What Causes It? Peeling from plaster could be a result of insufficient wet troweling of the white coat when the plaster was originally applied, causing chalking of the surface.
I would suggest sanding then coating with watered down PVA glue in order to achieve a seal over surface. Also would recommend this in the first instance on newly finished plaster to prevent flaking/peeling or cracking.
Let the plaster dry
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.
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.
This usually happens when a mist coat is either not present or insufficient. The fresh plaster just sucks all of the moisture out of the paint and leaves the dry paint to flake off.
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.
Moisture. One of the main causes of peeling paint is the presence of moisture or water around the paint. This will usually happen when water gets into the wood behind the paint. This separates it from the wall and seeps through the layer of paint.
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.
1 Pottery Plaster mixed to a consistency of 70 (70 parts plaster to 100 parts water) recommended for most studio applications. Excessive water yields a more porous but more brittle mold, and less water means a very dense, hard mold that will not absorb water.
Make sure the plaster has been left to dry for a few weeks before you begin painting. There is one type of paint that can be used on plastered walls before the drying time has passed. Contract matt paint is designed for use on damp plaster. It is permeable, allowing the plaster to breathe through a single coat.
What Causes It? Peeling from plaster could be a result of insufficient wet troweling of the white coat when the plaster was originally applied, causing chalking of the surface. Very hard plaster may be slick, reducing the adhesion of any coating.
Light sand and brush
Freshly-plastered walls should be smooth on the whole but you may find the odd plaster splash or pieces of dust that have been left. Use a fine sandpaper and a brush to remove these blemishes but don't be too vigorous with your sanding.
Over time, as the painted surface ages, it will become less flexible and less capable of withstanding the stress and constant movement (expansion and contraction) in the substrate. The destructive result is loss of adhesion through crazing, cracking, flaking, peeling or blistering of the paint system.
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.
Remove all loose and flaking paint with a scraper or wire brush, sand the surface and feather the edges. If the flaking occurs in multiple layers of paint, use of filler may be necessary. Prime bare timber areas before repainting. Use of a premium quality primer and topcoat should prevent a recurrence of the problem.
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.
Subtle Discoloration
Often with a slightly brown or yellow hue, this discoloration can be noted on both plaster and any wall coverings placed over affected plaster, such as wallpaper or fabric. Subtle discoloration may also be accompanied by a faint musty smell, indicating moisture that hasn't fully dried.
Top tip: If you don't let the plaster dry and apply emulsion paint to wet plaster, it's likely to crack and peel off. Painting new plaster that's completely dry can also leave you with uneven brush strokes.
For gypsum plaster, we generally recommend waiting around 24 hours between coats. This period allows the plaster to harden and set properly, providing a sturdy base for the next layer.
Fresh plaster is porous and will therefore absorb moisture. If you attempt to paint over plaster that is still damp the paint is likely to peel off. This is obviously not ideal! We really recommend holding yourself back and waiting before painting your new plaster.
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!
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.
To understand why paint is peeling off your plastered walls, you need to know one or two things about plaster. In summary, if you've not allowed the plaster to fully dry and/or you've not primed the dry plaster properly before painting, your wall paint will peel and flake.
Yes, with proper preparation, priming, and painting, peeling paint can be restored effectively.
Peeling or Bubbling Paint
Example of peeling and bubbling paint caused by humidity damage. If your paint is peeling or bubbling, also known as paint blistering, there's likely excessive moisture in your home that's causing the paint to lose surface adhesion.