My previous kitchen tiles were laid on top on wire mesh and mortar. Except for a few smaller grout cracks they were relatively okay and flat. After removing the tiles, mortar, and mesh I have discovered that the plywood is sagging/flexing in some areas which I will try to fix by securing it with screws.
However, as per underlayment, I am not sure if I should go again with wire mesh or Ditra would be a better option when it comes to preventing possible cracks?
Best Answer
"Except for a few smaller grout cracks they were relatively okay and flat"; Ditra is primarily a water blocking membrane. If you believe that the "sagging/flexing plywood" was caused by water penetration, then an upgrade to the water resistance of your assembly is in order.
However, mortar and mesh provide a function unrelated to Ditra; it is to provide a strong and flat substrate to support the tile installation.
I recommend both! Ditra to waterproof the plywood, then cement tile-board or a mortar bed to provide a strong surface to place your tile on.