Hi everyone, I had a leak in my CH pipes running through my kitchen. Pipes have been replaced - not only the damaged section, but we ran new pipes up to the radiator as it turns out when this radiator was installed last year, the flooring guys filled the channel with concrete. My concern was this meant no room for pipes to move or expand, so to avoid potential future issues due to this, we layed new pipes around and to the rad. Now, to avoid repeat errors concerning filling the channel, I need to know what to use to fill the this around the pipes, then put a layer of concrete on top (the floor is concrete) then reapply the karndean/antico flooring. So my question is what to use to fill the channel around the pipes before the concrete goes on top? The plumber suggested embedding the pipes in sharp sand, then a layer of shingle on top, then the concrete layer on top of that. Looking online it seems there are conflicting theories - I just want to know if the above is a valid option, or others that be be equally valid and correct.