Homeowner's husband tried a DIY method for installing tile. Used pre-mixed mastic instead of thin-set mortar to set tile in their shower pan. This isn't a good idea to use this product in a "wet area" as the material re-activates and thus spawns a gooey swamp of movement underneath.
Needless to say, that had to get ripped out during demolition, wherein, found another problem, underneath. The pitch in pan was improper, was not waterproofed, and constructed rather unsound.
So we came in to band-aid and remedy the situation.
Tore down the first couple courses of wall tile. Installed new cement backerboard and Schluter Kerdi membrane (for waterproofing.)
Then, a mud shower pan was constructed over plywood subfloor.
First, covered with building paper and stapled metal lathe. Portland cement and sand mixed for mud material and sloped to quarter inch per foot standard towards drain flange. We allow 3 days for mud to wick, and once cured, apply 2 and a half coats of waterproofing membrane over the new substrate and up the wall.
Dimensions of the shower were bumped out larger in design process to accomodate installation of tub inside shower.