Floor prep advice, nasty springy chipboard patchwork

[Bathfix Bob]

I've just started a new bathroom today (floor to be tiled), ripped everything out and when I pulled back the lino my eyes were furnished with a dodgy looking chipboard floor.

The basin had been dripping so a 20 inch patch was rotten. Under the shower tray (no bath) the floor is a loose squeeky patchwork and the same again on the other side but not quite as bad. There's not a square ft that isn't squeeky or springy.

The ensuite is smallish about 7 ft square.

I've recently had a movement issue with another bathroom so I've learnt the hard way and I'm dammed if I'm going to make the same mistake twice. This time I've allowed myself more time to prep the floor and I want a solid job I don't have to worry about when I've gone.

Whats the best way to prep this floor? What would you guys do?

[Bri]

Strip it back to the joists, extra noggins, 18mm minimum ply, then cement board glued and screwed. Also check the joists aren't rotten when you can see them, if there has been a leak you never know.

[Bathfix Bob]

Thanks for that, I've always shyed away from 6mm cement boards because of the extra cost but I'll use them from now on.

What glue is used to stick them down?

[Sir Ramic]

Hardibacker use single part flexible adhesive.
No More Ply use Megastrength polyurethene adhesive....Both with screws although Hardibacker say ring shank nails but I dont like that idea myself.

[Bri]

Just use flexible tile adhesive, put it on with a 4/6mm trowel.

[Bathfix Bob]

Thats great thanks, one more question though regarding the shower tray.

I have 18mm ply on the joists now and I'm ready for the Hardiebacker soon, does it go under the shower tray or do I just seat the tray on the ply and then hardie up to it?

I would have thought underneath.

Yes this is the first time I've done a floor with cement boards.

[Bathfix Bob]

So does the Hardibacker go under the shower tray guys?

eg do I seat the tray on the cement boards?

[Daz]

I would mount the shower tray on the ply. Please note, the ply floor needs to be completely stable prior to installing the cement boards, as the cement boards do not add any strength they just ensure a tileable substrate.

[Scott]

Id sit the tray on the ply and cement board up to it, this way you have less of a step into the tray.

[Bathfix Bob]

Thats great thanks, its a quadrant tray though so I think I'll have to draw round the Haribaccker first.

Don't worry the floor is stable, boy is it stable. Nogins everywhere.