Reading the CA grade on a Woking specification
Anhydrite screed is a calcium sulphate material, not a cement one. It is graded under a British and European standard, and the letters on a drawing tell you what it must do. Read CA-C25-F5 as two numbers: 25 is compressive strength and 5 is flexural strength, both measured in N/mm2.
For a house floor with light traffic, CA-C20-F4 is enough. The middle grade, CA-C25-F5, is what a typical house, flat or office gets, and floors that take a heavier pounding move up to CA-C30-F6. Alpha hemihydrate screeds sit outside that scale: they are picked for quicker drying or thinner sections, and their own data sheet, not the general guidance, governs how they are laid.
With so little shrinkage, big bays can be poured with hardly any joints. On an apartment floor or a terrace of new build plots, we plan the bay and joint layout before the pour, around door thresholds and any movement joints in the structure.
New building is a steady part of Woking's housing. 11% of its homes were built between 2000 and 2014, and the Sheerwater regeneration adds new homes on the old athletics track site. A cement based flowing screed is the alternative wherever the floor may get wet, such as a plant room or bathroom without full tanking, because calcium sulphate does not tolerate repeated wetting. Our plain English guide to anhydrite covers the material in more depth.
Laitance and moisture tests before flooring in Woking
Two steps separate a calcium sulphate floor that performs from one that fails under the finish.
The first is laitance. As the screed settles, a weak, fine layer forms on top. Stick a floor finish to it and the adhesive holds only as well as that thin crust does. When the floor has dried far enough, we sand the crust away, clear the dust and apply a primer designed for calcium sulphate, which closes the surface and leaves the adhesive something firm to hold. Sanding and priming are both part of our floor preparation work.
The second is moisture. Plenty of flooring makers allow less moisture in a calcium sulphate base than in a cement one, which means the usual cement screed figure may be the wrong number to aim for. The way to know is a hygrometer reading compared with the limit on the flooring maker's data sheet. On a heated plot, running the heating from about 7 days can push the drying along and cut the wait.
How the drying time is worked out is in our guide to screed drying. The same specification work applies in Chertsey.
Anhydrite & Flow Screed prices in Woking
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 Woking
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 Woking
As the crow flies, our yard in Slough is about 15.2 miles from Woking, which lies to the south-south-east. Postcodes here include GU21, GU23 and GU22, and Addlestone (4.6 miles), Guildford (5.5 miles), Chertsey (5.6 miles) and Weybridge (5.7 miles) are close by.
More on anhydrite screed, part of our screeding services.
