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One of the most pleasurable parts of any house restoration is the freshly plastered wall. The soft, smooth and pretty texture left by the plasterers is not just aesthetically pleasing but very tactile.
You quite literally have a blank canvas and a chance to add any colour you like. Some might want muted tones and pastel shades, while others want bold, vibrant colours to create a focal point. Still, no matter your colour palette, the burning question with any new plaster is how and why to paint it with a mist coat to prevent cracking and flaking.
What Is A Mist Coat?
So, for the uninitiated out there, a mist coat may sound like a spell from Harry Potter, but to those who have had the joy of painting a newly plastered wall, it is one of the essential parts of any renovation work as without this appropriately done, you could damage all the hard work and money spent on your lovely walls and ceilings.
More than one coat MUST be applied to all newly plastered walls and ceilings prior to any top coat of emulsion.
What Happens If I Don’t Apply A Mist Coat?
So, when you have fresh, new plaster on walls and ceilings, it needs to be painted, but the first two coats of paint you apply must be watered down emulsion to ensure that the new plaster does not crack or flake.
If you did apply a fresh coat of thick emulsion to your walls and ceilings, the plaster due to its porous nature will eventually crack, and the paint will flake and peel off.
Therefore, two mist coats will ensure that the watered-down paint is soaked into the new plaster and allow you to add any colour of fresh emulsion you choose.
Proper Planning And Preparation Prevent Poor Performance
As with any do-it-yourself renovation, painting, or building work you undertake, preparation is critical to getting the right finish and none more so than on fresh, new plaster.
Your friendly, jolly plasterer would have skimmed your walls and left you with this sea of dark pink plaster awaiting a lovely coat of paint, but you have to take something away before you can add anything to those walls and ceilings.
No matter how good your friendly, jolly plasterer is, there will be some blemishes on the finished plaster, slight bumps of congealed plaster and occasional trowel marks, which have to be removed before you start painting new plaster with a mist coat of paint.
Any small lumps should be removed using a scraper, and any trowel strokes can be lightly sanded out using a high grit sandpaper (Between 120 & 240) as you do not want to be too vigorous.
Once you are happy with the finish, a small, soft broom or soft, bristled hand brush will need to be used to lightly sweep any excess dust and debris from the walls and ceilings, paying particular attention to corners and skirting boards.
This will prevent your paint roller and paint brush from accumulating detritus and smearing your lovely fresh plaster.
Top Tip: Cover all flooring with dust sheets and polythene sheets, as this is a messy job!
How To Mix A Mist Coat Of Emulsion
Firstly, the paint you will use HAS to be a general-purpose water-based white emulsion paint on bare plaster. This is because gloss emulsion and eggshell paints will require more water and, therefore, more coats.
Do not be tempted to use vinyl or silk emulsions, as these will form a layer of skin on the new plaster, which could cause flaking later on.
Now the ratio of water to paint is highly contested, and each professional painter and decorator may have his or her own methods, but for the purposes of this article, I am going to recommend a tried and trusted mist coat ratio handed down to me by my father.
First Coat – This needs to be a 50/50 ratio: 4 Parts emulsion paint to 4 parts water. It is advisable to use a paint kettle for this and mix well so that the thicker paint has blended with the much thinner water.
Second Coat – This needs to be a 75/25 ratio: 4 parts emulsion paint to 1 part water. This will be slightly thicker in texture than the first coat and will cover the wall much better.
How To Apply Mist Coats
First Coat – Keep the stirrer in the paint, as it will need regular mixing if you have a large area to paint. This base coat can be applied with a brush or roller, and remember the Top Tip, as this is a messy job.
Cutting in the edges with a paint brush as you normally would and then using a paint roller you can cover the walls and ceilings in the usual way. As the ratio is quite thin then you will still be able to see the plaster underneath the paint as it will have a very light appearance.
Allow 24 hours for this first coat to dry and be absorbed by the fresh plaster.
Second Coat – This will provide more coverage as you increased the ratio of paint to water and you will see less of the wall the more you add. You should however still be able to see the pink hue of the plaster once this coat is finished, but that is standard for this job.
Again, leave the mist coat for 24 hours to dry and absorb before applying your full topcoat of any emulsion you choose, eggshell, gloss emulsion, vinyl and silk emulsion.
Now that you have secured the plaster walls and ceilings with this mist coat, you can go to town on the colours and shades.
Top Tip: Wearing safety goggles will keep the mist coat out of your eyes, especially when painting the ceiling.
Other Products On The Market
Whilst we have advised you of the own mist coat paint method, it is time to tell you that there are products out there that claim to have the ability to do this job. As we at The Big Idea have never used any of these mist coat paint products, we feel that we cannot recommend any at this moment in time.
How Long Does The Plaster Take To Dry
This is an excellent question, as the drying process can depend on the conditions in which you are in. Wet plaster should be left to dry naturally, and central heating in the room should be turned off if possible and direct sunlight can cause shrinking and cracking.
That said, the average time for a freshly plastered wall and ceiling to dry is three weeks, and therefore recommend waiting to be prepared or painted until completely dry.
If you need more clarification, then seek the advice of the jolly, friendly plasterer who carried out the work!
Again, there are products on the market and available at most DIY stores and painters’ merchants that advise that they can be applied to wet plaster that has not fully cured, but we have heard mixed reviews and not used these products and advise that you should always read the label first for the manufacturer’s instructions.
In Conclusion
This is a vital step in any renovation involving new plaster and should be adhered to in order to ensure more than one coat of thick paint does not lead to shrinking and cracking of the new plaster and, subsequently, the flaking of the topcoat of paint.
If you get the preparation and planning right, as with any do-it-yourself projects, the final result should be a perfect finish you can be proud of for years to come.
