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Newly skimmed walls. I'm hearing of this mythical "mist coat". What's the difference between a mist coat and undercoat (I know a mist coat is diluted, but what I mean is why can't I just use an "undercoat")? I have seen some premixed "mist coats" (or something that supposedly does the same job):
screwfix.com/p/n…004
wickes.co.uk/Wic…443
Are they any good?
Is it really even necessary? Reading a few different things online from, it's not required at all and seems to be something that's recently cropped up, to it's been used since Roman times.
I'm pretty sure I've never done it before and not had a problem.
Hello and thank you.
Newly skimmed walls. I'm hearing of this mythical "mist coat". What's the difference between a mist coat and undercoat (I know a mist coat is diluted, but what I mean is why can't I just use an "undercoat")? I have seen some premixed "mist coats" (or something that supposedly does the same job):
screwfix.com/p/n…004
wickes.co.uk/Wic…443
Are they any good?
Is it really even necessary? Reading a few different things online from, it's not required at all and seems to be something that's recently cropped up, to it's been used since Roman times.
I'm pretty sure I've never done it before and not had a problem.
Hello and thank you.
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sorted byAs for premixed stuff? To me that's like pre-diluted screenwash, you're paying for a whole load of water. We just use watered down white paint, then the same paint again for the base coat, then the colour on top (two coats if necessary). It might sound excessive, but we've had good results from it.
You can water it down if you want but it isn't necessary, I don't spend the time watering it down.
The technical behind this is that new plaster is porous like a sponge, it sooks up everything in the enviroment and the quicker you mist coat it once the plaster is dry, the better, as it will seal the wall.
Same as bare bricks when it rains.
Breathing, smoking, cooking, condensation, anything that distributes things into the air, your bare plaster will sook it up and "stain" it which will cause you problems painting it in the first place if you leave it too long unsealed.
Vinyl matts, silks, eggshells, undercoats etc are no good, because they do not penetrate into the plaster, they sit on top of it like a film.
So months/years down the line, you could probably manage to peel the paint off like wallpaper and get back to the bare plaster if you use these types.
All paint types are made up with different ingredients depending on what they are used for.
Things like 'bare plaster paint' are just a con.
They have essentially put watered down matt emulsion in that tub and named it 'bare plaster paint' and are selling it for more money than a plain matt emulsion because it's all singing and all dancing 'bare plaster paint'.
It's the exact same thing when people buy 'kitchen and bathroom paint'. Kitchen and bathroom paints in the trade are Silk emulsion. It IS silk emulsion.
"But it says it's anti-mould" all paints have an element of fungicidal additive in them, just durable paints like silk, eggshell, have more quantity of it put in them when they are being made compared to matts.
But B&Q etc specifically name it as 'kitchen & bathroom' paint with it's own aisle, so they can shove a higher price tag on it - when you could buy just silk for less.
To conclude:
Buy MATT emulsion.
Water it down or don't.
Mist coat your walls. (edited)
I've always just used a watered down top coat on the bare plaster, any most of the paints I use give the recommended ratio on the tin. The increased water content means that when the plaster sucks the moisture out of the paint, it's still wet enough to cure properly.
Mist coat is necessary on newly plastered walls as watered down emulsion soaks into new plaster better. I have used Screwfix product on newly plastered ceilings and it seems to work well. Probably a cheaper solution than using a mist coat of one of the better (ie more costly) emulsions.
It's sound reasoning, after all you can get all sorts of values online. From memory it's usually mentioned on the tin for the particular paint (as Wibbleboy mentioned above). That is the ratio to go for, as it depends on the paint itself. Going off a generic 'seen on the internet' ratio is not the best option.
Read the data sheet for the paint. Also read the drying and recoat times.
For your information
Durable emulsions take longer to dry and retail paints.. DIY.... have thixotropic agents in which make them unsuitable for mist coating.
No easy answer. Just too many paints about.
I use acrylic primer undercoat over new plaster most of the time.
Tinted or white..
Then over with whatever the home owner wants.
New builds use contract emulsion to allow walls to dry out over the coming months through the paint, but over skims dry in a few days so I never use contract emulsion. No need. Walls and ceilings are dry. (edited)
That's my experience too, I used undiluted matt emulsion as a base coat on a couple of freshly plastered walls at our old house back in 2010, there was no sign of any peeling or flaking between then and when we moved out in 2017.
Yes - the Wickes link is the one I used.
Do you remember what stuff you used? Is it the same as linked in the question?
Reason I wanted the easy mixed stuff was just so I don't have to mess about getting ratios right. Again, just reading online, it seems to vary from 20% to 50% water, whereas on manufacturer's labels they suggest a much lower water content (10-30%).
Plus having to sand the rough surface it produces unless you don't care about that.
Go look up leyland and dulux technical videos explaining. You will hear them say the overuse of contract emulsion in the UK as a primer. It is not a primer!
Give me a 10lt of contract matt I'd fill with cat litter and throw in skip. Ha. (edited)