Advice on porcelain cracked tiles please - Tile Advice

[Tone2222]

Had wet system UFH installed on a concrete subfloor to the whole ground floor ie living room, kitchen and hallway (40 sqm). UFH Panels were laid down that contain grooves for the UFH pipes to sit in. The plumber used an adhesive to fix down. It was then latexed over using around 3 mm thickness latex which just covered the pipes. Bonding agent then applied to latex. Was then tiled over with flexible adhesive and grout. Waited 2 weeks before turning on UFH which we did slowly and increments of 5 deg. A day after turning on a crack appeared in 1 corner tile. The next day after turning on and at 15 degrees, hairline cracks appeared in 4 other corner tiles and these literally cracked over night. All the corner tiles are corner cuts around kitchen units and corner cuts around door ways. The cracks reach the grout lines but the grout is intact and does not cross over to the next tile. Tapping on these cracked tiles reveals many hollow points. Tapping on tiles elsewhere that are not cracked reveals that some of these have hollow points. Most of the tiled area sounds solid. I’ve been assured they have not been dot and dabbed by the tiler. The tiler used grout between the tile and the kitchen units. The plumber blames the tiler as if there is movement from the UFH then the cracks would be more extensive and not just limited to the corner tiles. Spoke with the tile shop and they said the tiles are suitable for UFH.

Any ideas on cause?Any ideas on solution? If we replace the cracked tiles surely they will crack again? Do I need to have the whole thing lifted and redone as if this has happened after 2 days of heating my heart sinks what will happen in the coming weeks and months!

And no anti fracture membrane applied btw.

 

[Dave]

Morning.

I personally would have used a crack matting.
Back to your project. First off what is the recommended thickness of SLC by the ufh manufacturer? . 3mm imho doesn’t seem enough and what SLC was used ? .
The cuts to the kitchen units/ doorframes etc , should be siliconed to allow expansion/contraction. And finally, what adhesive was used ?

 

[Tone2222]

Many thanks for your thoughts. The standard setaflex S1 flexible adhesive was used. The UFH manufacturer was contacted and in agreement with the Latex thickness. Even their instruction manual advised 3-5 mm. The latex used was NX floor leveller. I should also add the heating was turned on on the lowest setting and increased in increments. It only took a few days for the tiles to crack of their own accord.