Replacing tiled shower floor with shower tray

[Badger40]

Hello first post here.

Bought a house with a shower that has a tiled floor, tiles are about 25mm square, after using for a couple of months we started to get leaks downstairs, found the plasterboard was bowed so had been happening for a while, ripped the lot down so it can be replaced. I’m the shower found some cracks in the grout so regrouted but it leaked again. So we have no confidence in the shower floor, and want to put a tray in before repairing the down stairs ceiling.

So started pulling up tiles, found water marks under them in a few places. Tiles was laid on insulated tile backer board about 35mm thick and 3mm ish ply straight on the joints with some extra noggins. Does that sound like a good design or does that explain the cracking and leaks?

For the new shower tray install. I take it the way to do it is undercut the wall tiles and slide the new tray into the undercut? What is best under the tray ply? If so what sort of size?

Thanks for any help.

 

[Badger40]

Just bumping to top. Thanks

 

[Madrab]

If the tile backer board is cementitious and at least 12mm thick, minus insulation, then that should be strong enough, to minimise deflection. if that was straight down onto the ply though then there would probably be movement in the insulation when weight was applied

2 primary reasons why the tile grout/adhesive would shift, wrong adhesive/grout or floor is deflecting causing movement. Ideally there would be a decoupling layer under that too, which can absorb some of that movement.

TBH if the floor has been compromised and water got through to it, I'd be starting again. That way it is known what's there and that it will be up to the job. How was the 'fall to drain' in the tiles created?

For the new shower tray install. I take it the way to do it is undercut the wall tiles and slide the new tray into the undercut? What is best under the tray ply? If so what sort of size?

Hmmm - a tile undercut may work but you have no way of guaranteeing a waterproof seal all the way around the wet area edges unless the wall in there is in really good condition and smooth and you could add in a tanking edging strip and waterproof that space. Floor would be WBP/Marine ply/OSB3 board @ a min of 18mm and well supported or a cementitious board equivalent with the tanking edging strip and a wide membrane coating all around the edges with the wall.