Hi, I tiled my bathroom 3yrs ago and where there are stud walls I used wbp ply to line the walls then sealed with a Pva bond and tiled on to it. My shower cubicle falls in the corner of the two stud walls and up until now has been fine. The other day I noticed the grout on one of the tiles at the bottom was falling out so I took the cubicle off and pulled away the tile. It seems that water has been seeping in around the 3mm silicon bead along the bottom and over time being absorbed into the ply (see photo). I was going to dry this out. Re bond / re tile and re seal .I'm not sure if there's any waterproof paint I could apply first or should I use a plastic seal where the tiles meet the shower tray as id rather this not happen again. I could pull off the ply and use aqua board but I feel it would be a massive job as its tiled floor to ceiling all round so id be pulling away a lot of tiles to get to the joints in the sheets and I'm not sure if the ply is 12mm or 9mm I know aqua board is 12.5 mm at wickes. Any one have any suggestions / ideas. Thanks