Background:
I've moved into a house 3 months ago that I have been renovating for a while. I have done a lot of the work myself but I left my builder to do the plumbing and tiling while I was away for work.

If I spray the tiles in the shower for 5 mintues, water starts tricking out from behind the shower tray.

If I just run the shower into multiple buckets then no leak occurs so it can't be the pipes or the waste.
I have uploaded pictures [here](https://drive.google.com/folderview?id=0B7kuw9HZDyuFMG4yMVVwVnFuZkE&usp=sharing)
(You can see the shower tray is not flush with the wall)
I re-siliconed around the tray / tile boundary and I tried a grout sealer which seemed to stop the problem for a few weeks but now the issue is back again.

I know he tiled straight onto green plasterboard and used Bal Micromax 2 grout.

1. Do you think the grout has failed? Would this happen if we did not let the grout cure for long enough? How long is not long enough?
2. Should I expect the grout to be waterproof? If not is their waterproof gout on the market?
3. Would removing the grout and re-grouting fix the problem?

I also thought about removing the bottom row of tiles and trying to reseat the try against the wall but I am not sure that will help either... 

He was a nice guy so I am sure this is how he always does it and I know he has done 50+ jobs without issue (unfortunately he has moved country so I have lost contact with him and cant even bounce some ideas off him to troubleshoot)