BAL BAL or Mapei - Decoupling membrane/anti-frac?

[True North]

I did, thanks for clarifying!
It's an old victorian floor so ideally without a visible joint, if this is what is meant: When To Add Expansion Joints To Tiled Floors - https://www.tilefixdirect.com/blog/2015/06/when-to-add-expansion-joints-to-tiled-floors/

Am I wrong to even think an anti-crack membrane would suffice?

Cheers
TN

 

[True North]

noting fishy at all, apologies.

 

[Andy Rhodes]

Screwed an descent cement board on top of your timber floor & stick the same board down over the cement floor with a good tile adhesive using the board edges to form you movement the span a movement trim over that joint for good measure