Specifying anhydrite for Crawley flats and new plots
Calcium sulphate screeds are graded by compressive and flexural strength in N/mm2, written as a designation such as CA-C25-F5. The C figure is compressive strength, the F figure flexural. Light domestic use is covered by CA-C20-F4. CA-C25-F5 is the workhorse grade for houses, apartments and offices. For heavier wear the specification moves up to CA-C30-F6. On a new plot the grade comes from the design team, and we pour the product named rather than a substitute.
An alpha hemihydrate product is sometimes named instead, where the programme is tight or the section has to be thin. Every such product has a data sheet giving its drying time and minimum depth, and we pour to it.
What calcium sulphate does well is stay put as it sets. It barely shrinks, so wide bays need few joints, a good fit for a block of flats or a new house with an open-plan ground floor. Joints are still planned before the pour, at door thresholds and between heating zones, so the layout matches the building.
In flats, acoustic performance between floors matters. The anhydrite screed usually floats over insulation or a resilient layer, separated from the walls by an edge strip, so it does not carry sound into the structure. Getting that build-up right before the pour matters more than the grade. Homes built more recently at Forge Wood stand a better chance of already having flowing screed over their heating. Our anhydrite explainer covers the material in more detail.
Preparing Crawley anhydrite floors for their finish
Pouring is half the job. A thin, weak crust called laitance forms on calcium sulphate while it dries. If flooring adhesive goes onto it, the floor is only as strong as that skin. Once the floor has dried far enough, that crust is sanded off and a primer suited to calcium sulphate is rolled on.
Moisture testing comes next. Flooring makers often set the moisture bar lower for calcium sulphate, so a reading that would let a tiler start on cement screed may still rule out an anhydrite floor. We test with a hygrometer. Where the house has underfloor heating, the system can normally help force dry the screed from about day 7.
Anywhere that could stay wet is the wrong place for calcium sulphate. Bathrooms with walk-in showers, utility rooms and commercial wash areas need a cement based flowing screed or sand and cement screed in wet rooms. Offices, such as those in Manor Royal, are a common use for the CA-C25-F5 grade, while warehouse floors there are a job for high strength screed instead.
Anhydrite & Flow Screed prices in Crawley
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 Crawley
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 Crawley
Crawley is about 35 miles south-east of our Slough base as the crow flies, with postcodes including RH10 and RH11. The nearest towns to it are Horley (4.1 miles), Horsham (7.1 miles), East Grinstead (7.9 miles) and Reigate (8.5 miles).
More on anhydrite screed, part of our screeding services.
