Don’t Make These Mist Coat Mistakes

Applying a mist coat is a crucial step when painting new plaster, yet many DIYers and even professionals make costly mistakes. Skipping or incorrectly applying a mist coat can lead to peeling paint, uneven finishes, and a paint job that doesn’t last. In this guide, we’ll cover the biggest mist coat mistakes and how to avoid them for a flawless finish, with specialist primers for plaster and the topcoats to paint them with.

 

 

New plaster must be completely dry before applying a mist coat. Plaster typically takes two to four weeks to dry, depending on the thickness, temperature, and ventilation of the room. Painting over damp plaster traps moisture beneath the paint, leading to peeling, flaking, and bubbling. Moisture can also interfere with the bonding process, causing weak adhesion between layers of paint.

Painting too soon can also lead to damp patches appearing through the paint as moisture tries to escape. This may cause further issues like mould growth or a musty smell in the room, making it necessary to repaint sooner than expected.

How to Avoid This Mistake:
Wait until the plaster is an even, light colour with no darker patches. Increase airflow by opening windows or using a dehumidifier. If unsure, use a moisture meter to check that the plaster is dry before painting. Patience at this stage prevents long-term issues.

 

 

A mist coat should be a thinned-down emulsion or primer that soaks into the plaster, creating a bond between the surface and the topcoat. If the mix is too thick, the paint will sit on the surface rather than being absorbed, leading to poor adhesion. If too thin, it may not properly seal the plaster, leaving some areas unprotected.

Some DIYers assume that a 50:50 ratio of paint to water is the best approach, but this depends on the type of paint used for the mist coat. Some contract paints require less dilution, while thicker emulsions may need more. Failing to adjust the mix can lead to an uneven base.

Ideal Mist Coat Ratio:
Always check the paint tin for manufacturer recommendations. If unsure, contact Rawlins’ Technical team or leave a comment on this post further below.

 

 

Many assume any emulsion paint will work for a mist coat, but vinyl and silk paints can create a barrier that prevents adhesion. These paints form a less porous layer, leading to future peeling or flaking. Additionally, silk emulsions can leave a glossy finish that may not bond well with subsequent layers.

Best Paint for a Mist Coat:
Use a non-vinyl, water-based contract matt emulsion, or a specialist problem-solving primer such as Drywall Pro for the mist coat. This allows the plaster to breathe and provides the best base for topcoats. Using the wrong type of paint at this stage could lead to costly rework.

 

 

Even if the plaster looks smooth, it’s essential to prepare the surface before applying a mist coat. Dust, plaster residue, and imperfections can lead to an uneven or patchy finish. Grease, handprints, or residual moisture can also cause issues.

Proper Preparation Steps:

• Lightly sand any rough areas with fine sandpaper.
• Wipe the walls with a damp cloth to remove dust.
• Use masking tape to protect skirting boards and ceilings.
• Check for cracks or uneven areas and fill them before mist coating.
• Ensure lighting in the room is sufficient to highlight any imperfections before painting.

 

 

Many DIYers apply the mist coat too heavily, causing drips, streaks, or patches that dry unevenly. On the other hand, applying it too thinly can result in poor coverage, leaving porous spots that may absorb too much topcoat.

Best Application Method:

• Use a 9-inch medium-pile roller for large areas.
• Cut in with a 3-inch brush for edges and corners.
• Work in sections, rolling in a ‘W’ motion to spread the paint evenly.
• Avoid overloading the roller to prevent drips and streaks.
• Keep an eye out for runs and correct them immediately.
• If spraying, use even strokes and maintain consistent distance from the wall.

 

 

Rushing into the topcoat before the mist coat has dried can cause adhesion issues and a poor-quality finish. The mist coat needs time to soak in and bond with the plaster before applying further layers of paint.

How Long Should a Mist Coat Dry?
Leave the mist coat for at least 24 hours before applying a topcoat. In colder or more humid conditions, drying may take longer. Use a fan or dehumidifier to help speed up drying in damp environments. If the mist coat feels tacky, wait longer before proceeding.

 

 

One mist coat is usually enough, but if the first coat is heavily absorbed or patchy, a second coat may be necessary to achieve full coverage and proper adhesion.

When to Apply a Second Mist Coat:

• If the first coat dries unevenly.
• If the plaster remains highly absorbent after the first coat.
• If the wall still feels chalky or powdery after drying.
• If you notice variations in colour, indicating uneven absorption.
• If applying a darker colour, ensure full coverage with an extra coat.

 

 

A mist coat isn’t a finished surface – it’s a base for your topcoat. Some people mistakenly believe it’s sufficient as a standalone paint layer, but this will not provide a durable, finished appearance.

How to Finish the Job Properly:

• Apply two coats of topcoat paint after the mist coat has dried.
• Use a high-quality emulsion for a durable finish.
• Allow each coat to dry fully before applying the next.
• Choose a paint finish that suits your space, such as matt for a soft look or satin for easy cleaning.
• Lightly sand between coats for an ultra-smooth finish.

 

 

What Happens If I Skip the Mist Coat?

The topcoat will soak directly into the plaster, causing patchy and uneven colour. It may also peel or flake off over time, resulting in a poor-quality finish that needs repainting sooner than expected.

Can I Use PVA Instead of a Mist Coat?

No. PVA forms a seal that prevents proper paint adhesion, leading to peeling and poor durability. Plaster needs a breathable base, which a mist coat provides.

How Can I Tell If My Mist Coat Has Worked?

After drying, press masking tape onto the wall and peel it off. If the paint stays on the wall and doesn’t flake, your mist coat is successful. The surface should feel smooth and evenly coated.

What’s the Best Paint for a Mist Coat?

Use a non-vinyl, water-based contract matt emulsion mixed with water. Avoid silk, vinyl, or PVA-based paints. Look for products designed for newly plastered walls for the best results, such as Zinsser products including Gardz and Drywall Pro primers.

By avoiding these common mist coat mistakes, you’ll ensure your wall stays painted longer, looks better, and stays free from flaking or peeling. Allow your plaster time to dry properly! Taking the time to get this step right makes all the difference, resulting in a professional-quality finish that will stand the test of time. Need help painting your interior walls? Read our blog for more tips.