Concrete Toppings
Structural concrete topping
The concrete topping thickness and reinforcement specification shall be determined in accordance with BS EN 1992-1-1⁸ by a qualified structural engineer
The concrete topping shall be according to BS 8500-1¹¹, BS 8500-2¹² and BS EN 206¹⁰, manufactured in plants covered by the QSRMC scheme (Quality Scheme for Ready Mixed Concrete) and laid by personnel with the appropriate skills and experience;
The specifications in Table 2 are suitable for single-family self-contained dwelling units and communal areas in blocks of flats with the characteristic imposed loads defined in Table 4;
The concrete specifications in Table 3 are suitable for commercial buildings with the characteristic imposed loads defined in Table 5.
*NOTE: NHBC do not accept micro-fibre structural concrete toppings
Table 2 – Concrete topping specifications for single-family self-contained dwelling with the characteristic imposed loads given in Table 4
| Overall concrete thickness above the services (mm) | Grade | Maximum aggregate size (mm) | Type See also NHBC | Reinforcement Specifications³⁰ |
| 65-75 | C28/35 | 10 | Self-compacting micro-fibre* (Class I) | Fibrin XT Ultra (0.9 kg/m³), Fibrin 23 (0.9 kg/m³); or similar approved |
| 65-75 | C28/35 | 10 | Self-compacting macro-fibre (Class II) | Durus S400 (4.0 kg/m³) Novomesh B&BA (macro, 3.33 kg/m³), Durus Easy Finish (3.0 kg/m³); or similar approved |
| 65-75 | C25/30 | 20 | Standard micro-fibre* (Class I) | Fibrin XT Ultra (0.9 kg/m³), Fibrin 23 (0.9 kg/m³); or similar approved |
| 65-75 | C25/30 | 20 | Standard macro-fibre (Class II) | Durus S400 (4.0 kg/m³) Novomesh B&BA (macro, 3.33 kg/m³), Durus Easy Finish (3.0 kg/m³); or similar approved |
| 65-75 | C25/30
C28/35 | 20 Standard
10 Self-compacting | Conventional | 1 layer of A142 steel mesh to BS 4483 with a characteristic yield strength of (fyk) 500 N/mm²; nominal cover to reinforcement shall be 35 mm |
| 65-75 | C25/30
C28/35 | 20 Standard
10 Self-compacting | Steel Fibre | Adfil SF86 (13.33 kg/m³), Novomesh B&BA (steel, 15.0 kg/m²); or similar approved |
Table 3 – Concrete topping specifications for commercial buildings with the characteristic imposed loads given in Table 5
| Thickness (mm) | Grade | Maximum aggregate size (mm) | Type | Reinforcement |
| 65-75 | C25/30 | 10 | Self-levelling self-compacting concrete | Steel mesh1) |
| 65-75 | C28/35 | 20 | Conventional | Steel mesh1) |
1) Structural mesh should be sized and designed according to BS EN 1990⁵, BS 1991-1-1⁷ and BS EN 1992-1-1⁸ and their UK National Annexes
Table 4 – Imposed and partition loads for concrete topping reinforced with macro-polymer fibres and steel mesh A142 (kPa)
| Description | Characteristic value of loads for single-family dwellings | Characteristic value of loads for communal areas in blocks of flats |
| Imposed uniformly distributed load (kPa) | 1.5 | 3.0 |
| Imposed concentrated load (kN) | 2.0 | 4.0 |
| Line load partition, parallel and perpendicular to the beam (kN/m) | 4.0 | 5.0 |
| Allowance for moveable partition (kPa) | 1.0 | 1.0 |
Table 5 – Imposed and partition loads for commercial buildings and concrete topping reinforced with steel mesh
| Description | Characteristic values of loads |
| Imposed UDL (kPa) Imposed concentrated load (kN) | 5.0 4.5 |
| Line load partition parallel and perpendicular to the beam (kN/m) | 5.0 |
| Allowance for moveable partition (kPa) | 1.0 |
