Tiling kitchen floor - half boards, half concrete?

[Skaffen]

We need to get the floor of our kitchen tiled - at present half of the floor is concrete (where the kitchen has been extended) and the other half is boarded (floorboards, not ply).

The two surfaces aren't at the same level (probably a 3-4mm step from concrete to boards at one corner).

We've had two tilers come round to give us quotes, both of whom were recommended by our local tile shop and whose quotes were within a tenner of each other.

First one didn't seem phased about the floor and said he'd use some new product in the adhesive (?) with the only caveat being that the boards would need to be screwed down rather than nailed?

Second one looked horrified at floor and said the whole thing would need to be boarded with 12mm ply before tiling (which we'd need to do ourselves). He said the best solution would have been to remove the floor boards and replace with ply, but as we've already had a new kitchen installed, this isn't practical.

The kitchen fitter installed everything 20mm higher than usual to compensate for ply + tiles, but he mentioned 9mm ply, not 12/18mm, so I'm starting to worry that we may not have enough height under worktops for our appliances if we go with 12mm ply?

What's the best solution? Do we need to board the whole thing over and will that give us a level floor?

Thanks.

 

[gcol]

You definitely want to board over the floorboards with WBP ply. 9mm will be fine if the floorboards are sound and not springy. Screw the ply down every 6-8" all over the sheet surface.
I've never had this problem of wood/concrete floor but I would think you'd be as well using a self levelling compound to bring the concrete section up to the same level as the newly boarded section.
Then proceed with tiling, you'll need to use a flexible adhesive like BAL Rapidset Flexible Adhesive for the wooden section. You could use the same adhesive on the concrete but the flexible stuff is quite expensive, so you might want to use an ordinary floor adhesive for that section. Then grout with a decent flexible grout - use the same grout for both sections.