As I mentioned, adding water to the first coat helps the plaster to really bond to the paint as it's able to soak it up due to the paint being thinner.
Hi,yes,all new plaster work,when fully dry, requires a mist coat(a thinned down coat of emulsion) Most paints will say on the tub that they need watering down by at least 10% with clean water for use on new plaster.
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.
Next the plaster is going to need a sealer coat applied, as new plaster is very porous. The traditional method of doing this is to thin out your 1st coat of emulsion by about 30 to 40% with clean water, making a sealer coat. This will penetrate deeply into the surface stopping any flaking off later on in years to come.
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.
Without the mist coat you're likely to have very poor adhesion between your paint and your plaster and quite often it will crack, flake or even peel off in sheets in some instances!
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.
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.
Mix your mist coat paint
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.
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.
When a painting contractor waters down paint, they are typically adding a significant amount of water to it. Think two gallons of water for every five gallons of paint. In contrast, the process of thinning paint involves a relatively small amount of water: 2-4 cups for every five gallons of paint.
Oil-based paints should be thinned or cleaned up only with petroleum or mineral-based products. In contrast, latex paint is water-based and should be cleaned up and thinned only with water.
What ratio should a mist coat be? When I mix mix coats using Auro 555 natural wall primer, I mix 1 part water to 9 parts paint, so 10% water to 90% paint. This can vary with the paint, but anywhere between 10-20% will be the best ratio for your mist coat.
First and foremost, let the plaster dry. Paint won't adhere properly to wet plaster, so make sure it's fully dried. This takes around 3-5 days for overskim or 4-6 weeks for a new plaster wall, though it can take longer depending on humidity and ventilation.
It can make water-based emulsion paint easier to work with as it flows more smoothly. And, against what you might think, it can cover a lot better. In terms of how much water you need, remember you can add but you can't take away. Generally, around 200ml is perfect for a 5 litre tin of paint.
Fresco is a mural painting technique that involves painting with water-based paint directly onto wet plaster so that the paint becomes an integral part of the plaster.
This is essentially just a watered-down emulsion that soaks into the plaster to create a bond that will then allow your paint to stick properly.
Paint with a smooth motion to give even coverage across the wall. You'll usually only need to apply one mist coat, but you can apply a second if you don't feel you've properly sealed the plaster. If you're using a primer, always follow the instructions on the packaging.
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.
It should be thin enough to absorb into the plaster but not so watery that it needs colour and coverage. Test the mixture: if possible, test it on a small, inconspicuous plaster area to check its absorption and drying. Mixing a mist coat is a straightforward but essential process in painting new plaster.
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.
Bare absorbent surfaces such as new plaster can be sealed using Armstead Soft Sheen diluted with 1 part water to 20 parts paint to mist coat the surface.
When painting highly absorbent surfaces like fresh plaster, bricks, or concrete, thinning the first coat is crucial: Mist Coat: Create a “mist coat” by mixing the first coat of paint with 50% water.
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.
Painting a newly plastered wall requires more preparation than painting a normal wall. You can't start painting new plaster directly and instead have to take steps to seal the plaster so you can get the colourful finish you want.