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.

 

[Badger40]

Thanks for the reply!

The existing that cracked was tiles on 30mm foam boards on 3mm ply. They did add extra noggins but there is no cement board in site. Does the above sound like it was the problem?

 

[Badger40]

Attached photo

 

[Badger40]

Can’t really see how the fall was achieved to be honest but there wasn’t much fall at all.

I take it undercut or remove tile and cut down after tray is in are my only options.

 

[Madrab]

The existing that cracked was tiles on 30mm foam boards on 3mm ply

Looking at the pics that may actually be some type of former but most of then are made from SMC/GRP materials.

Older ones used to have a High density polystyrene type core material but they would normally have needed to be very well supported below.

Yeah, I'd have all that up back to the joists and reset the floor before the tray goes anywhere near it. Only way to be sure.

 

[Badger40]

Yeh this stuff is just like thick jackoboard insulation with the middle being a bit firmer. Even at 30mm I guess it’s not great to tile straight onto if it’s on the floor. I was quite surprised to push a screwdriver straight through it into the joists below.

How does the plan below sound.

Rip it all out
Install cement board floor
Work out the undercut need leaving room for a bead of silicone
Undercut tiles
Tank or use a strip on the wet edges against wall, install shower tray on sand and cement as per manuf instructions (mira flight shallow)
Silicone and test

 

[Madrab]

Sounds like a plan.

As suggested, just ensure the cementitious board is thick enough to load bear properly.

Sand and cement can be difficult to get the consistency right - if anything like that I'd use a flexible tile adhesive - A good quality flexible tile adhesive tends to be more workable and more suited to the application IME.

 

[Badger40]

Thanks!

Never used a tanking edging strip before I take it all I can do with that is attach it to the tray and trim it to the height of the undercut?

 

[Madrab]

Never used a tanking edging strip before I take it all I can do with that is attach it to the tray and trim it to the height of the undercut?

Nope - if you get it as part of the tanking kit then you use a primer on the wall and floor, then paint in a coating of the tanking membrane and whilst that's wet, stick the edging tape onto it spanning the floor up to the bottom of the tile undercut, then paint over it again with the membrane, a good couple of coats - make sure the corner is nice and sharp so the tray will sit in nice and square to the wall and let it all dry, that'll create the reinforced waterproof wall to floor edge. Then just before the tray's to go in, a good fillet of silicone on the bottom edge and wall and then push the tray in nice and tight and square and clear off the extra - silicone should be squeezed out all the way along the join, that way you know there's enough in there.

That should give you a watertight seal all the way along.