Graham. wrote:
Unless the user is very careful indeed, water is dripping
through the bathroom floor/kitchen ceiling.
The bottom partial tiles were lose, being held only
by the bead of silicone sealant.
http://myweb.tiscali.co.uk/infoweb/shower.jpg
What little plaster was left intact I have chipped
away leaving this gap. What is the best way to
proceed? Is there something waterproof I should
be using to fill the void, and will this be the same
product that fixes the tiles back?

Difficult one. You probably know that ideally you should pull off more
or all the tiles and replace the backing board (this scenario is exactly
why I favour using more expensive waterproof board like Aquapanel,
rather than plasterboard as has been used here by the looks of things.

How secure are the tiles above the gap? Isn't the board mushed there too?

I think it will be very hard to effect a decent bodge-type repair here
which doesn't leak - you need to create a really rigid surface in that
tiny gap which you can fix tiles to.

I wonder whether the best solution would be to fix a single row of new
tiles (white, to blend with the tray) around the whole perimeter of the
tray and covering the gap, a bit like a skirting board?

David