I was removing old tile from my kitchen and found the crack seen in the pictures. I was wondering how big a deal the crack was and how to proceed with trying to lay new tile. I wanted to knock out more of the thinset mortar left around it, but I was afraid I might make the crack worse. Any advice on how to go forward?
You'll need to lay down an isolation pad over the crack before installing the new tile.
The pad will allow the crack to open (if it is active) and not break the tile like as if they were set directly to the concrete floor.