I will soon pour a mortar pre-slope on a concrete slab. Regarding a barrier between the two; some of the research I’ve done suggest using felt/tar paper and some suggest using thinset. Any suggestions? The city's plumbing inspector doesn't care, he said it's my choice.
The cement board on the right and left are not yet screwed it; they will be removed prior to the pre-slope pour. The black sticks are pre-slope sticks which I may or may not use.
Thanks to all,