Painting straight onto new plaster is a disaster waiting to happen. However, there are a few simple steps you can take to make sure you’re not left with hours of unwanted work just to get your newly plastered wall back to a workable surface.
The new plaster must be completely dry before any type of paint touches the surface. If it's not, it will lead to issues further down the line. And before painting a room, you need to apply what is known as a mist coat to ensure a smooth finish. Here, you’ll find what you need to know for success.
With The Paint Shed having evolved from painting contractors to retailers, Michael has years of experience within the painting industry, using this expertise to influence his own DIY projects using the best possible tools and materials.
Nick began his time with Harris in 1988, and throughout the decades has worked in various departments. His experience and product understanding informs the evolution of all Harris products, from benchmarking to insight, research and development.
1. Ensure new plaster is completely dry
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Before painting new plaster, it needs to dry properly, but it's not a quick-drying material. Michael Rolland, MD and paint expert at The Paint Shed, shares the minimum time that it takes: “A freshly plastered wall should be left to dry for at least a week.” He adds, “It may need longer depending on how well ventilated the room is.”
Article continues belowIf unsure, it should be left for longer, anything up to four weeks. Nick Parsons, Technical Manager at Harris, shares the signs that it is dry: “The plaster should turn from a dark, patchy brown to a uniform, pale pink.”
He adds why you shouldn’t paint before the plaster is completely dry, “It's very important not to rush this as painting before it's dry could cause the paint to flake, peel or even become mouldy."If you paint too early, the moisture gets trapped, leading to peeling paint or bubbly ‘efflorescence’, salty white spots.”
He adds, “Ensure the room is well-ventilated but avoid blasting the heating, which can cause the plaster to crack.”
2. Best mist coat ratio
New plaster is very permeable, which means it will absorb liquids, such as paint. To prevent this, a mist coat needs to be applied. Rolland shares why, "A mist coat will allow a more even paint texture on a freshly plastered wall.” He adds, “The best paint to use to achieve this is emulsion, as it is already water-based.”
Parsons shares, “A mist coat is just watered-down matt emulsion.” The ratios can vary, Rolland suggests, “One part water to ten parts paint.” But this can easily be “70% paint to 30% water,” shares Parsons. The ratio you use will depend on how thick the paint is to start with. It's better to be too thin than too thick.
He adds, “Use a non-vinyl matt emulsion as vinyl-based paints can create a skin that doesn’t bond properly to the fresh plaster.”
It's worth noting that many standard white emulsions will include information about the best ratio for using them as a mist coat on the product packaging. So if you're unsure if your paint is thick or thin, consult this before mixing your mist coat.
Shop these tools and paint to paint new plaster
A water-based emulsion ideal for mixing as a mist coat and as a top coat. Covers 16 m2 and has minimal VOCs, making it more eco-friendly.
A quality roller set with a 9" frame, 4 x 9" medium pile roller sleeves and a 9" tray. The roller sleeves have a medium pile nap, making them ideal for applying a mist coat.
A 3-inch synthetic paint brush ideal for cutting in on plaster walls. Its slimline head gives great control with sharp paint edges and no bristle splaying.
3. Painting new plaster
Step one: Prepare the new plaster
Before you start painting, make sure the plaster is completely dry and smooth. Use sandpaper - or a sander - to get rid of any imperfections. Use a fine-grit sandpaper, grade 120-220; is a good choice.
Prep the area by laying down dust sheets. Make sure to cover skirting boards with painter's tape to stop paint splatters and paint mist. Move or cover any furniture. Adding a mist coat can get messy.
Step two: Mix your mist coat
Matt white emulsion is the best choice for a mist coat. It's cheap and works with all colours. But you can use a coloured emulsion that is closer to the top coat for a better match.
To mix the mist coat, get a clean bucket and pour in the emulsion. Use a measuring jug for accuracy and don't go past halfway. Now, add the right amount of water and mix together. Use a mixing paddle (like this Helix Plus Mixing Paddle from Amazon) to get an even mix.
Step three: Apply your mist coat
The quickest option is a roller. This will be more messy than a brush but gives a good even finish. You can use a paint sprayer, but unless you are a pro stick with the brush and roller.
Start in a top corner with a brush — the best paint brush for the job will be a 4-inch one. Paint along the top of the wall to the opposite corner. Now go along all the edges before getting out a paint tray and a roller.
The best paint roller for painting new plaster is 9-inch roller. Pour the mist coat into the paint tray and coat the roller with paint, but don't overload. Using a smooth even motion start at the bottom and roll to the top until the wall is covered. Don’t roll over the same spot too often.
Once finished, leave to dry for 24 hours, check there are no damp spots. Once completely dry apply the top coat — typically you will need two.
FAQ
How many mist costs are needed?
“Usually, one thorough mist coat is enough to seal the surface,” shares Parsons. However, this can differ depending on the paint and mist coat ratio used. Rolland says, “If the wall seems to have absorbed a lot of it, or if it looks patchy, a second coat can be a good idea.”
Parson shares, “You’ll know it’s worked if the paint applies like it would on a normal wall. It usually dries very fast - often within 1 to 2 hours - because the wall absorbs the moisture so quickly.” Once the paint is dry, add two top coats of your preferred paint.
To get the job done quicker and with less mess, Parsons says, “To save time and reduce spatter, use a roller with a wider core - like the Harris Powercoat Roller from Amazon.” He adds, “It holds more paints meaning fewer trips to the tray and gives much faster coverage on large walls.”
As soon as your mist coat is dry, get some expert insight on how to paint a wall with a roller and how to clean paint rollers to keep them in tip-top condition, ready for your next paint project.
