Advanced options
Traditional sand/cement screed at about 2,000 kg/m3, semi-dry mix. Typical depths: 65mm bonded over concrete, 75mm+ floating over insulation, 65-75mm covering underfloor heating pipes. Liquid anhydrite screeds pour thinner and are quoted by the m2 instead.
What The Screed Calculator Works Out
- Screed volume: floor area multiplied by depth, with the weight at about 2,000 kg per m3. 20 m2 at 65mm is 1.3 m3 and 2.6 tonnes of material, which arrives as a small mountain and mixes in relays; a forced-action mixer hired for the day beats a drum mixer, which never mixes semi-dry screed properly.
- Sharp sand: the mass split by the mix ratio. At 4:1 the sand is four fifths of the total, roughly 2.1 tonnes for that 20 m2 floor. 3:1 is stronger for thin bonded screeds and heavy use; 5:1 is an economy mix for thick floating screeds.
- Cement: the remaining fifth (at 4:1) in 25 kg bags, about 21 bags for the example. The mix is semi-dry, just wet enough to ball in the hand without dripping, compacted hard and ruled flat between battens.
- Typical depths: 25 to 40mm fully bonded to prepared concrete with a slurry grip coat, 50mm minimum on a separating membrane, 65mm minimum floating over insulation (75mm commercial), and 65 to 75mm total to cover underfloor heating pipes.
- Wastage and density (advanced): add 5% to 10% for uneven bases and spillage, and change the density if your supplier quotes a different figure (fibre-reinforced or lightweight screeds vary).
- Sand bulk bags (advanced): sharp sand is sold in bulk bags of about 800 to 900 kg; the calculator rounds up to whole bags and shows the spare. Loose tipped loads are cheaper per tonne for anything over three bags.
- Site-mixed cost (advanced): bulk bags and cement bags at your prices. Typical UK prices are GBP 55 to GBP 80 per bulk bag of sharp sand and GBP 6 to GBP 9 per 25 kg of cement, so materials for a 20 m2 floor at 65mm come to roughly GBP 300 before mixer hire.
- Ready-mixed screed cost (advanced): the volume at a delivered price per m3. Retarded ready-mixed screed typically costs GBP 120 to GBP 200 per m3 and removes both the mixing labour and the consistency gamble; liquid anhydrite screeds are quoted per m2 instead.
- Drying time (advanced): the industry rule of one day per millimetre up to 40mm and two days per millimetre beyond, before moisture-sensitive finishes such as wood or vinyl. A 65mm screed is a 90-day wait without forced drying, though you can walk on it after a week. The depth table shows volumes, materials and drying times for common depths.