Choosing an anhydrite grade for Witham plots
Look at the floor notes for a new Witham house and you may see CA-C25-F5. Read it in parts: CA for calcium sulphate, then C25 for how much load it takes when squeezed and F5 for how well it resists bending, both given in N/mm2. On a lightly used house floor, CA-C20-F4 is enough. The middle grade, CA-C25-F5, is what most domestic, flat and office floors take, with CA-C30-F6 reserved for heavier wear.
We do not choose the grade on a housing plot. The engineer writes it into the specification, and that is what goes in the pump. Now and then the drawings ask for an alpha hemihydrate mix in its place, because the programme is tight or the floor has to be shallower. Then the maker's own sheet fixes how deep it goes and how long it dries, and we keep to it.
Developers pick calcium sulphate for practical reasons. Shrinkage while curing is slight, which means wide bays with hardly any joints, and the mix closes in tightly around heating pipes. Where a joint is unavoidable, at a door threshold for instance or between two heating zones, its line is agreed before the pour.
Flats make up 19% of Witham's homes, and apartment floors are a natural fit for calcium sulphate: a large area poured in one visit over an acoustic or insulation layer. For how anhydrite compares with cement screeds, read our plain account of anhydrite.
Laitance and moisture on Witham anhydrite floors
With 22% of Witham homes built since 2000, a good many floors in town are young. On any of them laid in calcium sulphate, the laitance must come off before the flooring goes on. That is the thin, weak crust left on top as the screed dries out. Adhesive will not stick to that crust, so once the screed has dried sufficiently we sand it off and prime what is underneath using a primer designed for calcium sulphate.
Dryness is the second check. Manufacturers of floor coverings commonly set a lower moisture limit for calcium sulphate than for cement, so a reading a cement floor would pass can still be too high here. A hygrometer settles it, not a count of weeks. If heating pipes run through the floor, switching them on from about 7 days normally speeds things up.
Keep anhydrite away from water. Where a Witham bathroom becomes a wet room or gets a walk-in shower, we switch to a cement based flowing mix, or to hand-laid sand and cement in Witham. If the flooring needs a perfectly smooth base after sanding, floor levelling can follow.
Anhydrite & Flow Screed prices in Witham
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 Witham
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 Witham
On the map, Witham sits east-north-east of Slough, about 58.3 miles from our base in a straight line (postcodes including CM8), next to Maldon (5 miles), Braintree (6.6 miles), Chelmsford (8.4 miles) and Halstead (10 miles).
More on anhydrite screed, part of our screeding services.