Skipping the mist coat on fresh plaster can lead to issues such as uneven paint absorption, poor adhesion of subsequent paint layers, and a less durable finish. The mist coat acts as a primer, sealing the plaster and providing a suitable surface for the final coats of paint.
Really it's not an option not to do a mist coat as the consequences are quite the disaster! 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!
Alternatively, you can use a water-based primer which saves you the mess of making a mist coat. All our primers are water-based and will help you achieve an even and colourful finish. To make a mist coat, mix three parts emulsion with one part water.
A mist coat should be left to dry for around 24 hours, even if it feels dry before this. Only one mist coat should be needed, but if you have some paint leftover that's already been watered down, you might want to add a second mist coat. As long as the first coat was dry, two mist coats will do no harm.
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.
What happens if the mist coat is too thick? If the mist coat is too thick, it won't absorb into the plaster properly, which can lead to issues with adhesion.
Typically, wait at least 24 hours before painting after applying a mist coat. Ensure it's fully dry to achieve the best results.
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.
To make your mist coat grab a standard emulsion paint and water it down by around 20-30%. Apply one or two coats of this to your wall. If you are unsure of how to mix a mist coat or don't have any paint lying around for the job we do have Optiva Primer which is perfect for the job.
A mist coat needs to be absorbed by new plaster so it needs to be pretty thin, almost like a thin soup. If it's not thin enough it won't do its job properly. Use a white emulsion (it doesn't need to be high quality) as this provides a good base colour for any top coat.
On bare plasterboard or plasterwork, the first coat of paint should be what is called a 'mist coat' and this should always be a matt or vinyl matt emulsion paint. Never use vinyl silk paint for a mist coat.
Mist coat paint is simply watered-down emulsion paint, which acts as a primer. All you need to do is get some white emulsion paint and thin it out with water. Three parts paint to one part water should do the trick. As an alternative to watering down your paint, you can also use Dulux Sealer for Plaster.
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.
Once your plaster is dry you may need to lightly sand the surface – although this shouldn't be necessary if you're plasterer is a good one! Use a nice fine sandpaper of around 200-400 grit for a smooth finish. After a sanding, it's time for a mist coat to seal in the plaster…
The plaster must be completely dry and free of dust and flaking before getting started. Next, a 'mist' coat of paint needs to be applied. 'Mist' paint is a watered-down cheaper emulsion paint in a similar colour to the topcoat which, once applied, should be absorbed into the fresh plaster.
What Does Dry Plaster Look Like? Dry plaster achieves a pale pink color once it is completely dried off. Depending on the mixture and ingredients, it will initially have a dark pink color. Once it is dried, all brown patches disappear, and a regular, uniform pale pink color will be achieved.
Primer helps create a smooth and even surface, improves paint adhesion, and enhances the durability of the paint job. It also helps prevent issues like rust. Skipping the primer may result in an uneven finish and reduced paint longevity.
Why Mist Coat? We always recommend applying a mist coat because skipping this step can lead to quite disastrous consequences. For example, painting directly onto plaster can cause paint to flake, crack and more.
Applying a mist coat can be messy, so it's a good idea to protect the floors and any furniture that remains in the room with dust sheets. You can apply a mist coat with a roller or a paintbrush. A roller will be quicker but will create more mess than if you use a paintbrush.
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.
To properly sand between paint coats: Start with a fine-grit sandpaper, sand in a circular motion, clean the surface thoroughly, and apply the next coat of paint. Cleaning up dust is important to prevent it from interfering with the next coat of paint. Use a tack cloth or vacuum to remove dust particles.
You only need one layer of mist coat before applying your normal emulsion, which should be applied in 2-3 layers. In terms of the mist coat drying time, you should leave the mist coat for 24 hours to allow it to set perfectly.
Consequences: Applying a second coat too soon can lead to peeling, streaking, and uneven colour distribution. Solution: Always follow the recommended recoat times and test a small area if you're unsure.
You have to be really careful before introducing a dehumidifier to your newly plastered home. Take out too much humidity, and the plaster will dry too quickly, causing hairline cracks and brittleness over time. Plaster needs a humidity of around 60-70% to dry properly, while still staying hydrated enough to dry evenly.
Weathered Surfaces: If the existing paint is weathered, faded, or peeling, applying two coats is generally recommended to ensure proper coverage, adhesion, and protection against moisture and UV damage.