Choosing a calcium sulphate grade for Windsor flats
On a specification, calcium sulphate screed carries a code in three parts. CA says it is calcium sulphate. The C and F parts give the compressive and flexural strengths in N/mm2, as set by the European screed materials standard.
Three grades cover most buildings. Rooms in a home that see light use can have CA-C20-F4. For the bulk of homes, flats and offices, the grade to expect is CA-C25-F5. Floors that will take more wear get CA-C30-F6. On a specified project we pour the grade written on the drawings rather than a near equivalent.
Sometimes the drawings swap in an alpha hemihydrate product. Those are picked when quicker drying or a slimmer floor is needed, and each has its own data sheet setting depth and drying, which is what we follow.
The practical appeal is low shrinkage. A calcium sulphate screed can be poured in large bays with few joints, so a whole flat, or a whole floor of a block, can be done in one visit with joints planned only where they are needed, such as at thresholds and between heating zones.
New building is a small share of Windsor, with 4% of homes built since 2015, so a calcium sulphate floor here is as likely to go into a conversion or refurbishment as a new block, and the drawings are worth reading closely. Our guide to anhydrite screed explained walks through a typical specification.
Sanding, testing and priming anhydrite in Windsor
As calcium sulphate dries, its surface forms a thin, weak skin, which is the laitance. That skin has to be sanded away before adhesive or compound goes on, or the flooring is only held by the crust. The sanded floor then gets a primer that is suited to calcium sulphate.
Moisture is the other test. Flooring makers often allow less moisture in calcium sulphate than in cement, so the floor needs a hygrometer test before anything goes down, not a guess based on how many weeks have passed. If the flat has heating fitted, switching it on from about 7 days usually speeds the drying.
Wet areas are the exception for calcium sulphate. Wet rooms, any floor that could stay damp and bathrooms that have a walk-in shower need a flowing screed based on cement. In a block where most of the floor is anhydrite, those rooms can be poured separately in a cement based material.
If the screed needs a smoother finish after sanding for sheet vinyl or LVT, levelling compound over anhydrite is primed and applied to suit the base. Specified work in Staines-upon-Thames is covered under anhydrite flow screed in Staines-upon-Thames.
Anhydrite & Flow Screed prices in Windsor
Liquid flowing screed (which includes anhydrite): £24 to £31 per m² supplied and laid (MyJobQuote, August 2026), so £960 to £1,240 for 40 m². MyJobQuote does not say whether these figures include VAT. See our floor screeding cost guide or screed calculator.
Who lays your anhydrite and flow screed in Windsor
K & B Screeding’s own team, led by director Donatas Bardisevicius. Founded 2019, company 12298780.
See what customers say in our Google reviews and on our testimonials page.
Anhydrite & Flow Screed from Slough to Windsor
Windsor is about 3.9 miles south-south-east of our Slough base as the crow flies, with postcodes including SL4 and TW19. The nearest towns to it are Slough (2.1 miles), Egham (4.3 miles), Staines-upon-Thames (5.3 miles) and Maidenhead (5.6 miles).
More on anhydrite screed, part of our screeding services.
