The Matki shower enclosure in my 18th century house was fitted a year ago and there is significant leakage through the grout between the tiles. There is quite a lot of movement in the floor and walls of this first floor bathroom and our builder is suggesting digging out the existing grout and replacing it with flexible grout. Our plumber on the other hand is saying that the movement means that this will never work and that to solve the problem once and for all it will be necessary to replace the tiles with acrylic (?) sheeting, which is clearly a major job. Does anyone have any advice please?
The movement in the floor will be the problem, once someone gets into the shower the shower tray may move a little and open up the gap between the shower tray and the tiles.
When fitting a bath - you need to fill the bath with water whilst tiling. Then you tile right down to the bath, this allows for the movement when the bath is full.
I would do the same with the shower tray (if possible) when re-grouting using a flexible grout stand something in the shower that will simulate a similar weight to someone in the shower - then when the grout has set it will allow for that flexibility and movement.