Water UFH Advice Required Before Tiling,again! - Tile Advice

[dogbower]

Hi
We have a kitchen/diner with wet underfloor heating, its a n L shaped room 8M long by 6m at its widest, narrowing down to 4M.
We installed the underfloor heating ourselves, in a 70mm sand and cement screed, around 7 years ago. I then tiled the screed with large format slate tiles. After a couple of years the tiles showed signs of movement in some of the grout lines, and gradually some tiles have come loose.
I have now lifted all the tiles to sort this out and found, a couple of cracks in the slab, and poor adhesion between adhesive and tiles.
This appears to be because, I didn't put an expansion strip through the slab? The UFH has 2 circuits in this room.
I also have areas of the room that are not heated, under cabinets etc, but they are tiled
The screen was fully dry before tiling, underfloor heating off when tiling and gradually back on after.

I now want to sort this out and would like some advice.

I am planning to-
Prime the screed, self level in a couple of areas, fit decoupler membrane throughout the room, tile.
I am planning to use Webber Spf rapid set adhesive.
Do you think this should sort my movement issues?
Any other suggestions? Do I need to look at an expansion strip as well?

Thanks Stuart.

 

[hmtiling]

Does the screed have expansion joints in it? If not,I would say the decoupler will suffice on that area. If using a large format tile or stone back butter the tiles too. I'd prime the slc but some don't.

 

[Tile seller]

Sounds like you have a good plan tbh.
I was thinking it's touch and go across the 8 meter length considering it's UFH. Should be ok but, if you don't mind using an expansion strip then why not.
Make sure the backs of the tiles are clean and dry before you tile to ensure you get a good bond with the adhesive. I know your reusing your old slate but from new they can be a bit dusty on the backs some times.

 

[hmtiling]

Reusing the slate? Wow, the adhesive really didn't bond first time

 

[Old Mod]

Reusing the slate

I can't see that written either Harry.

 

[Time's Ran Out]

No mention in post of reusing old slate!
You don't say how big the cracks are or if they are at an expansion line in the screed.
On all UFH I'd use a decoupling membrane.
8 metres is outside the recommended measurement for not inserting an expansion joint and it should go through the membrane and tile.

 

[J Sid]

Make sure you have a clean adhesive free expansion joint around the perimeter of the room

 

[Tile seller]

Apologies, Ref: reusing old slate tiles. I somehow just seemed to imagine it.
Who knows what tiles he is using, I certainly dont

 

[dogbower]

Apologies, Ref: reusing old slate tiles. I somehow just seemed to imagine it.
Who knows what tiles he is using, I certainly dont

Yes amazingly using the old tiles, carefully removed and cleaned, but no they didn't stick very well.

Crack not through expansion in slab as I didn't put one in, oops.

So do as I first suggested but also stick an expansion strip in then?

Thanks for the replies,

Stuart.