Leaking coram watergard shower tray in stud alcove


I have had two Coram waterguard shower trays installed as part of an extension. The showers have leaked two or three times. I have sealed everything as best I can and identified the main cause to be the grout above the first row of tiles.
When I bought the trays I phoned coram customer support and was advised that part of the wall should be chased out to allow the tray to fit in my alcove. The alcove consisted of a dry lined wall and two stud partitions with plastered plaster board, the problem seems to be that the tray flexes and cracks the grout above the first row of 4" by 8" tiles which overlap the tray. The water gets inside this crack and runs down behind the tray through the floor and through the ceiling below. I can only reach the front three legs but it would appear that they might loosen (unscrew) with repeated use of the shower.
The tray fits in the alcove between the wood of the studwork but doesn't have plasterboard against each side.
What do you suggest?
I am considering using mastic instead of grout above the first row of tiles, trying to fix the legs so they can't spin with mastic/a screw (??) or using a row of larger tiles above the tray such as the 12 inch floor tiles I have in the bathroom.
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"anon" wrote:

Unless you can cure the flexing I suspect that whatever you put in the gap between the first and second row of tiles will fail sooner or later due to movement and moisture. But it is worth trying fixing the legs and removing the grout, replacing it with a silicone sealant. Transparent waterproof tape may prevent water entry but may not be visually attractive. Acrylic baths also suffer from flexing which can be prevented by standing the bath on a wooden frame to support the bath edges.
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Hi,
I have a similar setup here, If I remember rightly (its been a while) the big yellow feet of the tray had holes drilled in them for securing screws to prevent any creep or unscrewing. You dont say what size the tray is - but the 760mm tray I had from these people. (http://www.plumbworld.co.uk/55-1971 Nice diagram of the feet there too ) hasnt moved and cracked the gout with me using it for over a year now. Im also pretty sure I *DIDN'T* stick the tile to the shower tray, but stopped at the wall level allowing the tiles to hang over just resting on the tray lip, then grouted the sides and siliconed the bottom.
Not sure if thats any help...
Lard.
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Thanks, unfortunately the builder tiled under the tray so i I will have problems drilling through the tile to screw. I could drill through the legs and screw in however I can only reach the front three legs easilly.
:(
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