Tilling over an existing tilled floor surface - Adhesive advice required

[mark1111]

Hi.

I'm looking to tile over my kitchen floor with slate tiles. At the moment, the kitchen floor has a solid concrete base and is tilled with either porcelain or ceramic tiles (I have no idea which but it's likely to be the cheapest available the previous owner could get hold of). The floor is solid without any movement.
Normally I would have removed this layer of tiles but it just so happens that when I knocked a wall out at the end of the kitchen, the height of the tilled surface matches the height of the concrete floor we revealed.
I'm aware that I will need to scuff the shiny surface of the tiles that are already down and may even need to cut grooves into them but what sort of adhesive do I require??
Two shops have told me that I need flexible adhesive but I can't understand why when the floor is nice and solid. Can anyone advise me?? If I decide to go for a ceramic tile instead of the slate, will this make any difference to the type of adhesive I need?

Many Thanks,

Mark

 

[Gall.B]

Hi, How do you know the floor is 100% sound mate and how big an area is it?

Would still want to lift them tbh to be sure & level of the slc.

How thick is the Slate you are using surely wouldnt be far away by the time you slc and lay the tile with a good bed?

Prep is perhaps the most important part of any job.

 

[DHTiling]

Top advice above... deffo rip out and re-do

 

[DHTiling]

Oh! and welcome.

 

[Michael kiss]

:welcome:

 

[mark1111]

Thanks for the help so far guys.

The total floor surface equates to 30m2. Approximately 4m2 of that is uncovered at the moment (bare concrete) and it’s that area of the floor which sits higher than the rest, or at least would if I removed the old tiles.

The remaining 26m2 has the old tiles in place. I'm a bit reluctant to remove all the old tiles and then have to either use some self leveling concrete to bring it up to the height of the bare concrete floor or use extra adhesive (I presume those would be the two options??).

I presume that the existing floor is solid because none of the tiles sound hollow when knocked and despite by best efforts, I can't get any of them to move. All the old grout is still in place which may suggest that the tiles haven't moved. I estimate that the tiles were put down in 2003. The house was built in the 1930's. Overall, the floor is pretty level.

The slate tiles I'm looking at are between 10-12mm in depth.


Going back to the original question, let's presume the floor is solid and I opt for the tiling over the existing tiles option. Would flexible adhesive be required or would normal adhesive do the job? Is there a particular brand you would recommend in these circumstances?? What would the risks of doing this be rather than stripping back to bare concrete?

Thanks again for all your help.

Mark