Reading an anhydrite specification for Grays South flats
A specification for calcium sulphate screed normally names a grade in the form CA-C25-F5. CA means calcium sulphate. After the C comes the compressive strength and after the F the flexural strength, measured in N/mm2.
CA-C20-F4 suits the rooms in an ordinary house that only see light use.
Most homes, flats and offices are poured in CA-C25-F5.
CA-C30-F6 takes heavier traffic, communal corridors or commercial ground floors for instance.
The Grays South project plans new homes and commercial space in the town centre, and apartment floors of that kind are exactly where a grade is set by the designer and we pour to it. A tight programme or a thin floor can push the designer towards an alpha hemihydrate product, and its depth and drying then come from its own data sheet.
The reason specifiers pick calcium sulphate is low shrinkage. Big bays go down with few joints or none, and we mark out where bays and joints go before pour day. In a Grays flat it is often laid on an acoustic layer, and our own team prepares the full build-up.
The material is not the right choice everywhere. Anywhere that might get wet takes a cement based flowing screed instead. How the material behaves is explained in anhydrite screed explained.
Sanding, priming and moisture tests in Grays
Two steps separate a calcium sulphate floor that performs from one that causes trouble later: removing the laitance and testing the moisture.
As the screed sets, a thin and weak film called laitance forms on top. Once dry, that skin is sanded back, the dust vacuumed, and a calcium sulphate compatible primer brushed on. Stick flooring to laitance and the adhesive may let go. Sanding and priming can be done by us through floor preparation.
Moisture is the other. Tile, LVT and wood makers often set a tighter moisture figure for calcium sulphate than for a cement base, so it has further to dry. The hygrometer tells us when it is there. On a heated apartment floor, running the underfloor heating from about day 7 normally force dries it.
We leave drying and laitance advice in writing so the flooring contractor starts on a floor in a known state, with the grade and the date of the pour recorded alongside it. The same service in Dartford is on our anhydrite screed in Dartford page.
Anhydrite & Flow Screed prices in Grays
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 Grays
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 Grays
As the crow flies, our yard in Slough is about 42 miles from Grays, which lies to the east. Postcodes here include RM17 and RM18, and Tilbury (2 miles), Swanscombe (2.6 miles), Northfleet (2.9 miles) and Gravesend (3.2 miles) are close by.
More on anhydrite screed, part of our screeding services.
