Hello, I am currently renovating a 1920s house. At some point in time the underfloor void has been filled with concrete, wooden joists been laid within it, and topped with bitumen. After a lot of hard work we have managed to get the joists out in order to use the channels for new plumbing and electrics. Eventually we were planning to use a bitumen friendly self-levelling latex, but we were unsure as to whether filling the channels with concrete would be do-able with the bitumen sitting below it. Any advice? Cheers in advance