Grades and bays for Portsmouth apartment floors
A specification line such as CA-C25-F5 tells you three things. CA marks the material as calcium sulphate. The 25 after C is how hard it resists crushing and the 5 after F how well it resists bending, each given in N/mm2 under the European screed standard used in Britain.
Each common grade has its job. Lightly used house floors can be CA-C20-F4; the general run of homes, apartments and offices sits at CA-C25-F5; and floors that take harder wear go up to CA-C30-F6. A block of flats usually sits in the middle grade, while communal areas and commercial ground floors may call for the higher one.
If a scheme needs a floor that dries sooner or sits thinner, the designer may pick an alpha hemihydrate product instead, and its own data sheet then sets the depth and heating, which we follow on site.
The big advantage in a block is low shrinkage. Bays can be much larger than cement allows, so an apartment floor can go down with few joints. Joints are not left to chance, though: we draw out bays first, with door thresholds and the boundaries between heating zones getting the closest look.
Big schemes on the horizon make this more relevant. The planned Lennox Point at Tipner West is set to bring more than 3,500 homes, the sort of development where the specification names a grade. For how the material behaves in practice, see our anhydrite screed guide. The pumping side is covered on our liquid screed page.
Sanding and testing anhydrite in Portsmouth flats
Calcium sulphate is not ready for flooring when it is dry to the touch.
First, the surface laitance has to go. It is a fragile skin that rises to the top while the screed cures. We sand it away when the screed has dried; leave it on and the adhesive bonds to that crust instead of solid screed, and the new floor can come loose. Our floor preparation team handles sanding and cleaning.
Moisture testing comes next. Flooring makers often allow less moisture in calcium sulphate than in cement, so read the data for the product going down instead of trusting a rule of thumb. In a heated flat, the system can usually help dry the floor from around day seven.
Once it passes, the surface is primed with something made for calcium sulphate. Check that the primer and adhesive are both approved for calcium sulphate, as the bond depends on it.
Finally, keep it away from water. Anhydrite is not suitable where a floor may get wet, such as communal bin stores, wet rooms or ground floors at risk of damp. Those spots take a cement based flowing screed, which still goes in by pump.
Anhydrite & Flow Screed prices in Portsmouth
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 Portsmouth
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 Portsmouth
Portsmouth is about 54.4 miles south-south-west of our Slough base as the crow flies, with postcodes including PO1, PO3, PO2 and PO6. The nearest towns to it are Gosport (1.4 miles), Fareham (5.3 miles), Havant (6.2 miles) and Emsworth (7.6 miles).
More on anhydrite screed, part of our screeding services.