Last year we had a contractor remodel our master bathroom. The grout is cracking on the shower bench. When the contractor's helper came to repair the grout, he removed the cracking grout and the four tiles the grout had been surrounding fell off. The mortar was no longer holding them in place. I could see mold on the surface that the tiles had been attached to. It appears the tiles were attached to basic drywall material, not cement board or greenboard. Looking at old photos from the construction phase, it appears the cement board was only used on the shower floor, bench front, and bench seat not the shower walls or bench back.
I've been researching the proper installation ****** now. It seems they were supposed to use cement board and waterproof liner under the tiles on the shower walls and the entire bench rather than drywall.
Can this problem be easily fixed? Should I repair the obviously loose bad spots and hope no further damage occurs? Does the shower need to be completely torn out and redone? Please help. I no longer trust my contractor to tell me how this can be fixed properly.