Incorrect tile grout used.
Tiles falling off wall tile adhesive.
Use a piece of cloth to remove any adhesive that is displaced above the tiles.
Then prep the wall and use the adhesive made specifically for the tile you have.
Thinset is best adhesive.
Make sure that the tile adhesive that you use is water resistant.
How do you fix it.
Apply grout around the tile on the gaps between the tiles.
Was the adhesive left on the wall for too long before you placed the tiles.
This in conjunction with skinned over adhesive is the root cause of your tile failure.
The adhesive needs to be applied evenly and on every tile.
Be sure to spray the wall surface with water to activate the glue.
Tile falls off wall organic glue skins over.
Clean off the old stuff from the back of the tile and from the wall.
Use gorilla glue to replace each one.
Make sure that the tile is level with the existing tiles so that you don t end up with ridges.
If water gets behind the tiles and in the grout mildew can grow and it will cause the adhesive to deteriorate.
This means it is thick enough to easily bridge differences between the two mating surfaces.
Press the new tile down over the adhesives you have just applied.
Many people strip the loose tiles sand them and reposition with new adhesive.
The wall surface could have been irregular with humps and dips in it.
Give the adhesives 24 hours to set.
Though more common in an older home rogue tiles can be found in new homes as well.
Over time the mortar holding a wall tile may fail to do its job letting a tile become loose and fall.
Grouting has been done too early.
This is not just a threat for your tiles but also for your health.
Use a glue that is gap filling.
Make sure that they don t come into contact with any water during this period.
If no adhesive is applied then the tiles will fall off.
Lloyd s bathroom tiles failed when either the wall wasn t prepared properly or the mastic was exposed to too much.
You should leave the tile adhesive to set for at least 24 hours before grouting the tiles.
Or take them all down putting wax paper between each tile so they don t get damaged.
Otherwise the repair may not hold and the tile may also sit a little higher than the ones next to it.
As ceramic tile gets larger the wall or floor surface must be flatter and flatter.