fred wrote in
:

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

Sealant rather than mastic works well but it needs to be sanitary silicone
as it has additives which discourages mould growth. I have tried the
proprietary more sticky sealants to overcome the creeping gap problem but
they became discoloured in the longer term.