Screed Types: Bonded, Unbonded and Floating Explained

A screed is the thin, level layer of sand-and-cement mix laid over a structural slab to receive the final floor — tiles, laminate, vinyl. It isn't structural concrete; it's a finishing layer, and it comes in three types that behave very differently. We supply screed mixes for all three.

Bonded Screed

Laid directly onto a roughened, primed slab so the two act as one. Thinnest of the three — typically 20–50 mm — and the right choice where finished floor levels are tight and the slab beneath is sound. Bond is everything: a poorly prepared substrate means the screed delaminates and drums under foot traffic.

Unbonded Screed

Deliberately separated from the slab by a damp-proof membrane. Because it moves independently, it needs more thickness — typically 50 mm and up for a standard sand-cement screed. Used over damp slabs or where a DPM is part of the build-up.

Floating Screed

Sits on an insulation layer — the standard build-up for underfloor heating, where the screed encapsulates the pipes. Typical thickness is 40–75 mm depending on the system and pipe diameter. The insulation makes the screed the thermal mass that stores and radiates heat, so compaction and coverage over the pipes directly affect heating performance.

Choosing and Ordering

The type is decided by the floor build-up, not by preference — your drawing or flooring contractor specifies it. What we control is the mix: consistent, workable, and fine enough to close over pipes. Volume is easy to get right: screed is thin, so measure carefully (a 40 mm screed over 50 m² is just 2 m³ — see our concrete calculator). For more answers, the FAQ covers screed thickness for underfloor heating, and our sales team can advise on mix selection.

Technical review pending — this article is awaiting sign-off by Quick-Mix technical staff before deployment.

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