What the anhydrite grade on a Didcot drawing means
Every calcium sulphate screed on a drawing carries a short code. CA means calcium sulphate. Following that, C gives compressive and F flexural strength, each in N/mm2, as set by the European screed standard.
CA-C20-F4: a lightly used domestic floor.
CA-C25-F5: the general grade for houses, flats and offices.
CA-C30-F6: floors that will take harder wear.
The grade is set by whoever wrote the specification, and we pour to it. Where a product sheet names an alpha hemihydrate screed instead, the job follows that sheet for depth, drying and heat-up. Designers pick them when the floor has to dry sooner or be laid thinner.
The material's defining trait is low shrinkage. It barely moves as it cures, so large bays can be poured with few joints. On an apartment floor that means a whole flat can often be done in one pour. Joints still go at door thresholds and between heating zones where needed, and the layout is set before we start.
In 2015 Didcot became the first existing town to be given garden town status, and 23% of its homes were built in 2015 or later. Newer housing and apartment blocks are where a CA grade is most likely to appear on the drawings.
One restriction is absolute. Water damages calcium sulphate, so any floor likely to get wet should have a cement based flowing screed or a hand-laid Didcot cement screed. Our plain guide to anhydrite goes further into the material.
Sanding, testing and priming Didcot anhydrite floors
Pouring the screed is half the job. The other half happens before the floor covering goes down.
The surface first. While calcium sulphate settles, a soft film called laitance gathers on its surface. It has to be removed, because adhesive and levelling compound bond poorly to it. When the floor has dried enough, we sand that film off down to firm screed and vacuum away the dust. If a builder wants that done as a separate stage, it comes under our floor preparation service.
Then the moisture. Flooring makers often allow calcium sulphate less moisture than a cement screed. The floor is tested with a hygrometer to measure relative humidity, and the reading is compared with the limit your flooring maker states. From about 7 days, calcium sulphate can usually be force dried with underfloor heating, which brings that reading down sooner. How moisture leaves a screed is covered in our article on drying times.
Then the primer. Only a primer compatible with calcium sulphate should go on before adhesive or compound.
You get written advice on drying and laitance to give the flooring fitter. About 10 miles away, we also cover Oxford calcium sulphate screeding.
Anhydrite & Flow Screed prices in Didcot
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 Didcot
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 Didcot
On the map, Didcot sits west of Slough, about 26.2 miles from our base in a straight line (postcodes including OX11), next to Abingdon-on-Thames (4.7 miles), Wantage (8 miles), Oxford (10.1 miles) and Thatcham (14.1 miles).
More on anhydrite screed, part of our screeding services.