Any idea why my tiles are cracking?

[Biscuitsplease]

Good morning

We've had a gradually cracking tile in our kitchen. We moved in late 2019 and noticed it about 6 months later, it's been getting gradually more cracked. There's also another hairline crack on a nearby tile and some cracked mortar

We'll need to replace it at some point, but I'd hate to do this and the crack re-emerge. Also slightly worried about potential movement? Thankfully no cracks elsewhere

 

[Biscuitsplease]

Not cracked mortar, cracked grout

 

[jacko555]

What are they on?

Is the underfloor concrete or wood?

 

[Biscuitsplease]

It's underfloor concrete

 

[foxhole]

Probably laid incorrectly with small voids, air bubbles in cement .

 

[freddiemercurystwin]

Respectfully, how do you know it's a concrete floor?