Drying Plaster: Windows Open Or Closed? We Explain

Temperature, humidity, wind, and exposure to the sun are contributing factors to how fast drying plaster can be. But many DIYers often wonder whether windows should be open or closed for drying plaster.

Here’s an article that thoroughly explains whether to leave the window open or closed for drying plaster. Check it out.

Drying Plaster: Windows Open or Closed?

Drying plaster is not tough. Keeping the windows open is the first step. But it is important that you also pay attention to the room’s temperature.

Suppose it is too hot, such as when there is relatively low humidity, and direct sunlight, the rapid increase in temperature can mean faster drying time. The result will be a lack of proper hydration and strength, which will be visible with the cracks in the plastered wall.

Apart from opening a window or two for ventilation, you can drape the wall to control the rate at which direct sunlight causes the plaster to lose moisture.

A critical drop in temperature also presents its challenges. Cooler temperatures can cause the cement to take longer to set. Cold conditions can also make the plastered wall susceptible to efflorescence.

You want to open the windows to increase airflow. But more importantly, keep in mind that when the temperature falls below 40°F, it would be unwise to plaster because it wouldn’t matter whether you close or leave the window open.

Plaster generally sets slower during the winter. In many cases, cold air on the wall’s surface can quickly absorb warm moisture and cause shrinkage and cracks.

How Fast Does Plaster Dry?

Generally, drying plaster takes anywhere from 5 days to a week for a complete dry-out. But the speed of the plaster setting time usually depends on how much Plaster you have in the mix and the temperature you are working with, especially when using cement.

However, the drying speed of your plaster will usually depend on many factors. These factors will include the following:

1) Type of Plaster

Joint compounds, which are usually combined with water beforehand, do not set. They usually dry once they become exposed to air. They also become dry upon exposure to hygroscopic material such as paper.

Unmixed Plaster of Paris will set in a few minutes after mixing and applying the liquid paste to the work area.

Commercial plasters formulated like Plaster of Paris are usually designed to set in different setting times depending on how much work time the project may require. Some may set in 15 minutes, others 30, 45, and even 90 minutes.

Also, plaster compounds with gypsum filler dry faster than plasters with polymer and glutinous material.

However, whichever type of plaster you use, you must leave the windows open for ventilation so the plaster can dry appropriately. Closing the windows will limit airflow, which can slow down the drying time of the plaster.

2) The Thickness of the Plastering

Thickness is another important factor to consider. Thicker plastering tends to dry out slower than thinner plastering.

Work areas like crevices, large cracks, and gaps that require filling and a bonding plaster will usually take longer to dry thoroughly than a level work surface.

Significant fillings can take up to 14 days to dry out completely. When you keep the window closed, you limit the airflow, which can affect the drying time duration.

But keeping the windows open will increase ventilation and help speed up the drying time.

3) Temperature and Humidity Level of The Room

Temperature and humidity levels also determine the speed of your plaster drying out. The optimal temperature for plastering is 40°F.

Ideally, the higher the temperature, the faster your plastering will lose the moisture in it to set. But if the temperature is too high, your plaster will dry too quickly, and this will lead to cracking and hazing in your plastering job.

Humidity levels can also affect the speed of your plaster drying. When the air is dry, plaster tends to dry faster. But in damper conditions, your plaster will take longer to dry.

You can reduce or increase humidity and ensure an ideal temperature by opening or closing your windows depending on the prevailing conditions. The ventilation will allow your plastered walls to dry well without cracking or hazing.

How Can I Speed Plaster Drying Time?

Since room temperature and airflow affect how soon your plaster dries, you may face the temptation of speeding the drying time by turning up your heating system.

While this will inevitably speed up the drying time, it is not recommended. Turning up the heat in the room to speed up the drying time of plaster will result in cracks. The main reason for the cracks is the excess heat which forces the plaster to set too quickly.

The plaster, especially cement, is hydraulic. This means that the presence of water is required for the chemical reaction that results in the setting. Hence, it would be best to let it set slowly.

If you must put the heating on, it is important that you leave it at a very low temperature for a few days after you have completed the plastering job. The low setting will speed up the drying process while reducing the chances of cracks.


If you intend to use heaters to dry your plastered walls, you must direct the warm airflow to the walls to enhance the faster evaporation of moisture from the plastered wall.

The only reason you must use heaters such as heat fans is when the room temperature falls below the marked recommendation on the plaster package.

The cement in plasters is hydraulic. This means that water is the catalyst that spurs the chemical reaction, which makes the plaster set, get hard and dry.

Hence, hot temperatures pose some challenges for plastering. Essentially, moisture leaves the cement quicker as temperature rises, leaving less water for hydration. The result is a loss of tensile strength and cracks in the plastered wall.

Therefore, many cement and plaster manufacturers advise fogging and watering the wall sufficiently before plastering. If the room temperature is high, you are likely to end up with excessive cracks on the wall as the plaster dries out too quickly.

As much as possible, avoid artificially speeding the plaster drying time unless the room temperature needs to be increased. Opening the windows to drop the humidity levels for a faster drying time is best.

Some Drying Plaster Tips

– Use Quality Plaster

Also, refrain from mixing different types of plaster. Mixing different plaster types usually affects the quality and drying time of the plaster.

Stick to high-quality laster and keep the windows open for faster plaster drying time.

– Avoid Using Fuel Fossil Heaters

Gas, kerosine, and other fossil fuel heaters can cause rapid carbonation of the cement materials during the initial set and cure period. You want to avoid using such heating sources.

Instead, ensure proper ventilation into the enclosure for proper airflow to aid the initial setting and cure.

– Do Not Plaster Cement Below 40°F

Do not plaster cement when the temperature is below 40°F without monitoring the weather conditions and forecast.

Monitor weather conditions by checking out the weather forecast during the installation and curing periods for critical drops in temperature.

For heated rooms or enclosures, it would be best to have the heat source running before the application of the cement plaster.

You also want to keep the heat source running long after the plastering with the cement. This will ensure optimal working conditions before and after the setting and curing times.

It is not advisable to plaster frozen surfaces, and expect to use a heating fan to dry the plaster. Ideally, the plaster must be prevented from freezing in the first 24 hours.

Cement plaster takes longer to set in cooler temperatures. Hence plastering a frozen wall is not ideal.

Bottom Line

Technically, plaster does not dry. Rather, it sets by losing the moisture in it. For this to happen effectively, it is important to leave at least one window open for some ventilation.

Every professional plasterer knows that plaster sets slower in the winter and faster in the summer. The weather plays a major role in how fast plaster sets.

But it would be best to control ventilation and exposure to direct sunlight as much as possible. If the room has multiple windows, you want to have some of them opened. The continuous flow of air speeds up the setting of the plaster by slowly taking out as much moisture to make the plaster set.

If you cannot open the windows, it would be best to get a dehumidifier. The goal is to ensure that the amount of moisture in the air is controlled significantly so that the air is not too damp or too dry.

You want the air in the room to be relatively dry so that the moisture in the plaster can slowly evaporate for the plaster to set.

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