Concrete to Ply Bathroom Floor

[2020Tiling]

Got a 4 mtr Bathroom floor with half being concrete and half chip board over layed with ply to make it flush with the existing concrete, it is at the minute level ish, and was seeking advise for the best way to over lay over the 2 substrates, Tiles going down are 600 Ceramic. Is it acceptable to over board the whole floor with 6mm cement board ? There's no UFH going down. Or is there another way you guys would tackle this? :smilewinkgrin:

 

[Peter]

What way is the floor setting out with a full tile off the join?

If I have to straddle, I'd Ditra the tile over the join and rubber crumb. Not textbook but better than splitting and fitting an expansion joint if it is in the middle of a floor. For the sake of 4 metres though I would just Ditra the whole thing.