Plaster is a building material that is primarily a protective coating for your walls. The temperature along with humidity and other factors will affect the time it takes for plaster to set and how well it sets. How you manage these factors will have an impact on the protection and finish you get in your home in the end. We all know that when it’s hot, the plaster dries quickly and when it’s cold the plaster dries slower. You can plaster in any weather but what temperature is optimal?
The optimal temperature to plaster a wall is around 44 degrees Fahrenheit (4.4 degrees Celsius). As well as heat, wind, humidity and exposure to the sun will all affect how well the plaster will set. Managing all of these contributing factors will lead to the best finish
So we’ll get into the best practice of plastering a wall depending on the weather conditions you’re dealing with, but before we do its useful to understand a science a little bit. Let’s get into why temperature, wind and the sun matter when it comes to applying plaster.
Why temperature, wind and the sun matter when you are plastering a wall
Okay so when water is mixed with plaster, it creates a chemical reaction, and the mixture takes on the plaster state you’re used to before applying it to a wall. The amount of water in the mixture will affect the stickiness of the mixture.
If it’s too hot or too cold, windy or sunny the moisture can be lost which can lead to the plaster cracking and not setting as you would expect it to. Let’s look into each of these scenarios, understand what happens, to look at options to protect your plaster.
When it’s too hot or sunny (i.e. when temperatures go above 90 degrees Fahrenheit or 32.2 Celsius), materials tools, and the wall itself get warm which encourage moisture to evaporate from the plaster. This reduces the tensile strength of the plaster and can cause it crack.
When it’s too cold (i.e. when temperatures go below 32 degrees Fahrenheit or 0 degrees Celsius) , the plaster will freeze on the wall which will make it weaker. The plaster will literally come off on your hand. Not just that, the cool air can also absorb the moisture from the plaster too, which can also lead to cracking.
When it’s too windy similarly to when it’s hot moisture is taken from the plaster, reducing it’s workability meaning its harder to spread over the wall and is more prone to cracking when set.
In any extreme of weather, the quality of how well your plaster will set is compromised. Also, the chemical reaction when you mix the plaster with water also heats things up and increases evaporation – so that’s another consideration.
Ultimately you need an environment where you can maintain the workability of the plaster with adequate water to allow for the plaster to set properly. So how do you do that? – Lets look into it!
Handling weather conditions when plastering your wall
Okay, so the goal when plastering a wall is a smooth finish with no cracks. For that you need the plaster to be workable when applying, have good adhesion to the wall and great tensile strength to avoid it cracking or coming off.
The temperature and general weather conditions play a major part. In essence it can’t be too hot or cold or you risk your plaster cracking and falling off, and it can’t be too windy or you’ll lose the moisture from the wall. Just though it was worth re-capping – Anyway here’s how to handle it in a handy table
| Plastering in heat | Plastering in the cold | Plastering when windy |
| Work earlier for cooler temperatures | Avoid frozen surfaces – heat the room to 44 degrees Fahrenheit (4.4 degrees Celsius) | Drape a tarp over the plaster once complete |
| Mix using cool water | Mix using warm water (Max 120 degrees Fahranheit or 48 Celsius) | Keep the plaster moist by “fogging” with water |
| Keep the plaster moist by “fogging” with water | Make sure there is ventilation to keep the air moving | Reduce the number of open windows if indoors |
| Keep materials and tools away from sunlight | Store tools in a warm place to help avoid further heat loss. | Check weather reports for lower wind speeds |
If you’re still wondering why water moisture being is lost in warmer climates and cooler climates, here’s how I think about it. In heat, moisture evaporates from the plaster causing it to crack. When its cooler, the water evaporates, but at a slower pace, allowing it to settle on the surface of the plaster which causes it to crack. Too hot or too cold – there’s a problem – so it’s important to get it right!
Hopefully I’ve answered your question – but here’s some other common questions I found – so I thought I’d go ahead and have a go at answering them too.
One other thought – before you start plastering your walls – have you considered using lining paper instead? It’s considerably cheaper and is a great alternative to re-plastering. I wrote this post on it if you want to know more.
What’s the ideal temperature when plastering a large wall?
The ideal temperature to plaster a large wall ideally is around 44 degrees Fahrenheit (4.4 degrees Celsius). As mentioned above in this article you also have to consider the wind, sunlight and humidity. How you manage these is detailed above. As a rule of thumb though, I wouldn’t recommend plastering above 86 degrees Fahrenheit (30 degrees Celsius).
Larger rooms, mean a larger surface area – which means the wall is going to dry quickly, especially if its hot! To avoid the plaster drying too quickly and cracking, it’s important to make sure the wall is kept moist through fogging with water.
How long does plaster take to dry?
If you’re using plasterboard, you can expect the skim to dry between 2-3 days. If you’re plastering onto a solid background it can take anything between 5-6 days in the summer, and 7-9 days in the winter.
It sounds like a long time but it’s worth letting nature do its thing rather than trying to speed up the process with de humidifiers or too much heating which can lead to cracking and plaster falling off the walls.
Drying plaster, should windows be open or closed?
After plastering, windows should be left slightly ajar but not fully open. Why not? Well plaster can take anything from 2-9 days to dry depending on the seasonal conditions which can allow for changes in wind speeds, rain as well as other elements. You want to protect your walls as much as possible.
You can put the heating on a low temperature to help the drying process but be conscious not to have it too high i.e. anything above 62.6 Fahrenheit or 17 degrees Celsius is probably too warm. In other words let the plaster dry as naturally as possible.
It will also help to close blinds and curtains to stop the sunlight getting into room, which can also impact how well your plaster dries.
How long after you plaster can you put the heating on?
Allow the plaster in your room to dry for the first 48 hours at least. This will let the plaster bond naturally to the wall with less risk of cracking.
Are hairline cracks normal in new plaster that’s just dry?
Hairline cracks less that 1mm are not normally a cause for concern. You can paint directly over it or add some filler to cover it completely. In these situations you can safely assume that it’s a crack in the plaster and not the wall itself.
Why is my fresh plaster bubbling off the wall?
The main reason your plaster is bubbling is probably damp walls, which means you may have to get a technician in to apply a damp proof course to stop this from happening again. There could be other reasons though.
For example, there could be excess condensation in the room which could simply be a result of not leaving the windows open enough. This article from timberwise.co.uk is a really useful resource if you’re looking to fix this issue.