Reading the anhydrite grade on a Horley specification
A calcium sulphate specification usually names a designation from the European standard for screed materials. Read it as two figures in N/mm2: after the C comes compressive strength, after the F flexural strength. On a lightly used domestic floor, CA-C20-F4 is enough. The middle grade, CA-C25-F5, is what the majority of houses, flats and offices get. Communal corridors in a Horley block and commercial ground floors take harder wear, which is where CA-C30-F6 comes in.
Alpha hemihydrate screeds sit outside that scale; they get picked when a floor has to dry sooner or be laid thinner. They follow their own product sheet for depth and drying, so the numbers on the data sheet, not a general rule, decide the pour.
What makes calcium sulphate useful in blocks of flats is its low shrinkage. Large bays can be poured with fewer joints than a cement screed would need, which keeps the surface continuous under sheet vinyl or long runs of LVT. Where the bays and joints fall gets decided ahead of pour day, with doorways and changes of heating zone looked at first.
Water is its weakness, so keep it out of any room where the floor could get wet. In a Horley flat, that means the walk-in shower, the wet room and possibly the utility room should instead get a flowing screed with a cement base, or hand-laid sand and cement. On a mixed specification, we pour each material in its own area.
For the background on this material, our anhydrite screed explained guide covers how it differs from cement screeds.
Laitance, primers and moisture tests in Horley
Census figures date 11% of Horley's homes to 2000 to 2014, and flat floors and new build plots from that kind of period are the usual place to find calcium sulphate written into the drawings. Whatever the building, the same sequence follows the pour.
While it dries, a calcium sulphate floor grows a thin, weak skin on its surface, known as laitance. It must come off. When the screed has dried enough, we sand that skin away down to firm material and vacuum up the dust, a step that belongs to proper preparation of the floor. Leave it in place and the adhesive or levelling compound on top may let go.
Next comes the moisture test. The moisture reading a flooring maker will accept is often lower for calcium sulphate than for cement, so a number that would pass on sand and cement can still fail here. We measure it with a hygrometer instead of going by the calendar. In a heated flat or house, the system can normally help dry the screed from around day 7.
The last step is a primer made to suit calcium sulphate. Cement based adhesives can react with the screed without the right primer. Nearby, our anhydrite flow screed in East Grinstead page covers the same material.
Anhydrite & Flow Screed prices in Horley
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 Horley
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 Horley
As the crow flies, our yard in Slough is about 32.5 miles from Horley, which lies to the south-east. Postcodes here include RH6, and Crawley (4.1 miles), Redhill (4.8 miles), Reigate (4.9 miles) and East Grinstead (7.5 miles) are close by.
More on anhydrite screed, part of our screeding services.
