Thanks for your input Bill. I certainly understand the principles behind sanded versus unsanded grout. I wish I would have fully worked this out before picking up that bag of 3/16" spacers after putting back the 1/8" ones. I just did a test board with sanded grout, and it scratched the heck out of the polished tile surface. I even took some 400 grit sandpaper to it in the hopes that a matte finish might look nice. Not so good either. I've hear Custom Prism mentioned before as a possible solution, but it has a polished marble warning too. I'm really stuck here. I really can't use sanded or it'll look like crap. Unsanded will likely crack and look like crap. Can unsanded be re-applied to fill voids/cracks the day after with any success? Tearing this out really isn't much of a solution at this point. Thanks for any input.

Less than 1/8" unsanded. 1/8" and over, sanded. What most installers object to is they claim the sand will scratch the face of polished stone. Now, I've heard this from enough installers and contractors to believe there might be some creedence to this, but my own experience is no way. I used to work on a commercial crew that went up and down the east coast doing the tile in Lord and Taylor, and Filenes. In both stores, we used crema marfil marble for all the aisles. We installed all of it with a 3/16" grout joint, which meant using sanded grout, and when it came time to clean off the excess, no sponges were used. It was a buffing machine with a burlap bag and dry grout that was used to buff tile tiles clean. Even with the machine and abrasive burlap, there were still no scratch marks.

but I do know that sanded is much stronger and hold up better. I think it is intended for 1/8" or wider grout lines. It's not that it's stronger. It's that it doesn't shrink as much, because of the fact that most of its bulk is the sand. As for the explanation of the different grouts, I just posted this in an FAQ thread on the gallery side of the bathrooms forum. Here it is, copied and pasted: Although there are others, for all intents and purposes, there are two kinds of grout-- portland cement based, and epoxy. The portland cement based grouts are the conventional grouts that have been around for millenniums. Although in the last few decades, they've been modified with latex and other polymers to make them stronger and more resistant to mold and mildew, they're basically the very same grouts that have been used since Greek and Roman days. There are two kinds of portland cement based grouts. One is sanded, and the other unsanded. The only difference between the two is, as their names imply, the sand. The ONLY thing that determines which grout should be used is the joint size. NOT the glaze, NOT aesthetics, NOT the material (ceramic vs. glass or polished marble), NONE of those. I'll repeat-- the ONLY thing that determines which is used, is the joint size. Anything under an 1/8" takes unsanded grout. Anything 1/8" or bigger, you use sanded grout. If you use unsanded grout in larger joints, the cement in the grout will shrink way too much as the water evaporates out of it, and the joints will end up shrinking and cracking bigtime. If you try using sanded grout in smaller joints, the grains of sand will literally clog the top of the joint, and not allow the grout to get down INTO the joint, and the grout will flake off in a matter of days. As for the Epoxy, most epoxy grouts use a much finer "sand", and therefore can be used in any size grout joint. Further, epoxy grouts are everything people say they are. They're much easier to clean, practically stainproof, and also extremely expensive. Most epoxies will cost atleast 4 times the cost of conventional grouts, and the installer will also usually charge a premium of between 1.50- 2.50 a foot for the use of epoxy grout. There are alot of people who will disagree with me, but my own opinion is that for most residential installations, epoxy grout is bigtime overkill. The ONLY times I'll recommend epoxy grout is first, if you're installing a tile countertop, and two, if you have animals in the house that either aren't housebroken, or are prone to accidents. In either of those cases, epoxy might be worth the money. For anything else, though, conventional grout is more than good enough.

I understand your angst, but color inconsistencies are really a non issue. Over 32 years I have installed many tile applications and have never had a client find an issue with grout color variation. More important is the sanded/non sanded. 1/16 really needs a smooth grout unsanded, and you should avoid certain grouts that are "hybrids" - grout for thin joints that has fine particle filler. You can never get them to have even suspension through out the mixture.