outdoor tile

I have reddish colored 6by6 tiles on front patio.There are lines showing up in a lot of these tiles.Its looks like limestone (white powdery lines)Tiles do not seem cracked but most lines are in same direction.Any suggestions on fixing this ?Thanks

 

Dear Conal:

And, if it's not to much to ask, what kind of tiles are you talking about?...

Are they manmade or are they natural stone?

You mention something about limestone, but it doesn't seem like you're saying that your tiles are in fact limestone…

No matter what, I'm afraid that no matter what your tiles are mode of, they're not appropriate for outdoor installations.

Ciao and good luck,

Maurizio Bertoli