Specifying calcium sulphate screed for Corsham plots
Every calcium sulphate screed is given a code under the European screed materials standard, for example CA-C25-F5. CA marks the binder. The number after C is compressive strength and the one after F is flexural strength, each in N/mm2. Three grades cover most building work. CA-C20-F4 is enough for a home's quieter rooms with light foot traffic. For houses, flats and offices in general, the usual call is CA-C25-F5. Where floors face heavier wear, CA-C30-F6 is the one to ask for.
Outside the CA grades, a spec can also name an alpha hemihydrate product. Designers turn to them when drying time or depth is the problem, say on a plot with a tight handover or a refurbishment short on height. Every one comes with a data sheet setting how thin it can go and how it dries, and we follow it to the letter.
As it sets, calcium sulphate hardly shrinks at all. That allows large bays with few joints, so an open kitchen and living area on a new plot, or a run of apartment floors, can be poured without joints cutting across the room. Some thresholds and the line between two heating zones still want a joint, and those are marked on a bay plan before we pour.
Flats make up 13% of Corsham's homes, and apartment floors are one of the places this material is specified, most often at CA-C25-F5. For the background, see our anhydrite screed explainer.
After the pour: Corsham laitance, primers and testing
Two steps separate a good calcium sulphate floor from a failed one, and both happen after the pour.
The first is laitance. As the screed dries, a weak, powdery skin forms on top. It must be sanded off once the floor is dry enough, otherwise adhesive bonds to the skin and the finish lifts later. Next comes priming, with a product made to bond to calcium sulphate; a cement primer is the wrong tool here.
The second is moisture. Floor covering manufacturers are often stricter about moisture in calcium sulphate than in cement screed. We test with a hygrometer and report the reading in writing, along with drying and laitance advice. Got underfloor heating? Switching it on from about day 7 helps pull the moisture out and shortens the wait.
There are also rooms where this screed does not belong. Calcium sulphate goes soft with long exposure to water, so showers and wet rooms take a cement flowing screed instead.
If you are comparing systems for a heated floor, see our underfloor heating screed page for Corsham.
Anhydrite & Flow Screed prices in Corsham
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 Corsham
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 Corsham
Corsham is about 66.8 miles west of our Slough base as the crow flies, with postcodes including SN13. The nearest towns to it are Chippenham (3.5 miles), Melksham (4.7 miles), Calne (7.8 miles) and Trowbridge (7.9 miles).
More on anhydrite screed, part of our screeding services.
