In order to install/anchor a new toilet flange correctly I plan to pour cement to fill in the space between the drain and the existing concrete. This should prevent toilet leak from entering below the tile and slab.
1. Since the ABS turn is visible and only partially under concrete, can I pour concrete directly on to of the ABS? Or should I put a layer of sand in between?
2. For concrete, which type should I use?
Hydraulic cement? Anchoring cement? Quick-drying?
Anchoring cement would seem to be the best choice to hold down the flange bolts but I'm concerned about its expansion properties putting pressure on the ABS turn.