Today’s article is all about painting bare plaster. I’m going to be telling you what paints to use, how to use them and in the process reveal the old secret that the big DIY chains might not want you to know.
Painting new or bad plaster has for some reason become an incredibly perplexing, complicated subject for DIYers so I’m going to keep things as simple as possible in this article. I’ll split it into three sections; the easy part (surface preparation) and then the two more tricky areas – choosing the right paint and finally choosing the right tools taking into account your project and budget and whether these be pro, semi-professional or cheaper DIY tools.
How long after plastering can you paint?
How long after plastering you can paint depends on the type of plastering in your home as well as environmental conditions. You should leave it for at least 4 weeks, if not longer, as the plaster needs to be bone dry before painting.
What do we mean by surface preparation? Well there are two points to make here. The first one is the plaster must be completely bone dry before you start painting. And working out if your plaster’s dry is pretty simple. If it’s still drying, you’ll see obvious damp patches. The second point to make is now is it time to remove any slight imperfections on the surface before painting.
Examples might include minor trowel marks which can be filled with a bit of EasiFill filler and can be quickly smoothed over with some 180 grit sandpaper. I recommend 180 as I think 120 is still a bit rough as it can scratch the wall. I know this is a pain but it’s the way to achieve a truly professional finish with your painting.
Choosing your paint
So the plaster’s dry, the surface is prepared and now we need to prime or seal the plaster with one to two coats of paint. But why do we need to seal the plaster and what paint should we use?
Well the trouble at the moment is the plaster is in a very porous state so if we just paint a normal emulsion onto that plaster, the plaster will suck the water out of the emulsion, the paint will dry too quickly and then right away or possibly later when you apply a second or third coat you’ll find that the original coat starts peeling off because that first coat basically has no roots or key onto the plaster.
So what you need to do is apply a watered-down coat of emulsion and it’s just watering down – that is why it’s called a mist coat because it paints a lot thinner, it sinks into the plaster and in the process properly bonds and adheres to it which gives you a really good base coat to paint on top of.
A couple of final points: never use a paint with the word vinyl in it or for that matter a diamond matt or flat matt for the mist coat.
And secondly, in spite of what you may have learnt on the Internet, never be tempted to apply a PVA coat to the wall before painting. Why? With the vinyl additive in the emulsion or the PVA coat all you’re doing is basically creating a skin over the surface of the wall. Now this is going to cause a massive problem down the line if you ever need to repair or sand that wall and in the worst case scenario you could at some point find that that skin starts peeling off.
So I tend to use contract matt emulsions like Armstead to make my mist coats because they’re good quality and cheap and a 10 litre tub usually costs less than £25.
But a word of caution – don’t assume that all contract emulsions can be thinned down. For example, the Valspar contract emulsion specifically says on the back of the tin that it cannot be thinned down whereas the Dulux and the Leyland contract matt both direct to be thinned down if you’re painting on to bare plaster.
So it can be a bit of a minefield and I advise you to read the back of the tubs carefully before you buy your contract matt emulsion.
In terms of a percentage that you can thin your paint down to – you will not get a definitive answer on this because opinions vary so widely. Armstead say up to 20 percent water, Leyland say one part water to nine parts paint or 11% and Dulux say up to 10%.
Personally I go a lot higher than this up to a 50/50 ratio but that’s just my experience after doing a lot of mist coats and never having so much as a peel or a crack in the paint but it takes a brave man to go against manufacturer guidelines so I would suggest to you the sweet spot is somewhere between 15 and 30 percent.
Ready-made mist coat
So that’s preparing your own mist coat but what happens if you just can’t be bothered? Well, as luck would have it there are specialist products on the market now that you can get from most hardware stores for £20 for a 10 litre tub. These paints apparently do not need to be watered down and can be applied to the bare plaster.
To be brutally honest, it looks far too thick to my mind to be painted directly on to bare plaster and I don’t have much confidence in it. That’s not to mention that it’s the same price as contract matt which will obviously go much further once watered down.
Tools for the job
Masking goggles are always a good idea when sanding and I’d also suggest a good sanding block to go with the 180 grit sandpaper mentioned earlier in the article.
We’ve gone through the paint but a 15 litre paint scuttle is a must-have piece of kit when you’re mixing large quantities of paint. And working with rollers, you’ll need a larger paint scuttle. I’d also suggest going for a monster 15 inch roller. A 2 to 4 foot extension pole is a good investment too. It massively increases your reach meaning you can cover larger areas more quickly. And for messy jobs like mist coating it’s great because it stops you getting splattered with paint.
I’ve used a 4 to 8 foot pole much less but it would come into its own for high ceiling rooms and painting outside of the house.
You’re also going to need a mixing paddle and drill driver to thin down the paint. For getting into the corners you might consider getting a mini roller and sleeve, a mini paint scuttle and a few large paint brushes. My advice would be to go for a Purdy jumbo mini roller rather than a standard mini roller.
You can also get plastic sheeting to protect the floor, several dust sheets including a heavy-duty one which would be more than adequate to stop the paint getting through. The plastic sheeting will do a good job at protecting beams.
Budget vs quality
Some really important buying advice – quite frankly there’s no comparison between budget and expensive pieces of kit. Take rollers for example. The difference in quality and the roll of frames is obvious and the roller sleeve you buy from your typical DIY store are going to be narrower in diameter and therefore will carry less paint and give you less coverage.
If you can’t find good gear online, get yourself down to your local decorators centre – whether that’s Brewers, Dulux or Johnston’s and see what they’ve got to offer. Don’t be intimidated – they’re not just for trades.
They massively welcome members of the public and you’re going to get much better quality advice than you get from your typical national DIY chain and you’re going to get a better quality of product because they’re catering for professional tradesmen.
Now I’m conscious it could be seen as being a bit arrogant “look at me with my smart tools” and whatnot, so have a look for yourself at the alternatives being offered in places like that. Remember that tools like this are going to last and they’re going to make your painting so much easier.
Painting bare plaster
I wouldn’t use a smooth roller for this – instead I’d recommend using a semi rough roller due to its high absorption and transfer rates which is ideal for a mist coat.
Once you’ve got your roller, it’s a quick stir with the Armstead contract matt emulsion and then pour 4 litres into the paint scuttle which when watered down ends up being a perfect amount to do your ceilings and four walls.
Side note: you might notice the consistency of the unwatered down paint is pretty much identical to the bare plaster paint that you don’t have to water down which is why I’d recommend the contract matt instead of the pre-made stuff.
The massive benefit of having a 15 litre capacity paint scuttle is that it gives you the ability to mix large quantities of paint. If you use something like a roller tray which holds less than 1 litre, you’d have to mix the paint in a larger bucket and constantly decant it into the tray.
So into the 4 litres of paint, initially pour just over a litre of water and mix it up with the paddle mixer. Get your roller and pick up some paint. You might find that although it’s a fairly watery consistency in the scuttle, when you start rolling it onto the wall you might not be happy with the consistency as it might be too thick for your liking. If that’s the case, put a further half a litre into the mix and that should be enough.
Applying a mist coat is meant to be a really messy job but you’ll notice just how little paint actually falls on the floor while when you’re applying it which is a testament to just how good the high absorption, high transfer roller sleeves really are. And it’s particularly remarkable when you think just how much you would’ve watered down the paint.
After completing this article, I decided to do a test with the bare-plaster specific paint to see what results I could get. Admittedly, the coverage is excellent – it’s more opaque than the heavily watered down mist coat but panning around the room made me wonder whether that increased opacity is really important given that I’d be covering it in a minute with two coats of high opacity flat matt.
I also used two litres of the bare plaster paint on one wall compared to four litres for four walls and ceiling with the contract matt. So clearly the contract matt emulsion if watered down goes a lot further and I appeal to the inner DIY guru inside of you to simply buy yourself a mixing paddle and water down a good contract matt emulsion rather than going to the expense of buying a bare plaster paint.