Setting Out Who Does The Levelling??

[JB131]

Thanks all for your feedback, opinions and ideas. I have an experienced tiler who is willing to take it on. His approach is not dissimilar towhat you have outlined Lee Mac. Generally was just quite surprised by the split of opinion that I was getting. I would say roughly half of those that looked agreed with LocalTiler's view. As a parting shot, when there is such a difference of opinion as a customer I lose confidence generally. But I guess people call it as they see it based on their past experiences.

Thanks again

 

[hmtiling]

Marmox overlay would be better than ply imo.
Just to mix it up again

 

[hmtiling]

Glued with SPF and screws and washers.

 

[SJPurdy]

A few points to consider:
The 3mm ply needs taking up and the flooring under it inspecting - is there ventilation underneath, are the floor boards in good order and firmly fixed to a rigid joist system?
The quarry tiles on ash floor I assume to be a compressed ash bed with quarry tiles laid on top of it and fixed using gravity, something that I've tiled on a few times before (small areas) and had no callbacks/problems ( but then I have been very lucky).
Is there any damp proof membrane or insulation under any of the solid floors?
Even if the timber area is repaired/prepped properly and the solid floors are levelled up to it and then the whole floor is over-boarded with backer board, insulated backer board or wood sheets!! then there should still be a movement joint in the tiling above the wood-solid interface.

Have you considered taking out the whole miss-match of floors and replacing with a new properly damp-proofed and insulated floor slab?