Knowing how long to wait for screed to dry can be complicated and depends on a number of factors. Yet it is also important to get right. Proper drying time is essential because when screed is laid down, it contains a significant amount of moisture content. This moisture needs to evaporate fully before any floor covering, such as tiles or wood, can be installed on top. Rushing this process can lead to disastrous consequences: the trapped moisture can cause the floor coverings to warp or become damaged over time. Insufficient drying time may also result in an unstable base that can compromise the integrity of the entire flooring system.
How long does it take screed to dry?
On average, a sand and cement screed takes around 1 day per millimetre up to 50mm and 0.5mm per day for any depth over and above this. For instance, a 75mm screed would typically require 75–100 days to dry in optimum conditions.
Similarly, liquid screeds typically require 1 day per millimetre up to 40mm and 0.5mm per day over this; a 75mm layer would need approximately 75–110 days to dry in optimum conditions.
Yet, liquid screeds can offer improved drying times by reducing the thickness of the screed down to 40mm, halving the drying time. In addition, most liquid screeds will also have an even faster drying screed in their range reducing this time even more. Faster drying liquid screeds can therefore allow for the quicker installation of a floor covering.
However, there are a number of other factors which will affect drying times. While there are general and manufacturer guidelines, it is essential to take individual circumstances into account.
What factors impact the drying of screed?
One of the main factors affecting the drying times of the screed is the thickness of the installed screed, which is why liquid screeds installed at 40mm have faster drying times. Flowing screeds spread easily over large surface areas to form a smooth and level finish, drying faster and more evenly. Screed manufacturers are constantly innovating to improve this balance within their formulas.
Other external factors such as humidity levels, room temperature, and ventilation impact the overall drying process.
The moisture content in the air can significantly impact how quickly or slowly moisture evaporates from the surface of freshly laid screed. Higher humidity levels tend to slow down evaporation, which prolongs drying times. However, it’s worth noting that excessively dry air in the early life of a screed can cause rapid and uneven drying which may lead to cracking and reduced overall quality, so always refer to the manufacturer’s guidelines. Most require the screed to be protected from drafts in a weatherproof building for the first 2 to 7 days, and thereafter good air exchange is recommended.
High temperatures also accelerate the evaporation of moisture from the screed, leading to faster drying times. Conversely, low temperatures can prolong the drying process and potentially result in inadequate strength development.
Proper air circulation helps to remove excess moisture from the surface, allowing the screed to dry evenly and more quickly. By introducing fresh air into the environment, the use of ventilation aids will reduce humidity levels and aid drying after the initial early life curing of the screed (2–7 days dependent on the screed).
How do I check if screed is dry?
A visual inspection can give you a clue to whether or not screed is dry – look out for factors such as colour, texture and visible signs of dampness. However, for more precise readings, seek out an approved tool or method to test the moisture content of a screed.
One such tool, hygrometers measure humidity and can be mechanical or digital. Another method is a plastic sheet test, which involves placing a plastic sheet over an area of the screed and securing it tightly at all edges with tape. After leaving it for approximately 24 hours, inspect for condensation or wet patches under the sheet. Finally, in Calcium Bomb (CM) tests, calcium carbide granules react with remaining moisture in a sample of screed. The more gas that is produced from this reaction, the higher the pressure reading, indicating excessive moisture. These methods can determine whether further drying or remedial action should be taken before installing the floor covering.
How can I speed up the drying process of screed?
Optimising environmental conditions will help to speed up the drying process of screed. Firstly, ensuring adequate ventilation in the area after the initially curing period (2–7 days dependent on the screed), can greatly contribute to faster drying times. This can be achieved by opening windows or using fans and dehumidifiers to circulate air and remove excess moisture from the atmosphere in the room. Secondly, keep room temperatures ideally between 20–25 degrees Celsius if possible. This middle ground prevents higher temperatures from causing uneven drying and potential cracking as well as lower temperatures prolonging drying.
