What Royston specifications mean by CA grades
Under the European standard for screed materials, every calcium sulphate screed is given a designation code. Two numbers sit in that code, both in N/mm2: C for how much crushing load it takes and F for how much bending. A lightly trodden bedroom floor in a Royston house manages with CA-C20-F4. Royston houses, flats and offices mostly get CA-C25-F5, the everyday choice. CA-C30-F6 is held back for heavier use.
On a new housing phase the developer's engineer chooses the grade and we pour what the drawings show. On refurbishments, where nobody has set one, we suggest a grade from how the room is used and the floor finish planned. Occasionally an engineer wants an alpha hemihydrate binder, normally to save time or depth, and then its maker's data sheet governs depth and drying for us.
What makes the material practical is that it shrinks very little. Big open bays can go down with few joints, ideal for open-plan ground floors and flats. Purpose-built flats are 18% of Royston's homes, and apartment floors are one place calcium sulphate gets specified. We set out bays and joints before the pour and prepare the build-up with our own crew.
Rooms on a plot or in a block that may get wet need a different screed, explained below. For the material in more depth, including why it is often chosen over heating, read anhydrite screed explained.
Before flooring goes down on a Royston anhydrite floor
Anhydrite leaves a powdery crust on top as it cures, and the trade calls it laitance. Adhesive and levelling compound stick to that layer instead of the screed, so it gets sanded off when the floor is dry enough. Priming comes next, using a product suited to calcium sulphate, and only then can glue or compound follow.
Then the moisture test. Flooring makers tend to be stricter about anhydrite, so a Royston floor reading acceptable for cement may still be judged too damp. We read it with a hygrometer, not the calendar. Where loops run under the floor, they can usually be used gently from about day 7 to hurry the drying.
Wet areas are off limits. On a new Royston plot that rules out the en-suite with its walk-in shower, any wet room, and a utility where a leak could happen; those take a cement based flowing screed or sand and cement in wet rooms. If the finished floor needs smoothing for thin flooring, see levelling compound over anhydrite. Not far away, there is a separate page on anhydrite flow screed in Stevenage.
Anhydrite & Flow Screed prices in Royston
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 Royston
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 Royston
On the map, Royston sits north-east of Slough, about 44.6 miles from our base in a straight line (postcodes including SG8), next to Baldock (8.3 miles), Stotfold (9.3 miles), Letchworth (10.2 miles) and Biggleswade (10.7 miles).
More on anhydrite screed, part of our screeding services.