shower rebuild

[Tim K]

Need some help. Redoing a shower that is 4'x6 1/2'. The old shower pan looks like it's made of quickcrete concrete. The liner is flat on the plywood, about 1 3/4" layer then wire lath, then aobut another 1 1/2" of concrete, all over a sunken wooden box. Shower is wheel chair accesable. I chilsed out about a 12" circle around the drain. Am planing to install kerdi drain and membrane. The adjoining bathroom floor is level with the shower floor, but there is only one layer of 3/4 over the joist. Will be putting in an heated tile floor with detra, so will be adding another layer of 5/8 over the existing 3/4. I want to keep the shower floor and bathroom floor the same height. The deflection is good, and the box is supported well. The tiles were installed on the walls and floor with what looks like mastic of some sort, which by the way, was realllllll easy to remove. got behind one, and about 3 or for others fell off. Long way to ask a question, but needed to get you some info first. The question is
1: can I lay a drypack over the existing shower pan? The old slop is good. Would be adding about 1" over the entire shower pan, then kerdi with their drain.
2: Would doing a skim coat of modified over the old pan before the mud pack help it stick? and is 1" too thin, and would it crack back out.
3: Or would it be best to take out the old pan and start over?

[TileArt1]

Hi Tim,

In my opinion, it is always better to tear everything out and start fresh. That being said, it is not necessary, just the way I prefer it.
If you do go over it, yes, skim coat it first. 1" is thick enough to be solid. This is providing, of course, that the present pan is good and solid. Your pan will only be as solid as what is beneath it.

[Tim K]

It is solid, took me almost 1 1/2 hours to air chisle around the drain. I am leaning toward tearing out the whole thing, but am looking at almost another day in tear out. The concrete is REALLY hard. Thanks for the advise.