Short answer: concrete contains coarse aggregate (gravel) and forms the strong, structural slab of a floor. Screed is a finer mix of sand and cement, or a flowing liquid, laid on top of the slab or insulation to create a smooth, level surface ready for the floor finish. Most floors use both: concrete for strength, screed for flatness.
Concrete
- Cement, sand, coarse aggregate and water
- Structural: carries loads, typically 100 mm thick or more in ground-bearing slabs
- Rough, uneven surface not intended as a finished floor in homes
Screed
- Cement and sharp sand, or a calcium sulphate or cement-based liquid
- Not structural: spreads loads and creates a level surface
- Usually 25 to 75 mm, depending on type and build-up
- Smooth finish, ready for tiles, LVT, wood or carpet once dry
Can you use concrete instead of screed?
For a finished floor in a home, not usually. Concrete is hard to finish to the flatness modern floor coverings need, and laying it over insulation or underfloor heating at screed depths is not appropriate. In some industrial settings a power-floated concrete slab is used as the finished floor.
See our concrete flooring and floor screeding services.
Written by Ben Phillips, director of Chelmsford Floor Screeding Ltd, floor screeding contractors based in Billericay with 20+ years of experience across Essex and London. More about us.