Specifying anhydrite grades for Egham flats and new builds
Each calcium sulphate screed carries a coded designation from the European standard for screeds, and plans for a new Egham house or block of flats normally state it. Read the C figure as compressive strength, with F standing for flexural strength, with both given in N/mm2.
Light domestic traffic is what CA-C20-F4 is meant for. A typical flat or house gets CA-C25-F5, which is the general grade used in houses, apartments and offices. CA-C30-F6 is used where floors will take heavier use. We pour the grade the engineer has set and do not swap it for something else.
Now and then the drawings name an alpha hemihydrate screed. Those are picked to save drying time or depth, and every one has its own data sheet setting how thin it can go and how long it takes to dry. On a tight programme for an apartment block, that can bring the flooring date forward.
Purpose-built blocks hold 19% of Egham's homes. For those floors, calcium sulphate offers a real advantage: it shrinks very little, so large bays can be poured with few joints, and a flat's whole floor can go down in one visit. Joints are still planned in advance at door thresholds and between heating zones.
Before the pour, the full build-up is prepared by our own team, including insulation, edge strip and membrane. More background is in what anhydrite screed is.
Laitance, moisture tests and wet areas in Egham
Calcium sulphate forms a thin, weak surface skin as it dries, known as laitance. Leave it on and whatever goes over it, adhesive, primer or levelling compound, is stuck to a skin that can come away, so it is sanded off first. A primer designed for calcium sulphate then goes on the sanded surface.
Then comes the moisture test, and the bar is set higher than most people assume. Plenty of flooring makers allow less moisture in calcium sulphate than in cement, so a hygrometer figure that would be fine on a sand and cement floor can be a fail on anhydrite. With underfloor heating in place, the screed can usually be force dried from about 7 days, which is the quickest way to reach the limit.
Where the material should not go is anywhere that may get wet. So in student buildings and new Egham blocks, showers, wet rooms and a few utility spaces should be poured with a flowing screed that is cement based, or hand-laid cement screed for those Egham wet areas. Using both types on one project is normal.
The same material and grades are poured in nearby Chertsey.
Anhydrite & Flow Screed prices in Egham
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 Egham
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 Egham
Egham is about 8.1 miles south-south-east of our Slough base as the crow flies, with postcodes including TW20, TW18 and GU25. The nearest towns to it are Staines-upon-Thames (1.6 miles), Chertsey (3.4 miles), Ashford (3.8 miles) and Windsor (4.3 miles).
More on anhydrite screed, part of our screeding services.