Advice on herringbone pattern across old kitchen timber floor and new concrete extension floor

[KarlFin]

Hi,
We have a kitchen extension currently under way, the kitchen floor is timber and extension is concrete. Total area 50sqm
We hoped to place a herringbone pattern in wood effect tiles - size- 15x90. 6mm thick.
We are aware of the need for an expansion joint between the two substrates to help prevent cracking/tiles lifting, however we have been advised to avoid herringbone due to the possibility of the timber floor not being level which could throw the square off and cause issues in the middle?
are there any concerns with what has been said or would anyone have concerns with the projected plan? Could we level the timber floor and how would this be done?
Thanks

 

[Huddersfield Tiling]

This is a seriously bad floor to try and tile as a whole.
There are major issues with the gap between the 2 floors and it's not a small gap. Moreover, the difference in levels look hugely out of level.
I can't really see a solution on this one because of the vast difference in levels and the massive void between the floors. Some floors of this kind can be dealt with, but unfortunately, I would condemn this floor as unsuitable to tile as a whole floor. Think about 2 separate floors with a ramp, not using tiles.

 

[KarlFin]

Apologies I should have mentioned the cement floor hasn’t been finished yet to level with the timber!

 

[Huddersfield Tiling]

Apologies I should have mentioned the cement floor hasn’t been finished yet to level with the timber!

Okay.
If you can get both the floors almost level with each other (+/- 3mm), then you could use an uncoupling mat over the entire floor before tiling. I'd be thinking of quite a thick one, such as Durabase. Both floors would have to be sound (boarded over possibly with Hardibacker or other beforehand), rigid, primed and good to accept a strong bond of an uncoupling mat. The gap between the 2 floors would have to be massively worked with using every possible kind of reinforcement beforehand, and this is the major issue regarding movement. An uncoupling mat will take some lateral movement, but not more than a few mm.
Once the mat was laid, I'd advise using a fibre re-enforced levelling compound over the entire floors. Wait a week or 2, and then check for cracks in the compound. No cracks, go ahead and tile using a a high-spec flexible adhesive (CT C35 F6).

 

[Danielle]

Apologies I should have mentioned the cement floor hasn’t been finished yet to level with the timber!

Hi Karl,

Did you end up going ahead with the herringbone time? If yes did it work or crack?

We have the same issue.