Concrete screed for commercial buildings: leveling, insulation, flatness

Concrete screed addresses two distinct configurations in commercial real estate. In new construction, the reinforced screed enhances the floor’s thermal and acoustic insulation, with an insulation target of 28 to 45 dB depending on the room’s use. In renovation, it corrects level differences and flattens surfaces before laying the finishing floor coverings.

Three standards structure the specification:

• Product standard: mechanical characteristics and resistance classes of screeds.
• DTU: traditional screeds based on hydraulic binders.
• DTU: fluid screeds based on cement or calcium sulfate.

Technical arbitration relies on flatness measurement with a 2 m straightedge. A self-leveling compound with a Technical Approval is suitable for deviations below 10 mm. Beyond 20 mm, the DTU liquid screed or the DTU mesh-reinforced screed become necessary. The 7 mm under a 2 m straightedge rule comes directly from the DTU (art. 6.3): beyond that, large-format tiling or epoxy resin are disqualified. On a floor fitted with a raised access floor of 100 to 300 mm, the tolerance tightens to less than 5 mm to avoid individually shimming the jacks.

Our reading diverges from the industry orthodoxy on this point: the near-automatic specification of a DTU liquid screed as soon as a deviation exceeds 10 mm often reflects a general contractor’s reflex rather than a technical arbitration grounded in the floor’s actual constraints. On a floor under 300 m² with deviations below 5 mm and a flexible LVT vinyl covering, a 3 mm fiber leveling compound is sufficient and the liquid screed adds 3 to 5 weeks to the schedule. Likewise, above the 8th floor in a high-rise building, lightweight infill should be preferred whenever the load distribution leaves less than 80 kg/m² available: a 6 cm reinforced screed at 130 kg/m² then saturates the structural reserve.

For the CFO and Asset Manager: what the screed really weighs on the schedule and the rent avoided

For the commercial decision-maker, the subject is not technical, it is financial. A DTU reinforced screed requires one week of drying per centimeter of thickness: six centimeters equal six weeks of unproductive floor space before laying the covering. On a Parisian commercial asset in the Central Business District, each week of delivery delay represents a significant deferred occupancy cost, varying by location and asset quality. Over 1,200 m², six weeks represent an order of magnitude of 60,000 to 180,000 EUR in deferred rent.

The arbitration between DTU liquid screed and DTU cement screed must therefore be examined in cash-flow terms, not in the technical specifications. The liquid screed appreciably reduces drying time under controlled hygrometry, at the cost of additional pump and mixer-truck mobilization. The observed tipping rule: below roughly 200 m² per continuous pouring zone, the mobilization surcharge tends to cancel the time gain. Above 1,500 m² in a single span, the liquid screed regains the advantage, with daily output rising from 200 to 400 m²/day.

For the Asset Manager steering a commercial decarbonization trajectory, the screed incorporating a low-temperature underfloor heating system compatible with RE2020 falls within the -40% trajectory by 2030. For the CFO arbitrating a CAPEX, self-leveling compound remains far less costly than a full reinforced screed: the preliminary diagnosis is not a cost, it is what prevents switching to the wrong solution.

The Kytom method in 4 steps: diagnosis, structure, substrate, drying

The method formalized by Kytom unfolds in four steps, carried out by the project managers of the regional offices.

1. Technical visit and arbitration: survey of high and low points, choice between self-leveling compound, liquid screed or reinforced screed depending on the measured deviations.
2. Structure verification: load distribution with a structural engineering firm to confirm compatibility with the 250 kg/m² admissible in category B (office use). A 6 cm reinforced screed adds 130 kg/m², a threshold to factor into the calculation. Any overload greater than 5 cm is subject to written validation.
3. Substrate preparation: complete dust removal, bonding primer suited to the chosen binder, in accordance with the applicable DTUs.
4. Implementation and drying control: infill, floating or compression screed depending on the case, possible integration of low-temperature underfloor heating whose ambient conditions are monitored by a temperature/hygrometry probe (range 10 to 40°C and 20 to 90%RH, hygrometry MPE +/-5%) installed at 1.5 m height on an interior wall.

The carbide-bomb hygrometric control sets the thresholds before laying: 4.5% residual moisture for vinyl flooring, 3% for bonded parquet. A cement screed requires one week of drying per centimeter of thickness. MEP coordination beneath the raised access floor (air distribution, high-current power, IT cabling, condensate drainage) is synchronized on a single schedule managed by the project manager.

Note: the 4.5% hygrometric threshold for vinyl flooring corresponds to a national average, but in the North and East regions between November and February, actual drying can significantly exceed the one-week-per-centimeter rule despite regulatory compliance. The schedule must factor in this seasonality: a January delivery on a 6 cm cement screed is planned with 9 weeks of drying, not 6.

Results observed on Kytom projects: compliance, acoustic gain, durability

Kytom projects involving screed redos reveal three concrete benefits.

• Laying compliance: rigorous substrate preparation significantly reduces post-handover rework on tiling, resin, vinyl flooring and carpet tiles.
• Acoustic gain: combining a reinforced screed with a resilient underlay appreciably improves airborne sound insulation between floors, in accordance with the requirements of NF S31-074.
• Durability: no structural defect has been observed on the projects delivered and monitored after handover.