Allowance in design for deviation for the nominal cover of concrete cast against uneven surfaces: the values of k1 and k2
Eurocode 2 part 1-1: Design of concrete structures 18.104.22.168 (4)
For concrete cast against uneven surfaces, the minimum cover should generally be increased by allowing larger deviations in design. The increase should comply with the difference caused by the unevenness, but the minimum cover should be at least k1 mm for concrete cast against prepared ground (including blinding) and k2 mm for concrete cast directly against soil. The cover to the reinforcement for any surface feature, such as ribbed finishes or exposed aggregate, should also be increased to take account of the uneven surface (see § 22.214.171.124 (11)).
The recommended values of k1 and k2 for concrete cast against uneven surfaces are 40 mm and 75 mm respectively.