Ply thickness for tiling

[pertinky]

Hey guys,

I'm taking up all the 22mm floorboards from the bathroom and wondering what to replace them with.

The joists span 2.5m, and are at 420mm centers (120yr old house).

I'm planning on overboarding with 6mm No more ply.

The hallway (which will lead in to the bathroom) has french oak boards down which are currently the same height as the floorboards so any increase in height needs to be kept to a minimum.

 

[foxhole]

No more ply is used on top of boards to improve strength not instead of boards.

 

[pertinky]

@foxhole I think you misunderstood. The floorboards are fecked, so being wholey replaced but im not sure whether I should use 18mm or 22mm. I'll be putting 6mm NMP or hardiebacker down to tile on.

There are no literally horizontal supports, and some pretty hefty notches near the end of the spans so I'll be spending tomorrow strengthening it all with some sisters joists and some noggins

 

[JohnD]

even 18mm ply flexes a little. Enough to need nogs under all long edges (with all short edges on joists.).

you only feel it when standing barefoot on the joins, but I think it would be enough to crack grout.

 

[pertinky]

even 18mm ply flexes a little. Enough to need nogs under all long edges (with all short edges on joists.).

you only feel it when standing barefoot on the joins, but I think it would be enough to crack grout.

Would the cement board not counteract this?

The main issue is going to "large" step from hallway

22mm (current level) + 6mm cement board + 5mm adhesive + 10mm tile = 21mm raise

 

[JohnD]

it should, but although I've put down new floors, I haven't tiled them, so I don't know. I can feel the flex though.

 

[foxhole]

22mm ply would be enough without anything on top.

 

[Lower]

If you put down 22mm ply you won't need the hardibacker.

Put noggins on the joints and you have a very solid base to tile on.

 

[pertinky]

@Lower I try to avoid tiling on ply to be honest!

22mm ply would provide a very stable surface (i've got a 1200mm x 800mm stone resin shower tray to go down and its quite heavy)

I've had to sister the joists at the end of the spans, as well as noggins every 600mm and extra around where the bath/shower tray will sit.

The first fix is woeful though pipes and T&E all over the shop!

 

[pertinky]

@foxhole seems sourcing 22mm ply is going to be an issue as well!

 

[foxhole]

Maybe 24mm ply?
https://www.simeonbateman.co.uk/index.php/sheet-material/76-ply-wood-birch

 

[pertinky]

I've gone 25mm in the end @foxhole.

Even with 18mm + backer I'd have been at 24mm. The show tray is pretty hefty so probably for the best it'll be absolutely solid surface although the additional weight does concern me a little!

 

[pertinky]

So I went back on myself, and returned the 25mm in favor of 18mm. Too much of a step up from landing. Going to do my best to limit deflection in the floor, and get some super flexible adhesive.

Not ideal, but that will mean the finished floor is approx 10mm above the floorboard on the landing which I can live with.

Thanks for the help guys!