Painting new plaster? Here’s how to apply a mist coat

Before starting, it’s worth knowing that getting to the décor finish line with a freshly plastered wall is a little trickier than painting an ordinary wall. It’s best to approach this task with a bit more patience and caution.  

But don’t worry, your Exceptional Homes Team is here to share top tips for mixing and applying an ideal mist coat, with some professional pointers from trusted painting professional Artur Soszynski of Prime Projects, London. 

Soszynski is a decorating expert who has been working on interiors for 20 years and specialises in bespoke and non-standard finishes including limewash, structural paints, Venetian stucco, etc. One of his latest painting projects featured on NBC’s Open House. 

Soszynski suggests that a sprayer may be used instead of a paint brush or roller, though you will need to be confident using the tool. Soszynski uses a Graco GX21 Airless Sprayer. For this task, paint sprayers are best left to professionals who have lots of experience with this tool, so only use if you are very confident in your sprayer skills. 

A mist coat is a layer of watered-down matt emulsion paint which is applied first, and directly, to dry plaster. Fresh plaster is highly absorptive. If you applied your favourite topcoat paint directly to a freshly plastered wall that hasn’t had a mist coat, the paint would dry very quickly. Your wall would be covered with irregular brush strokes and have an uneven finish. Eventually the paint would peel and chip off the wall.  

Mist coat paint seals your plastered wall. It gives the bone-dry plastered wall something to absorb so that your topcoat paint can stick to the surface. 

Your fresh plaster will need to be completely dry before adding your mist coat – this will be a minimum of a week and can be up to two weeks. To slightly speed up drying, you can try using a heater or keeping your window open. When plaster is fully dried it won’t have any dark patches and will have a consistent colour. If paint is added to plaster that isn’t completely dry, the surface may develop damp from the moisture trapped in the plaster.

For the novice mist coat painter, there are typically two options for applying your mist coat – you can use a brush or a paint roller. The roller will be quicker and gives a more even finish, but due to the runny consistency of the mixture you might find the task to be messy. A paint brush cuts down on the mess but the process of painting your wall will take more time. 

A standard paint job is messy. Applying paint mixed with water? This calls for tactical thinking around protecting your furniture and décor. While you are waiting for the plaster to dry, you can leisurely put down dust sheets to protect your floors and to tape up any surfaces where necessary. 

You also need to protect yourself. At the very least, wear old clothes you don’t mind getting splattered with paint, and make sure your arms and legs are covered. Wear safety goggles to keep the mixture out of your eyes.

To achieve a professional paint finish, go over your dry plastered wall very gently with a scrapper to remove any excess plaster. 

Once done, run your hand over your plastered wall lightly. You’re checking that there are no imperfections or bumps. The good news is that if any imperfections have slipped through your initial inspection, the mist coat will reveal these before you apply your topcoat. 

No one on the internet can seem to agree on the ultimate mist coat mix, and that’s because each paint is formulated differently. 

Some paint manufacturers helpfully give guidance for ratios needed for using their brand of matt emulsion for mixing your mist coat.  

If the brand you prefer does not have this information, a good rule of thumb is for thicker (and usually more expensive, for example, Little Greene) paints, the ideal mist coat ratio is 50/50 – 50% paint to 50% water. For , thinner matt emulsion paints (for example, Dulux), try a mist coat ratio of 70/30 – 70% paint mixed with 30% water. 

Depending on what the top–coat paint brand will be, Soszynski creates a mist coat using that same brand of paint. He suggests that Armstead or Leyland paints work well, and typically uses a 50/50 mist coat ratio. 

Give your matt emulsion paint a stir using the stick or stirrer for 20-30 seconds 

• Pour the stirred matt emulsion paint into a bucket 
• Add the appropriate amount of water to achieve the desired consistency (e.g. 50/50 paint-to-water ratio or 70/30 paint-to-water ratio) 
• Use your stick to stir the mixture (you may also find it helpful to use a paint mixer on a drill if you have this tool to hand). You’ll know your mist coat is properly mixed if there’s no water settling on the surface of the emulsion 
• Your mist coat mix should be runny but should still stick to a paintbrush. Adjust with paint or water until you get the appropriate consistency 

• Pour some of the mist coat mixture into the roller tray 
• Dip your brush in the mist coat and, starting at a top corner, paint along the top of the wall and along the wall’s edges 
• Carefully roll the roller brush (or dip the paint brush) into the mixture in the roller tray – drag along the flat part of the tray to remove excess
• Starting at the corner of your wall, roll or paint the mixture on the wall in sections, being sure to keep the coverage thin – this will ensure you end up with a smooth finish 

• Go over each section with the roller or paint brush a few times to ensure you don’t get bubbles and drips 
• When finished, the surface will look thin and patchy, but when the mist coat dries you will end up with a bright white finish 
• Once you have finished adding your mist coat to the entire wall, dip your corner roller into the paint and run it along the corners of the wall – this will avoid leaving any marks from the bigger roller or paint brush in the corners (optional) 

Let the mist coat paint dry for 2-3 hours. Check there are no damp spots before applying at least two topcoats of your final paint colour.  

If you feel that you would like to give mixing your own mist coat a miss, you can always opt to use ready-made products. 

Soszynski recommends Tikkurila Optiva Primer or No Nonsense Trade Bare Plaster.