level wooden floor under backer - Tile Advice

[Neverendingdoerupper]

Hi all,
I'm a new member and have been searching the forum for a solution to my latest issue but thought best to ask. Got loads of good advice from the forum to help finish my wall tiles, thanks.
Anyway, please see pic

I'm tiling our 1st floor wooden floorboard bathroom floor and have planned to use 6mm hardiebacker on adhesive and screws then tile, now I'm onto this job I've noticed a bit more that the floor falls away where some boards have been cut leaving a row of short boards. It's quite flat than falls between 6-9mm from 50cm to the bath. It's an old Victorian terrace that's had some movement over time. It's all sturdy with no creaks or bounce but I'm wondering how to level this bit out, before backboard or after?
Take a bit out with adhesive under board and the rest whilst laying? What would you guys suggest?
Also do I need ditra matting as I've heard it mentioned with floorboards?
I'll try and post a pic.
Thanks in advance for any help,
Matt

 

[macten]

I'd personally lay the backerboard and then float some rapid set in with a straight edge if it's just that little bit.

 

[Neverendingdoerupper]

Thanks macten, I'm using standard set bagged adh for the tiles as I'm taking my time, but I do have rapid set. Should I let the rapid set go off and prime before tiling with the other adhesive?

And I shouldn't need an uncoupling mat? Are they for UFH or something?
Many thanks again

 

[GoneGuy]

Uncoupling mats are generally used for lateral movement as with wooden floorboards you would be dealing with deflection so hardiebacker board glued and screwed would be fine.

 

[Time's Ran Out]

What type of tile are you fixing?

 

[Flintstone]

You could double board that area

 

[Neverendingdoerupper]

Thanks, I'm laying 600/300 ceramic 10 or 11mm floor tiles.
I thought about putting a strip of board down there first but worried the edge of it and the 0-6mm slope between the flat floor and packer board might cause a stress area on the board above?
If I use rapid set on top what are your thoughts on priming it before I tile with standard set?
Cheers

 

[macten]

You don't need to prime the rapid set but, although not necessary, I tend to prime cement boards.

 

[macten]

?

 

[Simon Dale]

?

@pdc means prime prime and prime. If we ever float adhesive in, the day after we prime.

 

[Dumbo]

I prime everything .

 

[GAZ5518]

Board it .. Prime it ... Make up the deficit with your adhesive.. ( doesn't look too bad from your picture)
Good luck