Happy New Year to all! I have a large outdoor gazebo raised cement slab at least 20 x 20 feet. I have no expansion joints but I do have a nice crack in my slab. I want to tile over the slab. I know I need to use ditra but how or should I fix the crack and it was suggested to use porcelain tile? Any suggestions with type of tile. Live in Charlotte NC some freezing occurs. I think crack is due in proper slab installation and also last 2 years we have had draught conditions so clay soil was shifting. Any suggestions would be appreciated. Harry I did view your outdoor installations.

Has the slab shifted or separated in a vertical direction or just horizontally?

Normally, nothing needs to be done to the slab if Ditra is being applied, however Ditra can not save you from any vertical movement.

look into Quartzite Stone. Looks a lot like slate, but is much tougher. Some places have it labeled as slate. Like RC said, vertical displacement is not ok, but horizontal separation of about 1/8" is normal in slabs and ok to cover