Some tile lines require a sealer or a grout release to be used prior to grouting; it creates a barrier so the grout does not penetrate. What are the tiles spec sheet information?

In my experience this has nothing to do with grouting but big changes in temps either in storage or when the tiles were being fired . It is in the finish and the dark grout just made those visible. Were these expensive tile or bargain ones.?

I don't think that is intentional crazing (euphemistically called a "crackle" finish). I think those are just busted glaze and I don't think you can get the grout out of those tiny cracks. I would be very angry at my tile distributor right about now!

If you can't pull them out and redo it, consider a vintage themed bathroom? "I meant to do that."

So i guess crazing may be the wrong word. but these black lines showed after grouting. it was a cheaper floor and decor tile.

I think the tiles are damaged.

ZEP is a great tile/grout cleaner, available everywhere, including Lowe's.

It's definitely crazing. The glaze is cracked. It's done intentionally in some tiles, but this isn't that.

Good crazing:

Poor quality tile and not likely you will be able to remove it. That's a very unfortunate result. What does Floor & Decor have to say about it? It's a supplier issue.

It took three different shops to get a hold of a person. the store assocoate said it was just haze and should clean off and if it didnt i should come in with a photo. i doubt it is haze but pray it can be removed. my installer will try tomorrow to clean it off. im so bummed because my only recourse is to rip out and start over which sucks.

I started the claim process. I have not heard back. I implore others not to buy from Floor & Decor. Terrible and costly experience.