This is white Italian Marble and it received 3 coats of sealer. Look at the water bead. A solvent based sealer has smaller particles than water based sealers and will seal deeper into the stone. Aqua Mix is my preferred sealer of choice. Always test your sealer and inspect the results before jumping in feet first. Some of my biggest tilling mishaps have resulted in learning proper installing techniques and proper dwelling times. Much better to go slow and steady and do the job in 4-5 coats than 1-2 heavy ones. Keep a bunch of lint free rags with you and read up on this procedure from multiple sources before starting. We have made it a rule since last summers "Enrich n Seal" disaster that a test board be made for every job and that the grout and sealers all installed prior to setting tile. This test board can aid in tile layout and allows the client to see the grout installed and dried and what the sealer looks like finished. I think marble in a bathroom is timeless but it comes with caution. Iron content and other strange "Tile Fairy" issues come up and there is always a chance you may need to replace some or all of a natural marble installation. If you don't like these risks, do extra testing, buy better tile from a better supplier or switch to porcelain. Here is a link that might be useful: Aqua Mix - Ultra Solv

Wow, this also happened to me. It was my bathroom floor which was mercifully small. Fortunately (or maybe not) it was my brother-in-law's work, a great guy who was just helping me out. :( He finished the job and left for home, on the other side of Calif. I was just cleaning up and noticed chunks of grout would pop out and/or turn back to sand. The tile store said it was because my grout was old and it would have to come out and be regrouted. As I was on hands and knees removing grout, entire tiles began to lift off. So, not just the grout was bad, but he had screwed up simply laying the tile. It was a total Charlie Foxtrot. At the time I was undone by this, the last in a series of well-intentioned blunders that made my poor bathroom a disaster. I paid a guy to redo the entire floor with new tile. The bathroom and I recovered. Hopefully you and your floor will too.

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've only used the pre-mixed grout a few times, not a big fan. The instructions for cement grout warn about color variation but, in 20+ years of installing tile, I never had an issue. You can get color variation if you add more water to the grout after it's started to set up. The bigger concern there is that it will weaken the grout. Another cause of color variation is using different bags. If the job calls for more than one bag of grout, you're supposed to "box" them (mix them together). A kitchen backsplash is unlikely to need more than one bag (probably only a quarter of a bag.) My advice would be to use un-sanded cement grout. For 1/16th joints, add water and mix it until it's about the consistency of peanut butter or just a bit wetter. Let it set for about 5 minutes to "slake" then mix it up again. As for the brand: PolyBlend by Custom, Laticrete, and SGM are a few I've had good luck with. I've heard but never saw first-hand that Mapei had color variation issues. If you have to use the pre-mixed stuff, it won't scratch your marble. Pre-mixed grout typically contains sand (silica) which won't scratch the marble but will be difficult to get into 1/16th joints so you will probably end up with several unsightly holes in the grout that will need to be touched up.