Reading the screed specification for Sevenoaks projects
Anhydrite is just the trade name people use for calcium sulphate screed, and its code follows the European screed standard: the C part is compressive strength and the F part flexural strength, both in N/mm2. On a Sevenoaks plan you will usually meet one of three: CA-C20-F4 if a domestic floor sees little traffic, CA-C25-F5, which covers most houses, flats and offices, or CA-C30-F6 when the floor has to work harder. When an architect or developer names a grade, that is what we supply; when nothing is named, we recommend one for the use of the floor.
Alpha hemihydrate screeds are a different family, picked when quicker drying or a thinner layer is needed, for instance a Sevenoaks basement with little headroom to spare, and the depth and drying rules then come from the maker's sheet for that product.
Specifications of this kind mostly come with apartment floors and new build plots. Flats in purpose-built blocks account for 16% of Sevenoaks households. Homes from 2015 onwards are only 6% of the Sevenoaks total, yet plots of that age tend to be drawn around a flowing screed. The low shrinkage of calcium sulphate allows large bays with few joints, so an open-plan apartment floor can often be poured without the joint lines a cement screed would need. Before pumping starts, we decide where each bay ends and each joint runs.
How the material is pumped into a Sevenoaks home sits on the Sevenoaks liquid screed page. More on what the material is made of is in anhydrite screed explained.
Laitance, moisture and primers before Sevenoaks flooring
Laitance is the thin, weak skin left on top of calcium sulphate as it dries. It is sanded away once the screed is dry, and only then can adhesive or a covering go on. Left in place, it can cause tiles or timber to debond.
With this material the moisture test carries extra weight. Many flooring brands set a stricter moisture ceiling for calcium sulphate than for cement, so an anhydrite floor can still be too damp at a reading a cement screed would pass. A hygrometer gives the real reading. On a heated Sevenoaks floor, the pipes can usually help dry the screed from about 7 days onward, as long as the system's heat-up schedule is followed.
Next comes a coat of primer chosen to suit calcium sulphate, applied to the dry, sanded surface. The primer has to suit the adhesive system as well as the screed, so we check both before handing over, along with written drying and laitance advice.
There is one place calcium sulphate should not go: floors that may get wet. So keep it out of wet rooms, plant rooms and any floor where water might pool; there, a cement based flowing screed or hand-compacted sand and cement does the job. If an existing anhydrite floor needs attention, our floor preparation service covers sanding and priming.
Anhydrite & Flow Screed prices in Sevenoaks
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 Sevenoaks
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 Sevenoaks
Sevenoaks is about 40.4 miles east-south-east of our Slough base as the crow flies, with postcodes including TN13 and TN15. The nearest towns to it are Tonbridge (6.4 miles), Oxted (8.5 miles), Swanley (8.8 miles) and Bromley (9.6 miles).
More on anhydrite screed, part of our screeding services.