Calcium sulphate grades for Southampton apartment floors
Architects' drawings name this screed by a short grade code, and its letters and numbers follow the European standard written for screed materials. The CA at the front means calcium sulphate. The C and F numbers that follow are compressive and flexural strength, both in N/mm2. For a lightly used floor in a house, the grade is CA-C20-F4. CA-C25-F5 suits most homes, apartments and offices, which covers most apartment floors in a city where so many homes are flats. Floors that will work harder get CA-C30-F6.
For a Southampton apartment block or a new plot, the grade comes from the engineer, and that grade is what goes in. Occasionally a Southampton spec names an alpha hemihydrate mix rather than one of these grades, picked when a quicker drying or thinner floor is needed. Its maker's data sheet says how deep to lay it, how long it dries and how the heating comes up, and our pour follows that sheet in any Southampton block.
It hardly shrinks while it sets. So big bays can go down with few joints, a good fit for open-plan apartments and long corridors. Doorways and the line between two heating zones still take a joint, and we mark out the bays and joints in advance of the pour.
Our own team builds the layers underneath first (insulation, membrane and edge strip), so nothing is poured onto an unchecked base. Our anhydrite explainer goes deeper into the material.
Sanding and testing before Southampton floors are laid
Looking dry does not make a calcium sulphate floor ready for flooring. As the water leaves it, a fragile skin called laitance forms across the top. Unless that layer is sanded away before adhesive, primer or compound goes on, the finish grips the weak skin and can lift later. Sanding is followed by priming, and the primer has to be one that calcium sulphate will take.
Moisture is the next hurdle. Calcium sulphate often has to be drier than cement before flooring goes down, as many manufacturers set a lower limit for it, so we check it with a hygrometer before handover. If the flat has underfloor heating, running it from about 7 days will usually force dry the screed, following the warm-up on our Southampton heated floor screed page.
One thing never changes: calcium sulphate is kept out of any room where the floor might get wet. Any wet room, walk-in shower or floor that might suffer a leak is poured with a cement based flowing screed instead. If the slab beneath a Southampton flat is not ready to pour onto, preparing the floor first is a separate job we also take on. The same anhydrite service is offered in Fareham.
Anhydrite & Flow Screed prices in Southampton
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 Southampton
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 Southampton
Southampton is about 54.4 miles south-west of our Slough base as the crow flies, with postcodes including SO14, SO16, SO15 and SO17. The nearest towns to it are Totton (3.8 miles), Hedge End (4.4 miles), Eastleigh (5 miles) and Romsey (7.2 miles).
More on anhydrite screed, part of our screeding services.
