Painting New Plaster / bare plaster – the ‘mist coat’
Here are the steps to follow when mist-coating new or bare plaster:
Make sure the plaster is completely dry
If you apply paint to plaster that is still drying out, then there is a risk that it will peel off as the plaster dries. When the plaster is a uniform, pale colour then it has dried out and is ready to paint – the drying time varies according to the thickness of the plaster and the temperature of the room, but typically takes 3-6 days for a well heated room but particularly deep areas can take longer to dry.
Choosing the Paint
The best paint to use is a 'contract matt emulsion'. There are a couple of reasons why. Firstly, it’s cheaper than standard ‘vinyl matt’ emulsion, and given that you are just using it as a first coat, there is no need to spend lots of money on an expensive brand. Secondly, ‘contract matt’ paint has less vinyl in it. This makes it less flexible and as a result, less likely to peel because instead of it forming a skin on top of the plaster, it will soak in properly.
Thinning the paint with water (The Mist Coat)
It is extremely important to dilute the paint with water because otherwise it will not soak into the plaster properly and may peel at a later date. If you don’t thin the paint then the water content in the emulsion will immediately be sucked out of the paint and this will also make it harder to apply and result in a poor finish.
How much water to add?
I tend to add 50% water (so a ratio of 1:1 paint/water). If I’m painting a bathroom I might add more like 60% water to be on the safe side as these types of rooms are particularly prone to peeling because of the steam that is produced by baths and showers.
Make sure that flooring and furniture is well protected
The mist coat is more likely to drip / spray from the roller because the paint is quite runny. As a result, you’ll need to make sure that you have covered up everything in the room properly.
How long does it take for a mist coat to dry?
The drying time for a mist coat various according to the temperature of the room but it is usually touch dry after 1 hour and ready to be re-coated after roughly 2 hours. Before applying the second coat, you’ll want to take some fine sandpaper and check to see if there are any rough areas. The mist coat will also show up any areas that need to be filled, so now is a good time to do that. After you have carried out filling and sanding, subsequent coats can be applied undiluted and depending of the colour, usually 2 or 3 additional coats are required.
Simmonds Decorating are painters and decorators based in Bath, Somerset, UK, who for 20 years have been serving both domestic and commercial customers in the local area. We carry out interior and exterior work and offer free no obligation quotes.