Mist Coat Paint for Sealing Plaster

If you have recently been carrying out refurbishment work throughout your house you may have had areas that have been skimmed with some fresh new plaster. Usually, this will be on walls and ceilings throughout the home. It is usually desirable to paint the plaster but it is essential that a mist coat of paint is applied first.

What is a Mist Coat of Paint?

A mist coat is a watered-down layer of paint that is applied to new plasterwork to prevent layers of paint from peeling and cracking. This diluted layer of emulsion paint sinks into the fresh plasterwork and forms a bond allowing thicker coats of emulsion to be applied over the top.

When is the Plaster ready to receive a mist coat?

The simple answer is when the plaster has dried out. This can be any length of time and varies depending on temperature, moisture in the air, what plaster was used, how thick the plaster is and other conditions.

Photo shows plaster drying out before mist coat
Plaster still wet and drying out. Can take weeks to dry fully.

The average drying time in a well ventilated, heated home would be to allow 12-14 days but a good gauge is when the plaster has changed colour and that no damp spots remain at all. This can take as long as a month to six weeks. It really is worth waiting for the plaster to completely dry out otherwise it can result in some unwanted problems down the line.

You can help by adding ventilation with opening windows and improving the air flow within the home. Once the plaster has cured you can prepare it by sanding and removing any lumps or bumps that remain, if any.

Mist Coat Ratio Mix

To make a mist coat mix you will need some emulsion paint. It is important to note that this should be vinyl-free.

There are discussions over this between decorators and each has their own preference to the mixing ratio. You can start at 80% paint to 20% water to begin with and always add more water. We don’t advise going any lower than a 50/50 split though. Using an old clean paint tub or bucket mix the emulsion to water and stir thoroughly. Use a mixing stick or mixing paddle drill attachment to blend correctly.

TIP: Regardless of other’s advice, do not add PVA mix to your mix coat! PVA prevents the paint from soaking into the new plasterwork

Applying the mix to Plaster

Once the mix is ready to use immediately and doesn’t let sit. Due to the paint being thinned and watered down there is more chance of a mess. We advise protecting with as many dust-sheets as possible. Overcoats all areas of new plaster by applying the mist coat mixture either by brush or roller.

Normally one mist coat is enough but if the plaster is sucking up the mist coat really quickly then a second coat maybe required.

Best Paint to Use

Any vinyl free emulsion paint can be used. The emulsion that is being used to coat after the mist coat can be used but any emulsion that can be bought can be used as it is being watered down. Make sure it is water-based and vinyl free.

It is best to use a white or very light emulsion so that subsequent coats of paint blend well.

Mist Coat Drying Time

Mist coats can dry very quickly but we would still advise that you leave a clear 24 hours before overcoating with any paints. Once dry you can now get on with the task of applying colour to your room.

Materials Needed for task:

  • Empty clean bucket
  • Mixing Stick or Paint Paddle
  • Standard water-based emulsion
  • Paint roller or paintbrush and roller tray
  • Dust Sheets

Conclusion

Although there is a lot of waiting around in this process it is best to have patience when leaving plaster dry and applying a mist coat. Sometimes there is always a time where you may have to cut down on time but you always run the risk of paint failure down the line. Try to factor time in if planning any plastering in your house over the next few months.