Anhydrite grades for new Watford apartment floors
Specifications describe calcium sulphate screed with a short code from the European screed standard. CA says what it is, then C gives compressive strength and F flexural strength, each in N/mm2.
Most buildings use one of three grades. Light domestic traffic calls for CA-C20-F4. Step up to CA-C25-F5 for the majority of homes, apartments and offices. Anything busier moves up to CA-C30-F6. The right one depends on the loads the floor will carry, not on the depth of the pour.
On a scheme such as Watford Riverwell, or any new build plot, the grade is the engineer's call and our pour follows it. A tight timetable or a shallow build-up sometimes leads the designer to an alpha hemihydrate material. For those, depth and drying are taken from the product's own sheet.
One reason developers choose calcium sulphate is its low shrinkage. That lets an open-plan flat be laid in broad bays, with only a few joints. We mark out the ones it does need, across door thresholds and between heating zones, before pouring starts.
Wet areas are where it falls down. Where a floor may get wet, such as wet rooms, shower areas or parts of a building left open during construction, a cement based flowing screed is used instead, and we can supply that. There is more about how it behaves in our anhydrite material guide.
Laitance, primers and moisture limits in Watford flats
As it dries, the top of a calcium sulphate floor turns into laitance, a thin and weak crust. Stick a floor finish straight onto that and it can come away with the crust, so sanding comes before any adhesive. Priming follows, using a primer formulated for calcium sulphate, since a cement primer may not hold.
Moisture testing follows. Flooring makers tend to demand a drier reading from calcium sulphate than from cement, and a reading that clears sand and cement can still leave this screed too damp for the adhesive. The test is done with a hygrometer; the date on the calendar proves nothing. If the flat has pipes in the floor, force drying usually begins at about 7 days. The flooring fitter gets a written account from us covering drying, the laitance work and the reading the floor gave, so they know exactly where things stand.
If the flooring needs a flatter surface than the screed gives, for example thin sheet vinyl, a thin levelling coat goes on after priming. For projects nearby, see our anhydrite screed in Hemel Hempstead page.
Anhydrite & Flow Screed prices in Watford
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 Watford
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 Watford
Watford is about 13.7 miles north-east of our Slough base as the crow flies, with postcodes including WD17, WD19, WD25 and WD18. The nearest towns to it are Bushey (1.5 miles), Rickmansworth (3.4 miles), Harrow (5 miles) and Chorleywood (5.4 miles).
More on anhydrite screed, part of our screeding services.
