CA grades on Chippenham drawings explained
Most people still say anhydrite, but on paper calcium sulphate screed is identified by a code from the European screed materials standard. The C number gives crushing (compressive) strength; the F number, bending (flexural) strength; both are in N/mm2. Expect one of three codes on a Chippenham drawing: CA-C20-F4, meant for lightly used domestic floors; CA-C25-F5, the usual grade for houses, flats and offices; and CA-C30-F6 for floors that take a harder pounding.
Now and then the spec calls for an alpha hemihydrate screed in place of a CA grade. They get picked for faster drying or a slimmer section, and as each brand publishes its own depth and drying rules, we follow that brand's sheet. Swapping one product for another without the engineer's agreement is not something we do.
The material's main structural advantage is low shrinkage. It can be poured in large bays with few joints, which suits a run of apartment floors or a new build ground floor with an open kitchen and living space. Some doorways and the boundaries between heating zones still need a joint, so we set out bays and joints on the plan before the pour instead of sawing them in later.
Homes completed since 2015 make up 8% of Chippenham's housing, and recent plots like these are where the grades above tend to appear on drawings. If you want the background first, our guide to anhydrite screed explained covers how the material works.
Laitance, primers and moisture limits for Chippenham floors
As calcium sulphate dries, a soft, weak film called laitance rises to the top. Leave it in place and adhesives grip the skin rather than the screed, which is how tiles and LVT come loose months later. Once drying allows, we sand that film off and prime with a product meant for calcium sulphate. Putting a cement primer down in its place is asking for trouble.
Testing comes next. The moisture bar is often set lower for calcium sulphate, so a number that would pass on a sand and cement floor in a Chippenham terrace can fail on a new flat. A hygrometer test is done before we hand the floor on to your flooring fitter. In a heated floor, the system can usually help drive the moisture out from about 7 days onward.
There is one clear limit on where the material goes. Keep it out of anywhere water could sit: wet rooms, walk-in showers and utility rooms prone to leaks. Those rooms are better poured with a flowing screed made from cement, or laid by hand as a traditional sand and cement floor.
If laitance was never removed on an existing floor and a new finish has failed, our floor preparation service can strip it back before relaying.
Anhydrite & Flow Screed prices in Chippenham
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 Chippenham
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 Chippenham
On the map, Chippenham sits west of Slough, about 63.6 miles from our base in a straight line (postcodes including SN15), next to Corsham (3.5 miles), Calne (4.9 miles), Melksham (6 miles) and Devizes (9 miles).
More on anhydrite screed, part of our screeding services.
