Strip the old grout and silicone out
All wall and floor grout in the shower ground out, junctions and corners cut back, waste and tap penetrations opened up. This is where nearly every leak actually is.
Seal the substrate through the tile joints
A penetrating sealer is flooded into the joints and drawn into the bed underneath, so the layer that was letting water through is sealed without lifting a tile.
Re-grout in epoxy, not cement
Epoxy grout doesn’t absorb water and doesn’t grow mould in it. It’s harder to work with, which is why most jobs use cement grout, and why most jobs are back in seven years.
Junctions, screen, flood test, warranty
Neutral-cure silicone to all changes of plane, the screen re-bedded, then the shower is flood-tested and the ten-year warranty issued. Usable again after 24 hours.