Screeds
Sand and cement screed: cement bags and tonnes of sand
- where
- screed volume (m³)
- floor area (m²)
- screed thickness (mm)
- mass of dry materials including waste (kg)
- density of compacted screed, dry materials (kg/m³)
- waste allowance (%)
- cement (kg)
- sand parts per part cement, by weight
- sharp sand (kg; shown in tonnes)
- cement bag size (kg)
Explain this equation
Turns a floor area and screed depth into cement bags and tonnes of sharp sand for a traditional sand and cement screed. Use it when ordering materials.
V is the finished screed volume. ρ is how much the compacted dry materials weigh per cubic metre, about 2,000 kg. n is the mix ratio by weight, 4 for the standard 1:4 screed, so cement is one part in five and sand four parts in five. The waste allowance covers spillage and an uneven base.
Working by weight avoids the problem that loose sand bulks up and semi-dry screed compacts. The 1000 turns mm into metres. Bags are rounded up because you cannot buy part of a bag.
Sense check: 1 m³ of screed, about 20 m² at 50 mm, needs roughly 400 kg of cement (16 bags of 25 kg) and 1.6 tonnes of sand before waste.
Watch out: damp sand weighs more, so buy a little extra. Pre-bagged and ready-to-use screeds have their own yields.
Turns a floor area and screed depth into cement bags and tonnes of sharp sand for a traditional sand:cement screed.
Enter your values to see the result.
Good to know
BS 8204-1 gives nominal proportions of 1:4 cement to sand by weight, within limits of 1:3 to 1:4.5. Eurocode 1 lists cement mortar at 19–23 kN/m³ (about 1,900–2,300 kg/m³); 2,000 kg/m³ is used here as the mass of dry materials in a compacted semi-dry screed, because the mixing water adds a little to the hardened density. Bonded screeds are normally at least 25 mm (usually 40 mm), unbonded at least 50 mm, floating 65–75 mm. Use the depth at the deepest point if the base is out of level, or average several measurements.
Common mistake
Working from a volume ratio (shovels) and the wet volume. Semi-dry screed compacts a lot, so loose materials take up much more space than the finished screed.
Limits
Plain site-mixed screed only. Pre-bagged and ready-to-use screeds have their own yield figures. Sand moisture is ignored; damp sand weighs more, so allow extra if buying by the bag.
Sources
- Mineral Products Association Mortar Data Sheet 22: Screeds (BS 8204-1 nominal 1:4 cement:sand by weight, limits 1:3 to 1:4.5)
- BS 8204-1:2002+A1:2009 Screeds, bases and in situ floorings – Concrete bases and cement sand levelling screeds – Code of practice
- BS EN 1991-1-1 Eurocode 1, Annex A densities: cement mortar 19–23 kN/m³ (summary, Structville)
Results are calculations from the published methods and manufacturer figures shown, and depend on the data you enter. Always follow the tile, adhesive and grout manufacturers’ instructions, BS 5385 and the Tile Association guidance. Coverage rates vary by product and substrate. Check prices and VAT rules with your own records and HMRC.