Painting new plaster is usually an essential step on the road to completion if you have had any major home improvement or building work done. Or indeed have had any walls or ceilings plastered or skimmed, painting will be essential.
A quick skim coat of plaster can quickly and easily rectify many types of imperfection in walls and ceilings and give you a clean, flat and even base to work from. Once your new plaster is painted, you should be left with a clean, fresh and inviting room space.
Likewise, painting new plaster is often one of the finishing stages of major building works such as the construction of an extension or loft conversion.
If this is your first time painting new plaster, you will probably have quite a few questions; What type of paint should I use? How long do I have to wait before I can get painting? How long does plaster take to dry? etc…, all of these questions and more are answered below, so read on.
How Long Must I Wait before Painting New Plaster?
When a wall or ceiling is plastered the wall is obviously wet. A very frequent question to DIY Doctor is; How long must I wait before I can start painting new plaster?
Unfortunately, there is no definitive answer to this question as all walls and ceilings will dry out at different speeds, depending on many factors such as humidity, air temperature, the type of property, the type of plaster, how many coats of plaster there are, whether the central heating is on and many other factors.
As a very rough estimate, in a normal centrally heated and well insulated house in summer time, you can be pretty sure of safely painting after around 2 weeks, but this isn’t guaranteed.
To be 99.9% sure that your new plaster is safe to paint, we would recommend waiting for around 3 – 4 weeks, but in some situations it can take as long as 6 weeks or more.
In extreme situations, a fully plastered wall, i.e. two or even three coats of plaster, can take months to dry out fully!
So, how do you really know when it’s safe to paint new plaster? The best gauge for this is the colour of your new plaster. The first image below shows a newly plastered wall. As you can see, the plaster is quite dark in colour as it has only just been laid on.
The second image below that shows the same area after about a week. As you can see some areas are much lighter now indicating that they have dried out, but there are still quite a few dark patches indicating that they are still damp and have a fair amount of drying to do.
The third image below shows the plaster after about 2 and half weeks. As you can see the plaster has now dried out completely and is a uniform light colour across the entire area, giving a good indication that it is now dry and safe to paint.
One final thing to throw in the mix at this point is the type of plaster you’re intending painting on. There are quite a few different types of plaster (information on these can be found in our plastering and skimming and types of plaster project) and each has it’s own approximate drying time.
However, any approximate drying times will also depend on what the plaster has been applied to e.g. direct to plasterboard or on to a bonding coat over brickwork, concrete blocks etc….
Do I Really Have to Wait That Long?
The short answer to this is yes! Wait until it’s totally dry and the same colour as in the third image above.
The reason for not painting new plaster before it’s completely dry is that most paints will simply form an air tight skin over the wall.
The moisture from the new plaster is then trapped behind this skin and cannot evaporate off. The damp then either retreats back into the wall where it develops mould growth or reacts with the salts in the wall to become Efflorescence. Either way you have a problem on your hands that is incredibly difficult and potentially costly to deal with.
Can I Make my New Plaster Dry Quicker?
In short, no! To get the best possible finish results, fresh plaster should be left to dry out naturally.
As with many materials and finishes in the building trade that require drying time, if you try to rush this drying or curing process then in most cases the “bond” between surfaces that is created during this process is weakened and in this case your new plaster won’t stick fully to the surface beneath it.
Additionally, rapidly drying freshly laid plaster can also shrink it, causing cracks to appear in the surface.
Despite the above, there are things that you can do to aid the natural drying process e.g. ventilation.
If possible, open all windows and doors to help create as much ventilation and through-draft as you can as this will help with the natural drying of your new plaster.
What if I’m in a Real Hurry to Paint my New Plaster?
If you are in a hurry to paint your wall because Grandma is coming to stay, there are paints on the market called Microporous Paints. These paints allow the surface of the plaster or indeed artex to carry on breathing and evaporating while they are drying out. They can be found in a lot of DIY stores and decorators merchants.
Microporous paints are generally a lot thinner than ordinary water or solvent based paints and in a lot of cases, once the wall is dry, it is recommended that you over-paint them with emulsion because of this, but only when the plaster is totally dry.
If you are going down this route, please read the manufacturer’s instructions on the container for information regarding thinning down and applying the first coat (mist coat) onto new plaster.
Although this method is a solution if you are in a real rush, we would always recommend waiting the required drying time before painting new plaster. In the majority of cases, you will never get a finish you are totally happy with when rushing, regardless of whether you use specialist products or not.
Do I Need to Prepare New Plaster Before a Mist Coat is Painted on?
The answer to this really depends on who has done the plastering. If you have hired a time-served professional plasterer to do the work for you, you can be pretty sure that the results of his labours are going to be of a high standard.
Despite the quality of the work of a professional, corners of trowels can catch, dust and debris in the air can settle of freshly plastered surfaces and other workers onsite can accidentally mark surfaces with tools, bits of timber, hard hats etc….
If you have had a go at the plastering yourself then you may have left a few trowel strokes or slight imperfections that need a little attention.
With the above in mind, if you do notice any marks, debris, scratches, lumps etc…. in most cases these can be rubbed out using sandpaper. Use paper somewhere between 120 and 240 grit to gently rub any marks out.
Gently run the paper over the surface. Don’t rub too hard or too much in one place as you will end up causing more damage by creating further dips or indeed polish the plaster to a point that the paint will no longer adhere to it fully. Using a flat rubbing block is a good idea as this will help ensure the paper stays flat to the surface and that you don’t create any dips.
Regularly check progress by using your hand and finger tips, and running them over the surface. Once the mark or damage has been rubbed out you should feel no difference between the affected area and plastered surface around it.
If you find any dips in the surface, these can be filled after you have applied your mist coat as you will be able to see the extent of the damage a little better. Using a suitable filler, apply it over the damaged area using a filling knife, wait for it to dry and then sand it back to match the surface around it. It can then be painted.
What Type of Paint Should I use on Newly Plastered Walls?
When it comes to actually painting new plaster, the first coat that you apply will be a mist coat. I can now hear you asking; What’s a mist coat? Well, a mist coat is essentially a watered down matt emulsion (more about this below).
When we say a matt emulsion, we mean the general purpose water-based (not oil or vinyl based) matt emulsion paint that is available from pretty much all DIY stores.
A water based (and diluted) matt emission will bond and adhere to the plaster, giving you a good base to work and build on. This paint-type will also allow the plaster beneath it to breathe, avoiding trapping any moisture that could cause damp patches and other issues down the line.
Do not use vinyl or silk paints! As these types of paint dry, they form a “skin” that sits on top of the bare plaster and does not bond with it meaning that it can easy flake or peel off.
Likewise, don’t be tempted to apply PVA or similar to bare plaster as a sealer, although some do recommend this! As PVA is essentially a waterproof sealer, it will prevent the paint from soaking into the plaster and through this creating the necessary bond that will ensure it stays stuck to the plaster itself.
Finally, use a light coloured matt, preferably white. A light neutral colour will provide a good base for your finishing topcoat paint, which can be any colour of your choosing.
Priming and Sealing New Plaster With a Mist Coat
Now that we have established that we should use a white Matt Emulsion for our mist coat, it’s also a good idea to quickly go over why we need to prime and seal a newly plastered surface.
New and freshly laid plaster (and also freshly laid artex) is very porous indeed. If you apply any kind of ordinary paint directly onto either of these surfaces, any moisture will immediately be sucked out of that paint before it has a chance to dry naturally.
In simple terms this leaves the paint going dry on the surface only and because the moisture has been sucked out so quickly, it has no "roots" or "key" to bond correctly. This “surface paint” may then soon start to blister and flake off.
It is for this very reason that it’s necessary to "prime" or "seal" the surface first using a mist coat paint. Sealing means applying a coating which is diluted enough to enter the pores of the material with the emulsion or liquid with which its mixed.
When applying a mist coat paint to a surface such as this, sometimes you can even hear the bare plaster or artex sucking the moisture from the mix.
How Should I Make my Mist Coat?
When your plastered surface is fully dried (and the colour of the third image above), it’s now ready for your first mist coat.
To make your mist coat, it’s best to mix it up in a paint kettle or small bucket to the ratio of 4 parts paint to 1 part water:
Mist Coat Mix Ratio
- 4 parts paint
- 1 part water
There is a huge amount of conflicting advice on what the perfect mist coat ratio is, but to be honest, anything from 70% paint – 30% water to 80% paint – 20% water should be fine.
Use a suitable measuring jug to measure out the correct quantity of matt emulsion paint and then pour it into your paint kettle. Then measure out the required quantity of fresh, clean water and pour that in too and mix it thoroughly using a clean stick or even drill with a mixing paddle.
make sure you mix the components up thoroughly! A good few minutes should be adequate.
Once mixed, apply using a brush to a small area of bare plaster. If the plaster does not seem to be sucking up the liquid quickly, more water can be added to a maximum of 1 part water to 1 part paint.
If you are sure that the mix is correct, you can get it on the wall.
As the mix is quite runny, this is a messy job; it goes everywhere! Ensure any carpets and furniture are totally covered (or ideally moved out of the room). Also the mist coat mix will get all over you, so cover yourself too. At minimum old clothes should be worn, but if you have one, a disposable coverall is best.
When it comes to actually painting new plaster, you have really 2 options: a paint brush or a roller.
A large paint brush (around 4 inches) is really the best option as it gets a fair amount on the wall with the minimum of splash. You can use a roller and this is certainly the quickest method, but it’s also the messiest by far!
When it comes to drying time for your mist coat, due to the porous nature of the plaster it will dry very quickly, but for completeness, allow 24 hours for your mist coat to dry fully.
At this point, it is also worth mentioning that there are now specialist paints available, designed specifically to be applied to bare plaster without the need for it to be watered down, that still allows the plaster below to breathe.
Here at DIY Doctor, we have never used these products before as we prefer to stick with the traditional mist coat method as we know this works, but we do know many that have tried them. All we will really say on them is we have heard mixed reviews; some that have seen great results and others that haven’t!
How Many Mist Coats do I Apply?
In short, it’s rarely necessary to apply two mist coats of sealer, but it will not harm the surface either.
If you want to go down the “belt and braces” route then applying a second mist coat is a good idea. Apply it using the same techniques as above and again, give it 24 hours to fully dry.
When all plastered surfaces are sealed and dry, you can continue to paint as normal and apply any top finishing coats.
If you are working with walls or ceilings in kitchens or bathrooms, some paint manufacturers make a special kitchen and bathroom paint which have a great range of colours.
The humidity in kitchens and bathrooms allow water based paints like normal emulsion, to soak up the water vapour which can make them unstable and likely to peel or harbour mould spores. With this in mind, it’s best to use the correct paint for the area you are dealing with.
In summary, there is no substitute for leaving lots of time to allow your new plaster to dry fully before painting it. Wherever possible err of the side of caution and leave it as long as possible before painting new plaster, but we also recognise sometimes time is not on your side and you just have to get it painted, but be aware of the risks and issues that this could bring.
All project content written and produced by Mike Edwards