Structural and base materials · Concrete & Cement
Cement Screed (Sand-Cement Floor Screed)
Describes the levelling and wearing layer laid by trowel over a structural deck, and separates it clearly from a poured levelling compound that only corrects an existing base.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What cement screed is
A cement screed is a layer of sand and cement, mixed relatively dry, spread over a structural floor and worked to level with a straightedge and float. Its job is to turn a rough or uneven structural deck into a flat, true plane that a floor finish can be laid on, and in some situations to act as the wearing surface itself.
The distinction from a self-levelling compound matters. A screed is laid to a thickness, compacted and levelled by hand, and it is that thickness that lets it bury pipes, form falls and take up substantial differences in the deck. A levelling compound is a flowable material poured as a thin correction layer over a base that is already broadly right; it finds its own level and cannot be built up the same way.
Screeds are described by how they sit on the floor. A bonded screed is laid directly onto a prepared structural surface it adheres to, an unbonded screed sits on a separating membrane, and a floating screed sits on insulation, which is the usual arrangement where underfloor heating pipes are embedded. Each behaves differently in shrinkage, curling and cracking, and the choice belongs to the designer.
Terminology
Common names and aliases
These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.
- Sand-cement screed
- Floor screed
- Traditional screed
- Semi-dry screed
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Levelling a structural concrete floor before tiles, resin, timber or resilient flooring are laid.
- Encasing underfloor heating pipes in a floating layer laid over insulation.
- Forming falls towards gullies in wet rooms, plant spaces and balconies.
- Making up levels between adjoining floor constructions so thresholds line through.
- Providing a base into which a thin final finish can be bedded.
- Raising a floor where services have to run within the depth of the build-up.
Consideration
Where it is commonly considered
- Where the structural deck is too uneven for a thin correction layer to resolve.
- Where pipes, cables or heating elements have to be contained within the floor build-up.
- Where a fall has to be formed across a floor rather than a flat plane.
- Where insulation is being placed under the floor surface and needs a layer above it.
- Where the floor finish supplier calls for a defined base to lay onto.
Professional review
Where additional professional review is especially important
These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.
- Where the structure has not been checked for the additional weight of a screed layer.
- Where drying before the floor finish goes down cannot be accommodated in the programme.
- Where the substrate is moving, deflecting or cracking and the cause has not been established.
- Where only a slight correction is needed and a levelling compound would be the discussion instead.
- Where a wet trade cannot reasonably be introduced into an occupied or already finished area.
Properties
Key properties to discuss
Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.
- Moisture behaviour
- A screed holds a large amount of water when laid and continues to release it for a considerable period afterwards. Floor finishes and adhesives depend on that drying having progressed far enough, and the measurement and decision belong to the flooring specialist.
- Installation dependency
- Screeding is a hand trade. The mix is spread between levels, compacted and closed with a float, and the flatness achieved depends on the operative, on the setting-out and on how the bay layout was planned before mixing started.
- Substrate dependency
- Whether the screed is bonded, unbonded or floating changes the preparation entirely. A bonded screed depends on the deck being clean, sound and correctly prepared, while a floating screed depends on the insulation beneath being stable and continuous.
- Thermal behaviour
- Where underfloor heating is embedded, the screed becomes part of the heating layer, and the way the system warms and cools is bound up with it. Commissioning and first heating follow the system supplier's own documentation.
- Surface wear
- A screed left as the visible surface behaves differently from one used as a base beneath a finish. Where it is walked on directly, dusting, marking and abrasion become points to discuss with the specialist laying it.
- Repairability
- Local areas can be cut out and replaced, but a patch in a screed rarely matches in level, colour or texture, and hollow or debonded areas frequently extend further than they first appear when tapped.
- Documentation
- The screed specification, the mix used, the bay layout and the record of drying assessments are what a flooring installer will ask for before laying anything over it.
Exposure
Exposure and environmental conditions
- Will the floor sit in a wet area where water can reach the screed regularly?
- What temperature and ventilation conditions will the screed be drying under?
- Is the building weathertight before the screed is laid, and will it stay that way?
- Will underfloor heating be present, and how does the commissioning sequence affect drying?
- Is any part of the floor exposed externally or open to a semi-heated space?
Assembly
Substrate and system dependencies
What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.
- The structural deck has to be able to carry the weight of the screed and everything above it.
- Bonded work depends on preparation of the deck, and the method used affects whether adhesion is achieved.
- Insulation under a floating screed has to be laid without gaps or boards that rock underfoot.
- Separating and damp-proof layers have to be continuous and lapped where the design calls for them.
- Perimeter edge strips and movement joints are installed before the screed is placed.
- Underfloor heating pipes are fixed and pressure-tested in line with the system supplier's information.
Appearance
Appearance and finish considerations
- A screed is usually a base rather than a finish, so its appearance matters mainly through the finish above it.
- Trowel marks, bay joints and colour variation show up if the screed is left exposed.
- Surface flatness tolerance affects thin, rigid finishes far more than thick or resilient ones.
- Curling at edges and joints can lift a thin finish laid over it if it is not addressed first.
- Where the screed is to be sealed and used as the visible floor, the finishing technique is agreed in advance.
Durability
Durability questions
Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.
- Has the screed type been chosen with the intended floor finish in mind?
- What is the plan for movement joints, and do they continue through the finish above?
- How will the screed be protected from traffic and loading while it hardens?
- How will hollowness or debonding be checked before the floor finish is laid?
- What curing arrangements are in place, and who is responsible for them?
Upkeep
Maintenance and repair considerations
- If a hollow area is found later, how would it be repaired without disturbing the finish?
- Would a repair need the same mix, and is the original specification recorded anywhere?
- How are cracks in a screed assessed, and when do they matter to the finish above?
- If underfloor heating pipes are embedded, how would a leak be located and reached?
- What should be checked before laying a new floor covering over an existing screed?
Installation
Installation dependencies
What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.
- Access for materials and mixing has to be arranged, and screeding is disruptive while it happens.
- Bay layout, day joints and finished levels are set out before mixing starts.
- Following trades have to stay off the floor for the period the specialist sets.
- Drying conditions have to be managed, and forcing drying too quickly can cause its own problems.
- The flooring installer's requirements are better known before the screed is specified than after.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- The screed specification, including whether it is bonded, unbonded or floating.
- The mix or proprietary product information supplied by the screeding specialist.
- Records of moisture assessments carried out before the floor finish was laid.
- The underfloor heating supplier's requirements where pipes are embedded in the layer.
- The floor finish manufacturer's requirements for the base it is laid on.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Is this screed bonded, unbonded or floating, and why that arrangement here?
- Can the existing structure take the weight of the proposed build-up?
- What does the floor finish supplier require of the base beneath it?
- How will we know when the screed is dry enough for the finish to go down?
- Where are the movement joints, and do they need to continue through the tiles or boards?
- How flat does this floor need to be for the finish we have chosen?
- If underfloor heating is included, what is the commissioning sequence?
- Would a levelling compound do what is needed here instead of a screed?
Blind spots
Commonly overlooked points
- Screed drying often controls the programme more than any other floor operation on a project.
- Raising the floor level affects doors, thresholds, stair risers and skirting heights.
- A screed can be flat and still not suit the finish above if that finish needs a different tolerance.
- Movement joints that stop at the screed and are tiled over usually reappear as cracks in the tiling.
- The weight of a screed over a timber floor is a structural question rather than a finishing one.
What this page does not do
- Whether a floor can carry a screed is a structural matter for a qualified professional.
- This entry does not state that any screed suits wet areas or forms part of a water-managing assembly, which depends on the whole design.
- Drying assessment before a floor finish is laid is a specialist judgement that this page cannot set.
- Build Design Hub does not supply, test, approve or endorse screed materials or those who install them.
Related entries
Related materials
Materials from the same family, an adjacent role in the assembly, or a shared application.
Inspiration
Related Ideas Library pages
Design directions where this material commonly appears.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this material comes up.
Go deeper
Related Build Design Hub guides
Planning guidance and neutral comparisons behind the decisions on this page.
Concrete & Cement Materials
Reference entries for cement-based materials — ready-mixed and precast concrete, screeds, levelling compounds, renders of the cementitious family and the admixtures that modify them.
Browse all concrete & cement entries →