Advice on How To Prepare Sub Floor

[MasterMech]

Hello all,

I am planning on tiling my bathroom floor, I removed the old tiles myself which were very poorly laid to say the least.

Once I got the 4mm plywood they had over boarded with, the floor boards were in a right state so I decided to replace them with new ones.

After doing some research I am a little lost as to how to proceed in terms on preparing the floor before tiling it.

I was going to overboard the floorboards with 12mm plywood & then use tile backer board on top of that as I am installing a heating mat but I see many people recommend using 18mm ply to make the floor even more rigid along with inserting noggins between the joists to make things even more solid.

To throw another spanner in the works I am unsure if I should be using a decoupling membrane like DITRA as I am laying tile on top of a suspended wooden floor.

So I thought I would ask here as I am a little lost on how to proceed.

What does concern me is that if I do need to lay 18mm ply & backer board the floor height is going to be a good 30mm higher which will cause problems for me at the door threshold to the landing.

I have included a few pictures of how the floor looks now.

Many thanks

Adam

[aeromech3]

Hope experts will join, but what size tile are you finishing with, larger tiles need a flatter base? Is the floor stable now and level? Why use ply and Baker board, it is not a wet room ? You will use flexible water proof floor tile adhesive of sufficient depth to allow your trowel not to catch the matt. I would remove the toilet basin and tile under if your plumbing allows but make a cardboard template of where you want the two fixing screws to penetrate to pick up on the joist or good anchor wood. Will the underside of the wash stand stay open?
Example heating matt installation for comments etc.

[MasterMech]

Hope experts will join, but what size tile are you finishing with, larger tiles need a flatter base? Is the floor stable now and level? Why use ply and Baker board, it is not a wet room ? You will use flexible water proof floor tile adhesive of sufficient depth to allow your trowel not to catch the matt. I would remove the toilet basin and tile under if your plumbing allows but make a cardboard template of where you want the two fixing screws to penetrate to pick up on the joist or good anchor wood. Will the underside of the wash stand stay open?
Example heating matt installation for comments etc.

Many thanks for your reply, this size of the tiles will be 600mm x 600mm

I would say the floor is stable now but am unsure on how level it is, but I keep reading that with wood it expands & contracts through the seasons no matter how solid the floor is so they recommend using a decoupling membrane.

No this is not a wet room, ply was recommended but OSB is also viable & this is mainly to cover all the gaps between the floorboards & stiffen the floor up.

Yes the toilet will be removed & tiled underneath, the underneath the wash stand will be enclosed by a plinth.

I want to use the Raychem Quicknet underfloor heating system.

[aeromech3]

I have used marine ply and OSB3 for bathroom floors, though the ply is better to screw into I prefer the OSB3; I used only 9mm, screwed down, for a small bathroom which had a vinyl floor covering over it and has stayed nice for a year now.

[aeromech3]

Guessing you have looked at many videos, they are big tiles so I expect you have suitable cutting tools or you will end up with too many wasted.
https://www.youtube.com/watch?v=DKdFJak1PuY
https://www.youtube.com/watch?v=zX8xupe1Q4A