Pro Tips - How To Mist Coat New Plaster
Many people ask us "can I paint straight on to fresh plaster?" the simple answer is "No", however this is not a dark art or a hidden mystery known only to professional painters and decorators. In this simple guide we hope to answer all of the usual questions and give you a step by step guide to creating a professional finished room starting from new plaster.
How long does plaster take to dry before painting?
New plaster can take anywhere between two and five weeks to dry, this all depends on ambient temperature and ventilation. We try to advise people to not focus on time but look more at the colour and moisture content of the new plastered surfaces. A professional decorator will use a damp tester and is looking for a reading no higher than 12% moisture content. If you are a DIY enthusiast and you're unsure there is a visual test, if the plaster has gone a very even pale pink colour with no darker patches to corners, edges or flooring then you're pretty much ready to go (see image below). Avoid painting to early as the plaster will still let its moisture out and this will cause new paint to flake and peel.
What is mist coat painting new or fresh plaster?
Most unpainted new surfaces require a primer, a mist coat is simply a primer for newly plastered surfaces. Plaster is very unique, when dry it is like a sponge that is very absorbent, so much so that any normal paint applied to fresh plaster will dry too quickly leaving the pigments (colouring) not adhered to the surface, the end result is peeling and flaking paint every time. To slow down the drying process allowing the paint to penetrate and adhere to the porous plaster a mist coat is required. A mist coat is simply a water diluted emulsion paint which has long been the tried and tested method of priming (mist coating) new plaster.
What is the ratio of paint to water for new plaster?
Firstly, choose your paint, "what is the best paint for mist coat on new plaster?" we recommend a Contract Matt, all key paint brands have one within their range and oddly enough it's often the cheapest product they produce. We then advise a dilution ratio of 40%, so if you buy a 10 litre tub simply mix with 4 litres of water. As a general rule we apply mist coats will a roller (unless its a large project then we will use Airless Paint Praying), it's sloppy and messy so make sure everything is well covered. Pro Tip - when applying a mist coat it often looks very thin and you can be tempted to add more and more, be patient as mist coat dries it becomes more opaque and a stronger white slowly reveals itself during the drying process.
A before and after video of new plaster (press play)
How soon can I paint after a mist coat?
Leave a mist coat at least 24 hours before painting, if the ambient temperature is cool and ventilation is poor then be safe and leave it 48 hours. We recommend at least two top coats to get the depth of colour required on top of a mist coat.