Specifying calcium sulphate for Northfleet apartment floors
Anhydrite is the everyday name for calcium sulphate screed, and on a drawing it appears as a code set by the European standard for screeds. The code carries two strengths, both in N/mm2, with the C figure compressive and the F figure flexural. Most buildings need one of three grades. A home with only light traffic can use CA-C20-F4. Apartments, offices and the majority of homes take CA-C25-F5. Floors expected to work harder get CA-C30-F6.
For a block of flats or a run of new plots, the engineer's specification sets the grade, and that exact grade goes in, with no near equivalent swapped for it. Now and then a specification asks for an alpha hemihydrate material instead. Designers pick these when the floor has to dry sooner or be shallower, and since each has its own data sheet setting depth and drying, that sheet is what we follow.
The material has one big advantage for flats: it hardly shrinks. Bays can therefore be big and joints few, and a complete flat is often filled in a single pour. Doorways and the boundaries between heating zones may still need a joint, and we mark out the bays and joints in advance.
New schemes such as Cable Wharf, with houses and apartments built together, are the kind of project where a calcium sulphate grade can appear on the drawings, and where every plot should be poured to the same grade and depth. There is more on how the material dries and moves in our explainer on calcium sulphate screed.
Laitance, primers and moisture limits in Northfleet
Pouring the screed is half the job. While the floor dries, a fine, weak crust known as laitance forms on top. Adhesive laid over it grips the skin, not the screed, and the floor can fail later. When the floor has dried far enough, we sand that crust away, and the bare surface gets a primer designed for calcium sulphate.
Then comes the moisture reading. Flooring makers often allow less moisture in calcium sulphate than in a cement screed, which means a reading fine for tiling over sand and cement can fail on anhydrite. A hygrometer, not a count of days, tells us where it stands. Where a Northfleet flat has heating pipes in the floor, running them from about day 7 is normally allowed as a way to force dry it.
One place anhydrite should not go is anywhere that may stay wet. Bathrooms with level showers, utility rooms and plant areas are better on cement based flowing screed or a hand-laid sand and cement floor. Where an old base must be cleaned or ground before any new screed, our floor preparation service comes first. About 2.9 miles away, we also pour anhydrite screed in Grays.
Anhydrite & Flow Screed prices in Northfleet
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 Northfleet
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 Northfleet
Northfleet is about 43.3 miles east of our Slough base as the crow flies, with postcodes including DA11. The nearest towns to it are Gravesend (1 miles), Tilbury (1.7 miles), Swanscombe (2.8 miles) and Grays (2.9 miles).
More on anhydrite screed, part of our screeding services.
