This was a badly tiled tray that was letting water through the joints, the tiles were a mixture of dot and dab and using a notched trowel. There were big voids around the drain that water was sitting in and the tiles eventually came loose. I suspect that the drain had been set too high and they had to build up adhesive to the correct height.
Thanks for that, John. I've been on my hands and knees and now in daylight I can see that there are extremely fine cracks along joints in the shower, mostly where the grout meets the tiles. They are very difficult to see, but definitely there, plus gaps around the grout round the drain. I suspect this is what is happening in my tray. One question, though: if we take up the tiles, will this damage the Impey tanking underneath?
All this has been very helpful, and certainly made me look a lot more closely at what is going on with the grout, so thanks everyone who has replied!
Paula
Only thing I could do was remove the tiles, fill the voids, and then use a notched trowel, back butter the tiles, fix and grout, and no more problems.
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