Have done a few repair jobs similar to yours,
If possible I like to leave a gap of about 5mm around the tray, tank down past the top of the tray(use a float or, even better tank before tray is fitted)and then fill the gap with lots of Silicon,the tile will cover this,and then a neat bead of Silicon after it's tiled
Much better to stand movement to tray than a thin bead of Silicon or tape
Your client should be able to make a claim on his house insurance to cover the repair by the way
If possible I like to leave a gap of about 5mm around the tray, tank down past the top of the tray(use a float or, even better tank before tray is fitted)and then fill the gap with lots of Silicon,the tile will cover this,and then a neat bead of Silicon after it's tiled
Much better to stand movement to tray than a thin bead of Silicon or tape
Your client should be able to make a claim on his house insurance to cover the repair by the way