[rony]

Hello, I have a home in France built in 1907 and am planing on tiling a second flevel floor. House built of stone. Floor joists are 3 inches wide by 8 inches deep , 16 inch centers.
The planks overtop are two by fours. Flat, but some are cracked and some have been made narrowers to fill spaces.
Should I lay 3/4 inch plywood over the planks or should I remove them.
Keeping in mind that some of them go under the walls of adjoining rooms.
I have 5.5 cm of height to reach where the old terre cuit and old cement layer were.
Thank you

 

[rony]

Correction: The planks are not two by fours. The are 3/4 inch think and 3 inches wide.
We had to lift the planks to clean underneath, as when we removed the old (cement?) dusty layer under the old tiles lots fell between the planks. Thanks for helping.

 

[Bondo]

I have 5.5 cm of height to reach where the old terre cuit and old cement layer were.

Ayuh,... That's just over 2",....

How thick are the tiles,..??

Maybe a double layer of plywood, 'n 1/2" durrock,...