"Grout Once", on another forum some pros have had good luck with it, others have had lousy results. Mostly blotchy colors. Is it the product? The installer? I can't answer that.

I will say that if you're using a basic portland cement based grout you might have good luck with these additives. But if you're using a specialty grout, I'd not want to add 3rd-party additives to a highly formulated specialty grout.

Personally, I don't use any of the additives.

As to sanded versus unsanded, it's pretty much standard to use unsanded grout on grout joints less than 1/8" wide. Sanded for 1/8" wide and over.

"The tile store is telling me I need to use sanded grout on any tile with grout lines over 1/16 or the individual tiles will eventually pop out." Thank goodness they only sell the tile and they don't install it.

Your installer is correct if he has concerns about sanded scratching the marble and glass. There are ways to use sanded with scratchable materials, but the small grout line trumps the issue anyway. Use unsanded.

My opinion about the "Grout Once"? I'd ask your tile installer. If he's up for giving it a try, that's fine. But if you "force" him to use it and you have issues with the grout down the road, it's on you.

Thanks mongoct, very helpful.