How long does it take for plaster, screed and paint to dry and what will really speed up drying

Plaster dries approximately 1 day per millimeter of thickness , cement screed approximately a week per centimeter and paint is touch-dry in a few hours. These times apply at a temperature of around 20 °C and a relative humidity of up to 65%. In colder and wetter environments these times are extended, sometimes up to twice as long.

The table below will help you plan your schedule. Always compare times for common thicknesses with the specific product data sheet.

All values are approximate. The table shows in particular that anyone who plans to lay a floor based on when it will be walkable will almost always be a few weeks off.

Drying is essentially the transfer of water from the material to the air. However, air can only hold a limited amount of water vapour, and this amount drops sharply as the temperature drops: at 20°C, one cubic metre can hold approximately 17 g of water, at 10°C only around 9 g . Cold air is therefore “full” much earlier and the material has nowhere to drain the water.

In autumn, outdoor humidity often exceeds 80%, so ventilation brings air into the building that is already saturated. The ideal temperature and humidity for drying plaster is approximately 15–25 °C with a relative humidity of 40–65% , but in November you will rarely achieve this in an uninhabited building without technology.

Imagine a family house where the plasterers finish their work in mid-October. The temperature in the unheated rooms is around 10°C and the hygrometer is reading 85%. The walls are light in appearance after a week, but the plaster is still darkening in the corners. The painting scheduled for two weeks is postponed by another three weeks, and with it the floor layers and the kitchen installation.

The slow drying of masonry and plaster is not just a matter of timing. Damp walls are a breeding ground for mold in the cold season, which we write about in the article How Mold Forms on Walls .

When you ask how long it takes for plaster to dry, you are actually asking about two different things. The difference between the two is the most common source of complaints in finishing work. “Dry to the touch” means that the water has evaporated from the surface and the material is no longer sticky. However, inside, chemical hardening and the slow release of residual water are still taking place.

In cementitious materials, some of the water serves as a reactant: the cement needs it for hydration, i.e. the chemical reaction that causes it to harden. If you dry the plaster or screed too quickly, the reaction will not be completed and the material will remain softer and more prone to cracking. “Mature” therefore means the state in which the material has reached its strength and at the same time the residual moisture is below the limit for the next layer. Parquet laid on a substrate that was “visible dry” may therefore start to lift after a few months.

Accelerating the drying of a building is based on a simple principle: the air must be warm, dry and moving. However, each of these factors has its limits.

What really helps

A stable temperature between 15–20 °C, which you increase gradually, not in sudden steps, helps. Also, active moisture removal from the air, thanks to which you are not dependent on the weather, and a gentle air flow along the walls, which removes the saturated layer of steam from the surface.

What is harmful?

Rapid heating immediately after applying plaster or screed is the most common mistake. The surface dries faster than the core, creating tension and with it hairline cracks, and in the case of screed, bulging of the edges.

The opposite extreme is closed windows without any technology. The humidity in the room quickly rises above 80%, drying almost stops and water starts to condense in cold places. So if you are not using a dehumidifier, ventilate several times a day . If you are using a dehumidifier, keep the room closed so that the device does not constantly bring in new humid air from outside.

How to quickly and safely reduce humidity in the interior of a building? A heater will increase the air's ability to absorb water vapor from the material, and a building dehumidifier will condense this vapor and drain it into a tank or through a hose to the drain.

When drying walls and floors, the rule of sequence applies. For the first 2–3 days after applying cement screed or plaster, leave the material undisturbed, without drafts and at a temperature of approximately 20 °C. Then turn on the dehumidifier and maintain the temperature between 18 and 22 °C . The article How to choose a dehumidifier for the type of space discusses the selection of the appropriate power.

In larger spaces, it is worth adding industrial fans that will distribute dry air into corners and behind partitions. For safety reasons, do not place electrical appliances in puddles or on fresh ground, and route cables so that no one can trip over them.

The residual moisture content of a screed is the amount of water remaining in it after it has dried out visually. This value is decisive for the floor covering, not the number of days since pouring. The usually stated limits are up to 2.0% for cement screed and up to 0.5% for anhydrite screed, measured by the carbide method, and even lower for underfloor heating (cement – 1.8% and anhydrite – 0.3%).

1. Observe the minimum drying time according to the table and technical data sheet.
2. Two to three days before the measurement, turn off the dehumidifier and heating so that the surface does not affect the result.
3. Perform a foil test : stick a piece of PE foil measuring 50 × 50 cm onto the screed and check after 24–48 hours whether water has collected under it.
4. If the film is dry, order a measurement using the CM method (a carbide test in which a sample from the depth of the floor screed is crushed and the pressure of the gas produced by the reaction with water is measured).
5. Take measurements in several places, especially at the outer walls and in the corners.
6. Have the result recorded in the protocol.
7. Electronic moisture meters with tips or contact surfaces only provide an approximate reading. When deciding whether you can glue parquet or vinyl, rely on the CM method.

You don't have to buy dehumidification equipment that you'll use once every few years. You can rent dehumidifiers with various capacities from the Ramirent network.

Electric heaters and fans are also available. The approximate rental price for a dehumidifier with a capacity of 60 l/day and more starts at €20 excluding VAT per day, an electric heater of 5–9 kW at €14 excluding VAT per day. If you are not sure what capacity and how many pieces of equipment you need, use professional advice or stop by the nearest branch.

It is worth combining a dehumidifier with gradual heating and always check the residual moisture of the screed before laying the floor. View the complete range of equipment for rent in the Energy, Heating and Lighting category.