English to French Tech/Engineering Construction / Civil Engineering Tuyauterie

From specifications for the drainage system of a new building:

INSTALLING RODDING POINTS
- Bedding and surround:
- Material: Concrete (general).
- Thickness (minimum): 100 mm.
- Permissible deviation in level of external covers and gratings: +0 to -6 mm.


I found this for example: http://www.marleyplumbinganddrainage.com/support-and-advice/...
I also found some photos. But I can't find anything in French and have no idea what the French term is!! Thank you.