Gap in tiles and shower tray of appx. half and inch

Sounds to me like the shower tray hasnt been fittted properly ,if the walls where out of square they should have been chopped away to make the shower tray butt up better then tiled down to the tray so there is no gap , then silicone round the shower tray and up the corners. The only thing you can do now ,besides ripping out and redoing the lot, is get yourself some plastic quadrant and fit that,over the adhesive he has used. You could also just re-silicone round over the adhesive and try it see if it leaks. Please note that it is also difficult to give accurate advise without seeing the tray .

Hi The shower tray should have been fitted as close to the brick/timber wall, the tiles should ideally sit on top of the shower tray and the plumber in my experience should have fitted a tanking kit. you are likely to get leakage and mold. would rip out and start again with someone who knows what they are doing! Graham Collum Property Services

That's a big gap to fill with adhesive, sounds like a mis measure during installation actually. If its a good quality sealant it should hold, but movement in the tray will eventually lead to the seal having to be replaced over time. Would have been better to either raise the height of the tray