I’ve been a painter and decorator for the best part of 20 years and often blog for the Decorators Forum UK. I thought I’d put pen to paper and explain a little bit about the importance of a mist coat when decorating. I hope it helps.
What is a Mist Coat in Decorating?
A mist coat is the first coat of paint on bare plaster. The purpose of a mist coat is to prime and seal a wall or ceiling to create the perfect base for additional coats of emulsion. If you miss the mist coat (try saying that after a few beers), you run the risk of adhesion issues and paint failures.
You should not sand bare plaster before you apply your mist coat as you run the risk leaving a thin layer of dust which will also cause adhesion issues. Just scrape off any snots (drips or lumps of plaster) and apply your mist coat. You can sand afterwards if needed.
What is the Best Paint to Use as a Mist Coat?
A lot of decorators use a cheap contract matt as a mist coat. However, some manufacturers do not recommend using contract matt anymore, although it is still effective.
The best advice I can give you is to check the manufacturer’s instructions on the product you intend to use as your finish coat.
Most vinyl or durable matt emulsion products now advise a diluted coat of the same product. Some brands of emulsion, such as Tikkurila or Farrow and Ball require a specific primer made by the same brand. Do not deviate from these instructions as you will not be covered in the event of product failure.
What is the Paint to Water Ratio for a Mist Coat?
You would normally add a substantial amount of water to an emulsion if you intend to use it as a mist coat. The ratio of water to paint changes slightly, depending on which paint you use. If you are using a cheap contract matt, or a paint which is specifically designed for use on bear plaster, then 10% – 20% water is absolutely fine (1 or 2 parts water to 10 parts paint).
For most products, I’d suggest adding more water than this. Vinyl matt for example should be around 25% water. Some acrylic eggshell or soft sheen emulsions can be used as a mist coat, and these need to be diluted even further. Always check the manufacturer’s instructions but add a little bit more water than they suggest. I have seen many issues caused by not adding enough water to a mist coat, but not one issue from adding too much. It’s better to be safe than sorry!!
How Should a Mist Coat Look?
It really does not matter how a mist coat looks when it’s on bear plaster. You don’t need it to cover, all you need to do is make sure it adheres to the plaster and leaves a good base for additional coats of emulsion.
Can you use vinyl Matt as a mist coat?
Yes, diluted vinyl matt makes a great mist coat. Just be sure the plaster is completely dry first, as vinyl matt will not allow the substrate to breathe as well as contract matt does.
What is the Best Way to Apply Emulsion to a Wall or Ceiling?
I know this isn’t directly related to applying a mist coat, but I thought I’d include it. I actually spray most of my paint now, however most people will use a brush and roller. Simply “cut in” around the edge of your ceiling or wall with a brush, then roll the middle using a roller. Dead easy!! Always allow a mist coat to dry fully before carrying out any additional prep to your walls or ceiling.
What are the Best Tools to Apply Mist Coat?
You can apply a mist coat with any good quality emulsion brushes and rollers. However, the first coat on bare plaster can drag, so using a long pile roller and brush with a thick stock will make your life a lot easier.
My preferred roller for mist coating is the Purdy Colossus. The thick dense nap will hold loads of paint and help you distribute it evenly. Available online by clicking here.
As for the brush, there are a few I could choose from, but I’ll go Purdy again. This time, the Purdy Monarch Elite XL. These brushes are expensive, but perfect for any sort of emulsion work. They will also last for years if you look after them. Available online by clicking here.
What Happens if You Forget to Apply a Mist Coat
If you forget to apply a mist coat, or you apply an unsuitable paint as a mist coat, then you will almost certainly experience problems. These problems will not necessarily rear their head straight away, although they might.
The most common problem caused by missing a mist coat is pealing paint, but sometimes it just bubbles. You may see it as you finish your decorating, or it might happen next time you decorate the room.
Final Thoughts
Applying a mist coat is an important, but simple part of decorating a room. Always choose the emulsion you intend to use as a finish coat and check the instructions on the tin. Most manufacturers will tell you what product you need to use for a successful mist coat.
A lot of professional decorators still use contract matt, and it works well in most circumstances.
I have a building to paint (internal) which is painted in anti condensation paint.
The walls and ceilings are in very good order, it just needs a new coat of paint to freshen it.
The cost to paint this room in standard emulsion compared to anti condensation paint is vast.
Is it OK to paint standard emulsion on top of the existing anti condensation paint?
Would you advise that I apply a mist coat first to seal the surface and then apply standard emulsion?
Or would you advise I purchase anti condensation paint and use that only?
If you know exactly what paint was used before try to find technical data sheet for it and read it carefully if any limitations regarding over coating with other paints.
From my experience I never had problems with repainting over anti condensation paint using acrylic emulsion.
Hi….what if you are painting a ceiling that hasn’t had a mist coat & the paint peels off back to bare plaster when using the roller?
Is there anything you can paint or spray on which will penetrate the existing paint & stick it to the bare plaster?
Thanks
If the existing paint is very porous you can use with success Zinseer Gardz or Mathys Pegafix. These will penetrate through the coat of porous paint and bond it all in to monolith.
As a decorator coming from the continental Europe and living in Ireland for the 18 years I’ll never understand or agree to use any other than deep penetrating emulsion like Gardz or similar for the first coat over bare plaster on the quality job.
Gypsum borne plaster has to be impregnated as deeply as possible and no paint, nor any pigmented primer no mater if it’s diluted or not will do this.
Mistcoat is an evil made shortcut and it will faill at some stage if exposed to stress.. it will not fail under no stress.. will there be stress or not we never know.
And common plaster manufacturers why in the 21st century your product has pink or gray colour Good Lord?!
Can I water down silk emulsion to use as a mist coat for newly plastered ceilings? Plan is to use silk emulsion as top coat. Or can I use Matt as mist coat and apply silk on top as a top coat? Thanks
Painting bare plaster. I’m getting conflicting advice from decorators and manufacturers. My local decorators merchants say spray on Armstead Trade Contract White emulsion as it is, no dilution. Fellow decorators say never, you MUST do a mist coat 1st! Who is right?!?!
Look forward to your advice.
And if a mist coat is necessary, what ratio?
Read the TDS of the product you’re using as a topcoat. That will tell you what to use as a mist coat