Cracked glaze/tiles with UFH

[Scott the tiler]

Have a friend who is a top tiler. He put a bathroom floor in with underfloor heating, he also used flexible adhesive & grout. After 6-9 months alot of the tiles have what looks like a tree branch crack effect over them.
It also looks like it is in the glaze & not the tile.
The cracks don't run parallel with the ufh but across it.

Can anyone offer any advise why this has happened?

[merlecollins]

How thick are the tiles?

[Matt]

It sounds like crazing. What tiles were they?

[whitebeam]

Had some tiles years ago and you could here a crackling noise from the glaze

[Matt]

Had some tiles years ago and you could here a crackling noise from the glaze

If I remember correctly it is due to the different expansion rates of the glaze and the biscuit of the tile. The biscuit expands faster and cause the glaze to crack

[diamondtiling]

Had some tiles years ago and you could here a crackling noise from the glaze

Handmade tiles usually make that sound when being fitted.

[whitebeam]

If I remember correctly it is due to the different expansion rates of the glaze and the biscuit of the tile. The biscuit expands faster and cause the glaze to crack

Thats the answer then Matt

[Phil Hobson]

It sounds like crazing. What tiles were they?

Yep crazing, this was one of the reasons sand and cement fixing stopped, and adhesives came in. You see this a lot in old pottery. I wonder if the tiles may not be suitable for ufh. Could be thermal shock?