Screed vs Concrete: What's the Difference?

What concrete is

Concrete is cement, sand, water and coarse stones. It's strong, and it's used for slabs, foundations and structural floors. The surface is usually too rough and uneven to lay a finished floor straight onto.

What screed is

Screed is a finer mix: cement and sharp sand with no big stones, or a liquid screed. It's laid on top of the slab or the insulation to give a flat, level surface ready for tiles, timber, vinyl or carpet, and it's usually where the underfloor heating pipes go.

Why a slab still needs screed

• Slabs are rarely flat or level enough for a finished floor
• Underfloor heating pipes need to be covered, and screed does that
• Insulation goes on the slab, and the screed goes on the insulation
• Screed gives the tiler or floorer a true, smooth base

Typical floor build-up in a new Irish house

• Hardcore, compacted
• Sand blinding
• Damp-proof membrane and radon barrier, required on new homes in Ireland
• Concrete slab
• Insulation
• Underfloor heating pipes, if you're having them
• Screed
• Floor covering

The order can change with the design, so go by your engineer's or architect's drawings.

The mix is different

Concrete has coarse stones in it for strength. Screed is usually around one part cement to three to five parts sharp sand, with no big stones, which is what lets it be finished smooth and level. Liquid screeds are a different mix again, made to flow.

Polished concrete is a different job

Polished concrete floors are concrete slabs ground and polished as the finished floor. That's a specialist finish of its own. A screed is normally covered by tiles, timber, vinyl or carpet.

When you need both

Most new builds and extensions have both: a concrete slab, then insulation and underfloor heating, then screed. We pour slabs and foundations as well as screed, so one crew can do the lot.

From JAM Floor Screeding, Portlaoise. Over 20 years laying screed across Leinster. Figures here are typical guidance; your floor's spec and the manufacturer's data sheet always come first.