What the CA grade on a Devizes specification means
Calcium sulphate screed has a binder made from calcium sulphate rather than cement, and it is designated under the European standard for screed materials. A typical entry reads CA-C25-F5: CA for calcium sulphate, then compressive strength (C) and flexural strength (F) in N/mm2.
For housing and apartments, three grades cover most needs. CA-C20-F4 covers lightly trodden rooms in a house. CA-C25-F5 is the workhorse for homes, flats and offices. Communal areas and other floors that see more footfall move up to CA-C30-F6. Your engineer or architect picks the grade, and that is the grade that turns up on the lorry.
Alpha hemihydrate products are named where speed or a reduced depth matters. They dry faster or can go thinner than a standard grade, but each follows its own product sheet, so the depth and drying rules come from the manufacturer.
The material sets with very little shrinkage. On an apartment floor that means large bays with few joints, and on a new build plot the ground floor can often be poured as one area. A few doorways and the edges of each heating zone still get joints, which we mark out ahead of pouring.
Only 7% of Devizes homes are from 2015 or later. New build plots of that kind, along with apartment floors, are where these grades usually appear on drawings. For background reading, see anhydrite screed explained.
Finishing Devizes calcium sulphate floors: laitance and moisture
Drying calcium sulphate throws up a fragile top crust known as laitance. Tile adhesive and levelling compound will not grip that crust dependably, so when the screed is dry enough we sand it back, vacuum up and prime. Only a calcium sulphate primer will do for that.
The moisture test catches plenty of people out. Calcium sulphate is often held to a tighter moisture figure than cement, and the hygrometer reading must meet the number in your flooring's data sheet rather than a rule of thumb. Where pipes run through the floor, putting the heating on from around day 7 usually hurries the drying along.
Keep calcium sulphate away from areas that may get wet. Since lasting damp weakens it, any floor that might flood or leak, from a wet room or walk-in shower to a utility room, is better in cement, either flowed or hand laid.
How the pump and hose reach the room is covered under pumped liquid screed in Devizes. For levelling a sanded floor before thin vinyl, see floor levelling in Devizes.
Anhydrite & Flow Screed prices in Devizes
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 Devizes
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 Devizes
Devizes is about 59.6 miles west-south-west of our Slough base as the crow flies, with postcodes including SN10. The nearest towns to it are Calne (6 miles), Melksham (6.3 miles), Chippenham (9 miles) and Trowbridge (9.5 miles).
More on anhydrite screed, part of our screeding services.
