What is screed laitance?

Screed laitance refers to the thin layer of weak and powdery material that can form on the surface of floor screed during the drying and curing process and is particularly prevalent with anhydrite screed. Anhydrite screed is a type of calcium sulphate-based screed that is commonly used in construction projects.

During the installation and drying of anhydrite screed, excess moisture can rise to the surface and react with the calcium sulphate to form a thin layer of calcium carbonate, which is the primary component of anhydrite screed laitance. This layer can weaken the bond between the floor and any subsequent layers, such as coatings or adhesives, and can create a rough, uneven surface that is unsuitable for further finishing.

To remove screed laitance, a sanding machine with a coarse grit sandpaper or diamond abrasives can be used to grind away the surface layer of the floor. It is important to use appropriate tools and techniques for surface preparation before applying any coatings or finishes. Following the manufacturer's instructions for installation, curing and surface preparation is critical for minimising the formation of screed laitance and ensuring a durable and long-lasting floor.