Filling up a channel in the slab

[TeaAndBiscuits]

Hi all,

I'm redoing my ground floor bathroom. It has a solid floor - concrete slab, 75mm polystyrene insulation and then screed.

I've dug out the old soil pipe which was partially recessed in the slab in a sort of channel/trench that looks like it was cast into the concrete when it was poured.





I'm going to be having a stub stack right in the corner and then just the single 40mm waste running down one side of the trench as in the picture.

My question is - what should I fill the rest of the channel/trench with before recovering with insulation and screed? Sand? some sort of aggregate? or do I need to use actual concrete?

Ta

 

[bobasd]

you could make up a rough mix of semi dry sand cement and stones.
maybe get the mods to transfer your post to the plumbing forum.