After install a new shower/bath mixer, I am proceeding to restore waterproofing behind the mixer follow by the tiles.
Originally between the water pipes and the tiles there is a layer of gyprock (drywall, plasterboard) where the waterproofing to be applied on. Now that I bust into the wall, it is lack of solid surface and I wonder what is the best approach to go from here?
One of the easier option came up my mind is to knock out the remainder of the 2 broken tiles without removing the gyprock behind. Apply a soft net over where I can brush waterproof primer and coatings over. After that, apply tiles as normal hoping there are enough ground on its corners for the 2 tiles to sit dry.
Best Answer
At the very least you need to remove the two broken tiles and clean up the edges of the hole so that they are square.
Then, assuming that you don't want to remove any more of the existing wall your best bet would be to stick some batten to the edges of the hole from the back and then you can fix a new piece of waterproof platerboard to that. Seal the gaps and replace the tiles:
The battens don't have to be very big - they don't have to hold that much weight. The faceplate for the shower controls will help keep the new board in place too.
If you can, take the tiles off first and leave a border of plasterboard so that the join between pieces of board doesn't line up with the edges of the tiles. I know this will be difficult, but it will help ensure that the join is water proof.