Hi, I have a leaking shower from the seal around the shower tray. The plumber who installed it siliconed between the tray and the OSB wooden board behind it and then used a sticky rubber seal on the tray and then on to the wall. This was then tiled over and silicone used from the bottom tile onto the tray. Water got in and I have jhd to remove 4 rows of tiles within the cubicle. Should the rubber seal be put on under the tiles or should it go on top of the tiles . Thanks Joe 