Calcium sulphate grades for Selsey new builds
Every calcium sulphate screed carries a code set by the European screed standard. In that code, C gives compressive strength and F gives flexural strength, each in N/mm2. Three grades cover most housing work.
For a lightly used domestic floor, CA-C20-F4 is enough. Most houses, flats and offices take CA-C25-F5. Where the floor will work harder, CA-C30-F6 is the step up. On a new Selsey plot, the designer or engineer picks the grade and we lay exactly that.
Now and then the drawings call for an alpha hemihydrate screed. Designers pick it when the floor must dry sooner or be thinner, such as a retrofit with only a little height over the pipes. Its depth and drying time are taken from the maker's product sheet, not from the usual rules of thumb.
Because it barely shrinks while setting, we can pour big bays with hardly any joints, a good fit for an open-plan ground floor or a wide extension. Some joints are still needed, for instance at door thresholds or where one heating zone meets another, and we settle the bay layout with you before pouring.
If you are weighing up whether calcium sulphate is right for the job at all, our guide to anhydrite screed explained covers the background. For a bungalow being fully rebuilt, the same grades apply as on a new plot, but the existing floor height usually decides the depth.
Sea air, laitance and moisture testing in Selsey
Calcium sulphate needs looking after once it is down. While it dries, the surface grows a thin, weak skin known as laitance. Sand that off before adhesive or levelling compound touches it, or the new floor ends up stuck to a crust rather than the screed itself. The sanded floor then gets a primer designed for calcium sulphate.
Moisture testing is the step that catches people out. Plenty of flooring makers allow less moisture in calcium sulphate than in cement. So a reading that would pass for tiling on a cement screed can still fail on anhydrite. In a coastal town, where damp air slows drying, a hygrometer reading is the only safe guide. From around 7 days, the underfloor heating can normally be run to push the drying along.
One rule matters near the sea. Keep calcium sulphate out of any room where the floor could stay wet: a wet room, a utility, or the boot room by the back door where wet boots come in after the beach. A cement based flowing screed does that job instead. If the sanded floor still needs to be brought to SR1 for thin vinyl, levelling the finished floor is the next step. For similar specifications along the coast, see anhydrite screed in Havant.
Anhydrite & Flow Screed prices in Selsey
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 Selsey
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 Selsey
As the crow flies, our yard in Slough is about 55.6 miles from Selsey, which lies to the south. Postcodes here include PO20, and Bognor Regis (6.4 miles), Chichester (7.2 miles), Emsworth (10.2 miles) and Havant (12.1 miles) are close by.
More on anhydrite screed, part of our screeding services.