint and thin it out with water – it's that easy! Ten parts paint to one part water should work. If you don't fancy watering down your paint you can also use Dulux Sealer for Plaster.
While some may suggest plastering and painting on the same day, it's essential to allow the plaster to cure before applying paint. Waiting for the plaster to dry completely, typically for around two weeks, allows all moisture to evaporate. This helps prevent issues such as paint peeling in the future.
If you've hired a professional plasterer, probably not. It should be super smooth with a uniform finish. If you've plastered yourself, or if you can see a few spots and bumps (which could be a splash of PVA or plaster), you can lightly sand these back to avoid them showing up once you've painted.
As mist coat is of a watery consistency, it's perfectly normal for it to look patchy once it's dried down. But as it's only purpose is to seal the plaster and prep the surface ready for paint, a patchy finish is nothing to worry about.
Applying the second coat too early will result in lost time, money, and effort. Not only that but it'll also create additional stress that's not necessary. Applying the second coat too early will result in streaks, peeling paint, and uneven color.
One of our easy, Harris-approved tips for painting new plaster that helps to overcome this issue is using a watered-down first layer of paint called a mist coat. This mist coat helps the plaster to absorb the paint superbly.
So watering down your first coat as a 'mist coat' will help the plaster to soak up the paint and create a bond between the new plaster and the paint. For new plaster it is critical that you start with a mist coat, which leads me quite nicely into my next section… what will happen if you don't mist coat!
Put simply, a mist coat is the first coat of paint that's put on bare plaster. Think of it as a base that's used to prime and seal the wall. Without the mist coat, the plaster will soak the moisture out of the paint like a sponge, causing it to crack as it dries.
Observe how the plaster behaves – if it sucks the primer in evenly then you can be sure this is will also happen when paint is applied, you may find you need 2 or 3 coats for full obliteration with white paint over the pink finish. For the best results leave 4-6 hours between coats for drying.
Three coats of paint can be a little much, but it will depend on the colour and quality of your paint. Cheap paint generally is thinner and will need more coats, so three may be the right amount.
The very first thing you need to do when painting new plaster is to let it dry. A week should be long enough to let it completely dry out and for all damp patches to disappear. Once the plaster is dry it should be light with no dark spots and a consistent colour and appearance throughout.
The main reason why paint cracks is due to poor preparation on fresh plaster. Fresh plaster needs to be totally dry prior to applying paint. It also needs to be primed before adding emulsion.
Patchy paint can result if paint has been applied unevenly. Patchy paint can be down to a variation in surface absorption. Walls might appear patchy if they have variation in texture. Using paint that is not fully mixed can cause a patchy appearance.
Always make your mist coat using a matt emulsion. If you use a vinyl-based paint, a skin will form on the plaster that will cause problems with peeling. Specialist paints such as Dulux Super Matt are a good choice to create a professional finish.