I have a patio area round my house in Italy, the tiles are laid on a concrete base, with originally a thick layer of sand (there are rooms below the patio), and some kind of adhesive. The sand is disappearing, tiles are coming loose and are cracking. Lifting some of the worst tiles I can see there is hardly anything left holding them. Most of the area still seems sound.
My questions are these:
1) I would like to lift and re-secure the tiles I know are less supported - should I use sand and adhesive, just adhesive (easier for me - a novice), or something else?
2) Should I be taking the weather into consideration? (Hot summers, prolonged heavy rain in winter, 15 degree C. temperature drop between day and night in winter)
3) I would like to re-grout the whole are (after patching up) to seal it, would it be sufficient to grout over what's there without taking out the grout? Much of the grout still seems sound.
Any advice greatly appreciated.