On 28/10/2020 13:57, fred wrote:
Is this an ok solution to a leaking shower tray? The tray has an upstand lip but the tiler elected to start full tiles above this lip and used a cut tile beneath it to bridge the gap. The result is the grouting between this short tile and the full size on above it is prone to failure and water leaks behind it and behind the upstand. I just wondered if mastic would be a better alternative to more grout

It's normal to use cut tiles around edges because then they can be cut
to accommodate edges that aren't level or straight. You could put
another tile over the top, starting part-way down the previous one.