Sand cement screed: thickness per type, drying time, mix ratio, cost and crack control with shrinkage fibre

A sand cement screed is a semi-dry mix of cement and sharp sand (usually 1:3 to 1:4.5) laid over a slab or insulation as a level base for the floor finish. Typical thickness: bonded 25–40 mm, unbonded 50 mm or more, floating 65–75 mm. Drying time: about 1 day per mm up to 40 mm, then 2 days per mm.

Shrinkage fibre mixed into the screed limits cracking while it dries. Below you will find a thickness table per screed type, the maximum thickness, drying time per thickness, the mix and screeding sand, laying, cost and crack control.

What is a sand cement screed?

A sand cement screed, also called a cement screed or, in the UK, a traditional screed (as opposed to a liquid or flowing screed), is a semi-dry mix of sand, cement and water applied on top of a load-bearing floor; in Belgium it is known as a chape. The screed smooths out irregularities, bridges level differences and conceals underfloor heating or electrical pipework. It is the most common screed in Dutch and Belgian housing, in both new build and renovation.

A sand cement screed is not structural and contains no coarse aggregate, so it is not concrete: its job is to provide a flat, level surface for the finish. The load-bearing slab underneath is designed separately; see concrete floor slab thickness.

Do not confuse the screed with a monolithically finished concrete floor: with a power-floated concrete floor, the structural floor itself is the final finish, whereas a screed is always a separate layer on top of the structural floor. Depending on how they are laid, screeds fall into three types:

• Bonded screed: applied directly to the roughened and primed structural floor; slab and screed act together.

• Unbonded screed: laid on a separating membrane; the screed moves independently of the substrate.

• Floating screed: laid on an insulation layer (thermal or acoustic), with no contact anywhere with the structural floor or walls.

This article belongs to the pillar applications and target groups, where you will also find the adjacent flooring topics.

Sand cement screed or liquid screed?

In the UK the main alternative to a traditional sand cement screed is a flowing (liquid) screed. The two differ mainly in how they are laid and how thin they can be:

• Sand cement screed: semi-dry, spread and compacted by hand or placed by pump, with the thicker minimums in the table below. It suits most floor finishes and takes fibres straight in the mixer.

• Flowing screed: cement-based or calcium sulphate-based, pumped and self-levelling, and thinner than a sand cement screed. For calcium sulphate flowing screeds BS 8204-7 gives unbonded 30 mm, floating 35 mm (domestic) and 45 mm over underfloor heating with 25 mm cover; for cement-based flowing screeds, follow the manufacturer. It can be walked on after 24–48 hours.

Calcium sulphate screeds have their own drying and priming rules, so follow the manufacturer's instructions. Flowing screeds on insulation are covered in the article on the floating screed.

Sand cement screed thickness: how thick should a screed be?

The right cement screed thickness depends on how the screed is laid (bonded, unbonded or floating) and on the load. The table gives the UK minimums from BS 8204-1, with Dutch practice where it differs; for heavier floor loads the structural engineer or screed contractor specifies a thicker layer.

The 65 mm limit for floating screeds is not arbitrary: a thinner floating screed lacks the stiffness to accommodate deformation of the insulation layer. For floating screeds thinner than 65 mm, crack-control mesh combined with fibre reinforcement is therefore recommended (Dutch practice; in the UK, going below the BS 8204-1 minimum needs the designer's approval); the mesh then also helps to cope with any compression of the insulation. If the screed lies on a firm, barely compressible insulation layer, fibre reinforcement alone can suffice, because no deformation occurs and the reinforcement only needs to control the shrinkage.

Exactly how a floating screed is built up (edge strips, choice of insulation, acoustic requirements) is covered in the separate article. The combination with heating pipes demands extra attention to thermal movement; see underfloor heating and fibre concrete.

Also check the weight: a sand cement screed weighs roughly 20 kg per m² for every 10 mm of thickness, so about 100 kg per m² at 50 mm (indicative). On timber or older suspended floors, have the load-bearing capacity checked before you settle on a thickness.

Maximum screed thickness: how thick can a sand and cement screed be?

Standards set minimum thicknesses rather than one fixed maximum. In UK practice a bonded screed is kept to about 40 mm (Dutch practice sometimes goes to 50 mm), because thicker bonded layers are more likely to de-bond and are usually laid unbonded instead. Traditional screeds much beyond roughly 75–100 mm are rare, because drying time, weight and curling risk all rise with thickness (indicative).

• Drying time: by the UK rule of thumb, a 100 mm screed needs around 160 days before floor coverings can go down.

• Weight: about 200 kg per m² at 100 mm, which matters on suspended floors.

• Alternatives for a deep build-up: take up the extra height with insulation or a lightweight fill under a normal 65–75 mm floating screed, or have a (fibre-reinforced) concrete topping designed; see how thick a concrete floor should be.

Sand and cement screed mix ratio

The classic cement screed ratio lies between 1:3 and 1:4.5 (cement : sharp sand), the range UK guidance gives. A 1:4 mix is the everyday sand and cement screed mix; 1:3 gives a stronger screed and is used for thin bonded layers or more heavily loaded floors. The most important quality factor is not the cement content but the water: a sand cement screed is laid semi-dry, with just enough water to form a mouldable ball that does not slump. The ball test shows whether the mix is right: a squeezed handful holds its shape without water running out.

The more mixing water, the greater the drying shrinkage and therefore the cracking risk. A plasticiser (an admixture that improves workability without extra water) reduces the water demand and with it the shrinkage. Fibres are added in the same mixing step: on screed projects, the screed contractor doses around 1 kg of shrinkage fibre per m³ of mortar, straight into the mixer or the pump's forced-action mixer.

Screeding sand: which sand to use

For screeding, use clean, washed sharp sand, also sold as grit sand or screeding sand (in Belgium Rhine sand is common), with a grading of roughly 0/4 mm. The angular grains lock together when compacted and give a firm, stable layer.

Do not use soft building sand. It is fine and rounded, made for bricklaying mortar, needs more water, shrinks more and leaves a weaker surface. Pre-bagged screed mortar or factory-mixed screed from a plant avoids batching errors on site, which is worth considering when the mix has to be consistent across a large floor.

How much sand and cement per m²?

Mixed sand cement screed has a density of roughly 2,000 kg/m³, so you need about 20 kg of mixed screed per m² for every 10 mm of thickness (indicative). Worked examples:

• 50 mm thick: about 100 kg per m², or about 4 bags of 25 kg of pre-mixed screed per m². Batched on site at 1:4 by weight, that is about 20 kg of cement and 80 kg of sharp sand per m².

• 20 m² at 65 mm: 20 × 0.065 = 1.3 m³ of screed, about 2.6 tonnes of material.

• Fibre: at around 1 kg per m³, the 1.3 m³ in this example needs about 1.3 kg of shrinkage fibre.

On top of these quantities, allow 5–10% for waste as a practical margin. For the fibre, multiply area × thickness × about 1 kg/m³: at 65 mm that is about 65 g per m², so a 10 kg box covers roughly 150 m² of screed (indicative).

Laying a cement screed: how the pour proceeds

Laying the screed (in practice more spreading than pouring, because the mix is semi-dry) follows fixed steps:

• Preparation: structural floor clean and dust-free; for a bonded screed a cement slurry bonding coat (primer), for an unbonded screed a membrane, for a floating screed insulation plus edge strips along all walls and upstands.

• Setting out levels: with a laser and level markers or narrow screed rails of mortar, so the floor comes up to level everywhere. The required flatness depends on the finish: in the UK, BS 8204 sets surface regularity classes SR1 to SR3 (SR1 = max. 3 mm under a 2 m straightedge); in the Netherlands NEN 2747 applies.

• Mixing and transport: on small jobs with a screed mixer, on larger ones with a pump that carries the mortar tens of metres and several storeys up.

• Spreading and levelling: the mortar is distributed between the rails, compacted and ruled off with a long straightedge.

• Closing the surface: the surface is finished with a float for an even, flat skin.

• Curing: cover the floor or keep it moist for the first few days, and avoid draughts and forced drying. If the surface dries much faster than the underside, the screed curls up at edges and joints.

A traditional screed crew typically lays in the order of 100–150 m² a day (UK cost guides mention around 125 m²), depending on access and pumping (indicative). Laying it yourself is feasible for small areas, but flatness and the correct water content are demanding, and mistakes can only be corrected afterwards with levelling compound or grinding.

Sand and cement drying time: how long does a screed take to dry?

Sand and cement drying time depends on thickness: the UK rule of thumb is about 1 day per mm up to 40 mm and 2 days per mm beyond that, so a 50 mm screed needs about 60 days before moisture-sensitive flooring. The table sets it beside the Dutch rule of thumb (1 week per centimetre up to 4 cm, then 2 weeks per centimetre), which gives shorter times.

Both rules are rough guides: ventilation, temperature and the chosen finish change the result, so measure before you lay the flooring. Setting, taking load and drying are three different stages:

• Set: light foot traffic after 24–48 hours.

• Load: light loads such as partition walls and storage after about a week; full strength after about 28 days.

• Dry: ready for moisture-sensitive flooring only when a moisture test says so.

That long drying time is about residual moisture, not strength. Tiles in a cement-based adhesive can sometimes go down earlier, if the adhesive manufacturer's data sheet allows it; vapour-tight finishes such as vinyl, resin floors and parquet need a dry screed. Dutch practice measures this with the carbide (CM) method: vapour-tight finishes usually require no more than about 2.0% CM, often 1.8% with underfloor heating. UK practice uses a hygrometer reading in % relative humidity per BS 8203, typically 75% RH for resilient floor coverings. Whatever the method, always follow the flooring supplier's instructions.

With underfloor heating a heat-up protocol also applies. UK guidance usually allows around 21 days before the heating is gradually started; the floor is then warmed up and cooled down in steps before the finish goes down, so thermal stress is released in a controlled way. The details are in underfloor heating and fibre concrete.

Drying can be sped up only to a degree: ventilate without draughts, run dehumidifiers after the first week, or choose a fast-drying screed mortar, for which manufacturers state their own drying times. What does not work is heating hard in the first days: the surface then dries faster than the core can release moisture, resulting in curling and cracks.

What does a sand cement screed cost per m²?

Indicative prices for having a sand cement screed laid in the Netherlands, including material and labour (2026 price level, depending on region, area and access). Prices in the UK and other markets differ, so treat these as a Dutch reference, and check whether a quotation includes VAT:

• Bonded screed 30–40 mm: €20 to €27 per m²

• Unbonded screed 50 mm: €25 to €30 per m²

• Floating screed 65–70 mm: €30 to €40 per m² (excluding insulation and edge strips)

• Screed with underfloor heating 70–80 mm: €30 to €42 per m² (excluding the heating system)

• Small areas (under 40 m²): expect a higher price per m² because of fixed delivery and start-up costs

• Fibres in the mix: roughly €2 to €5 per m² extra in quotations

The choice of reinforcement mainly affects the labour: crack-control mesh has to be laid out, overlapped and set on chairs, whereas screed fibres instead of crack-control mesh go straight into the mixer, which saves laying time. If you want to know the fibre quantity for your project, request a quotation with your area and floor build-up.

Preventing cracking: shrinkage fibre, mesh or both?

During drying the screed loses moisture and shrinks, a normal and unavoidable part of the hardening of cement-bound mortars. The problem is not the shrinkage itself, but the stress that builds up where the floor cannot shrink freely: at restrained edges, or on an insulation layer that moves unevenly. That stress is released as cracks. In the first hours after laying, plastic shrinkage caused by overly rapid evaporation also plays a role; how you control that early phase is covered in preventing plastic shrinkage cracks.

A related problem is curling: the edges lift when the top of the screed dries faster than the underside, most often with unbonded and floating screeds. Large floating areas therefore need movement joints or crack-inducer cuts. Within those bays, a fibre-reinforced screed limits plastic shrinkage cracking in the first hours and helps keep the cracks that do form narrower; joints, curing and a low water content do the rest.

How shrinkage fibre works

Shrinkage fibre consists of fine polypropylene fibres added to the mortar during mixing, which distribute themselves evenly throughout the entire volume, unlike crack-control mesh, which sits at one level in the floor. As soon as a micro-crack forms anywhere, the fibres bridge the crack faces on the spot. Cracks still occur, but as a rule stay narrower and less visible. A fibrillated micro fibre for sand cement screeds such as Profib contains around 100,000 fibres per kilogram, so the fibres are spread throughout the whole screed volume.

Fibre and mesh: complementary, not competitors

According to manufacturers, shrinkage fibre counts as secondary reinforcement: it does not replace crack-control mesh in every case, but reinforces its effect. The practical rules:

• Underfloor heating and floating screeds: adding fibre is standard here, because of thermal movement and an insulation layer that can move with the floor.

• Floating screed thinner than 65 mm: combine crack-control mesh with fibres; the mesh also copes with deformation of the insulation.

• Floating screed on firm, barely compressible insulation: fibre reinforcement alone can suffice.

• Screeds from around 60 mm: in Dutch practice, crack-control reinforcement is usually specified from about this thickness, mostly mesh supplemented with fibres; fibre alone can suffice only on a firm, barely compressible substrate.

Neither method prevents cracking completely; both limit the crack width, which is the difference between fine hairline cracks and wide, unsightly ones. Additional measures remain necessary: keeping the floor moist for the first few days, movement joints for large areas, and possibly shrinkage-reducing admixtures (SRA) as a supplementary measure, not a replacement. How the two compare in laying time and cost is set out in fibres versus mesh: time and cost. If it concerns a structural floor rather than a screed, macro fibres come into the picture; see when synthetic fibre concrete is the right choice.

Chape: the same floor, Belgian name

In Flanders the sand cement screed is called a chape (from the French chape de mortier). Technically there is no difference: a chape is also a semi-dry sand and cement mix spread as a finishing layer over the structural floor or insulation, with the same thicknesses, drying times and shrinkage issues. Anyone in Belgium ordering "chape with fibres" or "reinforced chape" therefore gets exactly this application: Dutch Fiber Trading supplies the same screed fibres to screed contractors in both the Netherlands and Belgium.

Which fibre do you choose for your screed?

For a sand cement screed, two micro fibres are relevant:

• Profib: fibrillated PP tape fibre, 12 mm, the standard fibre for sand cement screeds. Its branched structure anchors mechanically in the semi-dry mortar and distributes itself evenly. Dosage around 1 kg per m³ of mortar; supplied in 10 kg boxes, enough for about 10 m³ of mortar at that dosage.

• Promicro: monofilament PP micro fibre (12 mm, fibre class 1a to EN 14889-2) at 0.6–1.0 kg/m³, the choice when a finer surface quality matters alongside shrinkage control.

Torn between the two, or want to know how many boxes your project needs? The selection guide helps you choose in a few steps, the dosage guidelines for fibres list the dosage per application, or request a quotation directly with your area, thickness and floor build-up.