Initially, the wall tiles were installed too high off the shower floor so if floor tiles were installed, there would be a gap at the bottom of the wall tiles to top of the floor tiles.
I hired a company that installed a second mud pan on top of the existing mud pan in order to thin set the floor tiles to cover the gap below the wall tiles. They had scored the mud pan with a grinder to install the second mud pan on top of the first. Then the porcelain tiles were laid on top of the second mud pan with thin set.
Years later the grout washed out from the shower tiles at one end of the shower, lifting several tiles up from the shower floor. I elevated the raised shower floor tiles from that section of the shower floor and was able to remove them. Then I scooped up and scraped up the second mud pan off the first mud pan. The first mud pan was completely hard and not disturbed.
Now I need to fix the shower floor so we can use the shower again. I am wondering what product to use to reinstall those shower floor tiles. I need to establish a bed of about 1 to 2 inches to get them at the proper elevation, so they will be level at the height of the 2/3 remaining shower floor.
Thin set could be used as a second step to adhere the tiles, but I can't build up to that thickness using just thin set. What should I be using to raise the mud pan about 1-2 inches?
How can I achieve a strong bond to the first mud pan besides relying on just the scoring that was done with a grinder, which I have now cleaned out?