Horsehockey. What happens is that moisture from the grout will seep into the stone.... INITIALLY. Within 48- 72 hours, it'll be gone.

Additionally, if he uses any of the sealers I've been recommending, they wouldn't stop the stone from discoloring, anyway, being that they're "breatheable!

Thanks so much Bill! I must say it sounded kind of odd to me. Would you recommend sealing the top of the tile when the project is complete?

They can if they wish.

But not necessary?

Let me put it this way. I've heard some real horror stories in here from people who haven't sealed their marble. But I also had a marble master bath for years. It never got sealed, and was none the worse for wear.

Especially being that this is a powder room, it's not going to see as much use as a normal bathroom would, especially with respect to chemicals, such as make up, soaps, dyes, perfumes, etc.. Personally, I wouldn't worry about it.

I presealed 250 sqft of limestone before installation. I was careful not to get the sealer on the sides where the grout would go. I didn't want the sealer to affect the grouting process. I'm glad I presealed because the coverage was much better than sealing afterwards.
Donna

Thanks alot guys. As always, your advice is invaluable!
Sharon