Poorly done, below grade, custom shower pan
resulted in moldy, rotten enclosure. Existing drain
needs to be replaced for new tile work, so I roto-hammered out my slab around the drain last night, intending to replace it.
When I removed the rubble, I found a (now damaged) black plastic sheet between the slab and the soil beneath (I've already removed the old shower pan, so this is not the waterproof membrane in the pan, but, in fact, beneath the slab itself). I haven't read anything about laying plastic before pouring a slab, but it wouldn't be the first unusual construction quirk I've discovered with this place. So;
1. Assuming I need to replace the plastic at all, to what lengths do I need to go to seal it? In other words I guess: Do I need to tear out more of the slab and seal the existing plastic with undamaged plastic?
2. Is it necessary to shape the broken concrete in any way before pouring the new concrete? (I've heard a few different things like making the top of the opening smaller than the bottom)
3. I realize I'll need sand and Portland for the shower pan, but will Quikcrete work for replacing the busted portion of the slab?
4. Anything else I should consider?
Sure appreciate any responses