What Is Anhydrite Screed & When Should You Use It?
Anhydrite screed has become one of the most widely used flooring solutions in modern construction, and for good reason.
Its flow characteristics, speed of installation and compatibility with underfloor heating systems make it a practical and increasingly popular alternative to traditional sand cement screed for a wide range of project types.
Here is what you need to know about anhydrite screed and when it is the right choice for your project.
What Is Anhydrite Screed?
Anhydrite screed, also known as calcium sulphate screed or liquid flow screed, is a flowing screed made from calcium sulphate binder mixed with sand and water.
Unlike traditional sand cement screed, which must be mixed on site and spread by hand, anhydrite screed is produced in liquid form and pumped directly into position, where it flows and self-levels across the floor area.
The result is a consistently flat, smooth surface that requires far less labour to install than a hand-applied screed and is considerably more forgiving over large or complex floor areas where achieving a level finish manually would be difficult and time-consuming.
How Is Anhydrite Screed Different From Traditional Screed?
Application Method
Traditional sand cement screed is a semi-dry mix that is spread and levelled by hand using screeding bars and floats. It requires a high degree of skill to achieve a consistently flat finish, particularly over large areas.
Anhydrite screed, by contrast, is pumped through hoses and flows into place, self-levelling as it goes. This makes installation significantly faster and reduces the reliance on manual finishing.
Drying Time
One of the most notable differences between the two materials is drying time. Traditional sand cement screed typically takes around one day per millimetre of depth to dry sufficiently for foot traffic, meaning a standard 75mm screed could take ten weeks or more to reach the moisture content required for floor coverings.
Anhydrite screed dries more quickly in the early stages, though it does require forced drying using heating and ventilation before floor coverings can be applied.
Flatness & Consistency
Because anhydrite screed flows and self-levels, it tends to produce a flatter and more consistent surface than hand-applied sand cement screed. This is particularly beneficial where tight tolerances are required for the finished floor covering, or where large areas need to be covered efficiently without compromising quality.
When Is Anhydrite Screed The Right Choice?
Projects With Underfloor Heating
Anhydrite screed is particularly well suited to projects incorporating wet underfloor heating systems. Its flowing nature means it encapsulates the pipework fully and makes direct contact with the pipes on all sides, resulting in excellent thermal conductivity and more efficient heat transfer than a hand-applied screed can typically achieve.
This improves the overall performance of the heating system and can reduce running costs over time.
Large Floor Areas
For commercial, industrial and large residential projects where significant floor areas need to be screeded quickly, anhydrite screed offers a clear advantage.
A skilled team using pump-applied anhydrite screed can cover considerably more floor area in a single day than would be possible with traditional methods, making it the preferred choice where programme deadlines are a priority.
New Build & Refurbishment Projects
Anhydrite screed is widely used in new build residential and commercial developments, as well as refurbishment and conversion projects where speed and quality of finish are equally important.
Its self-levelling properties make it particularly useful in conversions where the existing substrate may be uneven or where multiple floor levels need to be brought to a consistent height.
Are There Any Limitations To Be Aware Of?
Anhydrite screed is not suitable for use in areas that will be exposed to standing water or consistently high levels of moisture, such as wet rooms or external applications.
It also requires a laitance removal process before floor coverings are applied, which involves light sanding or grinding of the surface to open the pores and achieve a good bond with adhesives.
These are straightforward considerations that an experienced screeding contractor will factor into the project specification from the outset.
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