Laying slate on 2 floor types in one room

[zambian]

Hi, I have to lay slate tiles in a kitchen. half the room is concrete floor and half wood. Slate should be fine over both (if the wood is 18ml ply) so I've been told, but what about the join between the concrete and wood? If both are the exact same height do i need hardy backer or something else (some sort of matting?) to ensure there'll be no movement or cracking when the tiles are down? Thanks.