Cement screed (CT)
Cement screed (CT) - The basis for high-quality floor constructions
Cementitious screed, classified as CT (Cementitious Screed) in accordance with DIN EN 13813, is the proven standard in screed construction. Its defined robustness, versatility and tried-and-tested properties make it a technically sound solution for a wide range of applications in new builds and renovations. As a specialized specialist company, we have mastered the planning and precise execution of cement screeds for all requirements - a core competence of our company.
Composition and material properties
Cement screed is a mineral screed mortar whose quality depends largely on the quality of its components and the exact mixture. Whether mixed on the construction site or processed as a controlled factory dry mortar, the main components are:
- Binder: Standard-compliant cement (in accordance with DIN EN 197-1) as the basis for strength development.
- Aggregate: Quality-tested sand or gravel (in accordance with DIN EN 12620) with a defined grading curve for a dense grain structure.
- Mixing water: In precisely dosed quantities to control hydration and processing consistency - the water/cement ratio (w/c ratio) is a critical parameter here.
- Additives (optional): Used specifically to optimize specific properties such as workability, accelerated hardening or to meet special requirements (e.g. increased early strength, fibre reinforcement).
Curing is based on the hydration of the cement, which, when properly controlled, leads to a firm, highly resilient and durable screed structure. Its characteristic features are its high compressive and flexural tensile strength as well as its fundamental insensitivity to moisture once the equilibrium moisture content has been reached.
Areas of application for cement screed
The technical properties allow cement screed to be used in almost all construction segments:
- Residential construction: Reliable foundation in detached houses and apartment buildings, cellars, garages.
- Commercial and industrial construction: load-bearing surfaces in offices, sales rooms, warehouses, workshops - the choice of the correct strength class is crucial here.
- Public buildings: Durable solutions for schools, hospitals and administrative buildings.
- Damp rooms: Suitable for bathrooms, laundry rooms, wellness areas, where standard-compliant bonded waterproofing is essential.
- Heated floor constructions: Ideal as a heating screed for the efficient absorption and release of heat from underfloor heating systems.
- Universal substrate: Compatible with almost all common floor coverings - from tiles and parquet to resilient coverings and coatings.
Advantages of cement screed
- 💪 High strength: Ensures excellent compressive and flexural tensile strength for scheduled loads and safety reserves.
- 💧 Moisture resistance: Permanently resistant to the effects of moisture after complete drying out.
- Constructive versatility: Can be realized as a bonded screed, on a separating layer or as a floating screed on an insulating layer.
- 🌡️ Thermal properties: Good thermal conductivity predestines it for use as a heating screed.
- 💶 Cost-effectiveness: Offers a proven and solid price-performance ratio.
- 🔥 F ire protection: Meets the highest requirements as a non-combustible building material (class A1).
- ⏳ Longevity: An investment for decades if planned and executed professionally.
Technical properties and classification
The performance of a cement screed is clearly defined by its compressive strength (C = Compressive Strength) and flexural strength (F = Flexural Strength) in accordance with DIN EN 13813: CT-C[value]-F[value].
- CT: Cementitious Screed
- C[value]: Characteristic value of the compressive strength class (e.g. C25 ≥ 25 N/mm²)
- F[value]: Characteristic value of the bending tensile strength class (e.g. F5 ≥ 5 N/mm²)
The selection of the standard-compliant strength class according to the subsequent use and load is a fundamental planning task.
Overview of common strength classes:
| Screed class | Minimum compressive strength (N/mm²) | Minimum bending tensile strength (N/mm²) | Typical application examples |
|---|---|---|---|
| CT-C20-F4 | 20 | 4 | Residential construction (lower burden) |
| CT-C25-F5 | 25 | 5 | Standard residential construction, offices, public areas |
| CT-C30-F5 | 30 | 5 | Commercial areas (medium load) |
| CT-C35-F6 | 35 | 6 | Areas with higher loads, light industry |
| CT-C40-F7 | 40 | 7 | Industry, high point loads |
| Higher classes | as required | as required | Special industrial applications |
ℹ️ Note: Correct dimensioning and determination of the screed class is essential for suitability for use and freedom from damage. It is the responsibility of qualified planners or the specialist company carrying out the work.
Processing and drying time
The quality of the finished screed stands and falls with precise adherence to all processing steps:
- Substrate testing and preparation: the foundation for a functioning construction.
- Mixing: Strict control of the water/cement ratio and uniform homogenization.
- Application and distribution: Professional placement at the correct height.
- Careful compaction: Indispensable for achieving the planned pore structure and final strength.
- Exact stripping and surface finish: guarantee of evenness in accordance with DIN 18202 - tolerances are not recommendations.
- Controlled post-treatment: protection against premature dehydration (draughts, heat) to ensure optimum hydration.
The drying time to readiness for covering is a material-specific property of the cement screed ❌ and requires patience and specialist knowledge. It is influenced by:
- Screed thickness (decisive factor)
- Ambient climate (temperature, relative humidity)
- Ventilation options
- Type of cement and any additives
The rule of thumb (~1 week/cm) serves as a rough guide, but in no way replaces professional assessment. ⚠️ The floor may only be approved for covering once the residual moisture required by the standard has been reached, as verified by reliable CM moisture measurement. Premature covering will inevitably lead to serious and costly damage to the top layer and the screed structure.
Variants of the cement screed
Different types of construction are used, tailored to the specific technical and building physics requirements:
- Bonded screed: For the highest mechanical loads with direct, friction-locked connection to the load-bearing concrete.
- Screed on separating layer: Allows movement in relation to the substrate, separated by a suitable intermediate layer.
- Floating screed (screed on insulation layer): Standard for thermal and impact sound insulation in building construction, structurally separated from all adjacent building components.
- Heating screed: Designed as a floating screed to accommodate underfloor heating pipes.
- Rapid screed: Special form with accelerated hardening and drying for time-critical projects (special binders/additives).
Professional execution - our benchmark
The durability and functionality of a cement screed are the direct result of flawless craftsmanship and the use of high-quality materials. The indispensable pillars of our quality work are:
- Strict compliance with all relevant standards and regulations (in particular DIN 18560, DIN EN 13813, DIN 18202).
- Careful selection of materials and precise adherence to the recipe.
- Mastery of processing techniques from compaction to surface design.
- Guarantee of the required evenness tolerances as a basis for the top layer.
- Consistent post-treatment and monitoring of drying conditions.
- Responsible implementation and documentation of the CM measurement.
Commissioning an experienced and specialized screed company like ours is the best guarantee that these decisive quality criteria will be met without compromise - for a solid, level and durable foundation for your floor.
Frequently asked questions (FAQ)
It often takes 4 to 8 weeks, sometimes longer - depending on thickness and climate. Never rely on estimates! CM measurement by a specialist company is the only reliable proof of the required residual moisture.
The screed costs per square meter vary greatly (thickness, type of structure, area, etc.). However, cement screed is often the most economical option for a solid screed. An individual offer is necessary.
Yes, it is very well suited and proven as a heating screed. It is important that the pipes are covered correctly and that the heating protocol complies with standards before covering.
Perhaps for very small, uncritical areas. For living areas or underfloor heating, a screed-laying specialist is strongly recommended for quality, evenness and compliance with standards in order to avoid damage later on.
This is a standard class: CT = cement screed. C25 = minimum compressive strength 25 N/mm². F4 = minimum flexural strength 4 N/mm². Sufficient for most living areas.