Reading an anhydrite specification for a Bicester plot
Anhydrite grades are written as a short code drawn from the European standard that governs screed. CA at the front stands for calcium sulphate. After it, C gives compressive strength and F flexural strength, each measured in N/mm2. Housing specifications nearly always use one of three.
For a lightly used domestic floor you will see CA-C20-F4. Most houses, flats and offices are specified at CA-C25-F5. Heavier wear moves the floor up to CA-C30-F6. Whichever appears on a Bicester engineer's note goes into the floor unchanged, with no cheaper substitute.
Now and then a drawing calls for an alpha hemihydrate screed in place of a standard grade. Designers pick these when the floor must dry quicker or be laid thinner, such as over heating pipes where every millimetre of height counts. Each comes with its own data sheet covering depth, drying times and first heating, and that sheet, not a rule of thumb, governs how we lay it.
Because calcium sulphate barely shrinks while it cures, big open bays can be poured with hardly any joints. Purpose-built flats are 9% of Bicester's homes, and a whole apartment floor can usually be poured in a single visit. Any joints that are needed, say at a doorway or where one heating zone meets another, are marked out on the plan ahead of pouring.
One firm limit applies. Calcium sulphate does not tolerate water, so wet rooms and areas that may flood need a cement based flowing screed or a traditional screed instead. For more on the chemistry, read anhydrite screed explained.
Laitance, moisture tests and primers in Bicester homes
Anhydrite needs finishing work after it dries, and skipping it can make the flooring fail.
A soft film called laitance builds up on the surface while the screed settles. Adhesive or compound stuck to that film can let go, taking the flooring with it, so the film has to come off first. Once the floor is dry enough, the surface is sanded to take the skin off and expose sound screed, then vacuumed. Our floor preparation service covers sanding and cleaning where a builder wants it done separately.
Moisture testing comes next. Flooring makers often allow less moisture in calcium sulphate than in a cement screed, so the number to aim for is whatever your chosen product's maker states. A hygrometer test measures relative humidity at the surface and gives a reading you can hand to the fitter. Where pipes run through the screed, switching the heating on from around 7 days usually speeds the drying.
Last comes a primer made to work on calcium sulphate. The primer has to be matched to the screed, so tell us which adhesive or compound will follow. If the surface then needs a smoother finish, see levelling over anhydrite.
When we leave, you get written notes on drying and laitance to pass to the flooring fitter.
Anhydrite & Flow Screed prices in Bicester
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 Bicester
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 Bicester
As the crow flies, our yard in Slough is about 33.3 miles from Bicester, which lies to the north-west. Postcodes here include OX26, and Kidlington (7.8 miles), Brackley (9.4 miles), Buckingham (10.1 miles) and Oxford (11 miles) are close by.
More on anhydrite screed, part of our screeding services.
