Calcium sulphate grades for Swanley flats and plots
Anhydrite screeds carry a label like CA-C25-F5. Here CA means calcium sulphate, 25 is the compressive strength and 5 the flexural strength, both in N/mm2, following the European standard for screeds.
Three grades cover nearly all housing. A lightly used house floor can take CA-C20-F4. Specifications for flats, offices and the majority of homes tend to ask for CA-C25-F5. Where a floor will be worked hard, the specification moves up to CA-C30-F6. On new blocks and plots, the grade is the engineer's call, and we pump what was chosen, with no swaps.
A drawing might instead specify an alpha hemihydrate product rather than a CA grade. Designers pick these when the floor must dry sooner or be shallower, and the maker's data sheet then governs depth, drying and heating, so that sheet is what we pour to.
The reason developers like calcium sulphate for apartments is its low shrinkage. Wide bays go down with hardly any joints, ideal for an open-plan flat or a long communal corridor. Any joints that are needed, typically at doorways or on the line between two heating zones, are drawn up before pumping begins.
Homes built since 2015 are 8% of Swanley's stock, and new plots and blocks are where a written specification usually comes with the enquiry. To understand the material better, try what anhydrite screed is.
Sanding, priming and testing anhydrite in Swanley
Calcium sulphate leaves a soft skin, laitance, on its surface as it dries out. Glue and compound will not hold onto that skin, so we sand it away when the floor has dried sufficiently. Priming follows, with a product made to work on calcium sulphate, as some cement primers are not suitable.
Moisture comes next. The weeks since pouring prove nothing, because flooring makers often give calcium sulphate a tighter moisture limit than cement screed; a hygrometer reading settles it. If the floor has heating pipes, running them gently from around day 7, on a stepped schedule, normally speeds the drying.
There is one place anhydrite should never go. Prolonged water softens it, so a Swanley wet room, a level-access shower or a utility room that could flood should get a cement based flowing screed or hand-laid sand and cement.
Where a finished anhydrite floor needs a smoother surface for sheet vinyl, it can be levelled after sanding and priming; see levelling compound for Swanley floors. The same specification work is also offered in Bromley.
Anhydrite & Flow Screed prices in Swanley
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 Swanley
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 Swanley
As the crow flies, our yard in Slough is about 36.5 miles from Swanley, which lies to the east-south-east. Postcodes here include BR8, and Bexley (4.4 miles), Dartford (5.2 miles), Bromley (5.5 miles) and Swanscombe (6.2 miles) are close by.
More on anhydrite screed, part of our screeding services.
