Reading a calcium sulphate grade for Tonbridge
On a drawing, anhydrite shows up as a code from the European screed standard used in Britain. Take CA-C25-F5: the CA tells you the binder is calcium sulphate, the figure after C is how much it resists crushing and the figure after F is how much it resists bending, each given in N/mm2.
Three grades cover most work. A house floor with little foot traffic can take CA-C20-F4. The middle grade, CA-C25-F5, covers the bulk of houses, flats and offices. CA-C30-F6 is chosen for heavier use. If your drawings name one, we match it; if they do not, the use of the room decides.
Then there are alpha hemihydrate screeds, which sit outside that grading. Specifiers pick them when the floor has to dry sooner or be laid thinner, and the maker's own data sheet sets the depth and drying for each one, not the usual rules of thumb.
Calcium sulphate barely shrinks, so big bays can go down with only a handful of joints compared with cement. Across a block of flats or a run of new plots, where every floor is one wide open area, that saves a lot of cutting. Bays and joints are still marked out in advance, with doorways and changes of floor shape getting the closest attention.
Tonbridge is not dominated by new build, with 11% of its homes dating from 2000 to 2014. On an extension or one-off plot where nobody has written a grade down, we propose one based on what each room will be used for. For the chemistry behind the material, read anhydrite screed in more detail.
Laitance, moisture tests and primers in Tonbridge
While it cures, calcium sulphate throws up a soft, thin crust known as laitance. When drying is complete, that crust must be sanded away; leave it and the glue holds onto the crust instead of the screed, and the tiles or vinyl can come loose months down the line.
Moisture testing is the next step, and it is stricter than for cement. Plenty of flooring makers allow less moisture in a calcium sulphate base than in a cement one, so a figure that is fine for sand and cement can be too wet here. Running the heating from around day 7 to force dry the floor usually gets it to that figure faster.
With the sanding done and the reading passed, the floor gets a primer made to work on calcium sulphate. A primer meant only for cement screeds is the wrong choice here, so the primer matters as much as the adhesive. For very thin finishes, a skim of self levelling compound can follow the primer.
Keep anhydrite out of rooms where water may sit. A ground floor shower room, wet room or utility in a Tonbridge house is better served by a flowing screed with a cement binder, or by a hand-laid traditional floor.
Anhydrite & Flow Screed prices in Tonbridge
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 Tonbridge
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 Tonbridge
As the crow flies, our yard in Slough is about 46.1 miles from Tonbridge, which lies to the east-south-east. Postcodes here include TN9 and TN10, and Royal Tunbridge Wells (4.1 miles), Sevenoaks (6.4 miles), Crowborough (10.3 miles) and Snodland (12 miles) are close by.
More on anhydrite screed, part of our screeding services.