This photo is of a new floor this business had installed. The installer never removed any of the old tiles which were even loose. There was one bad section in particular that was 102 tiles. We removed the new tiles and removed the old tiles underneithe then added floor leveler just under the 1/8 tile thickness. We then replace this section with new tiles as seen in the bottom photo.

Photo of the old tiles left under the new.

More photos of the old tiles under the new.

They were 5 layers thick in spots and not stuck.

This Is a photo from the  section we had to remove. The white area was where there used to be a wall. There was a 1/4 drop in this section the contractor just installed the tile over which was cracking. We took up the whole section and leveled it so there it ended up as one level

This photo is of the floor after we replaced the tile over the whole and section we repaired.