there is a new product made by HB Fuller under the TEC brand it's called Power Grout, does not change colors, does stain, nor need sealing, I tried to stain it with a marker and it would not stain. in my opinion it is the best grout made to date worth looking into. good luck on your project Here is a link that might be useful: power grout

A couple things I’d like to add. I put epoxy grout in both my bathroom remodels. It can leave a ting of shadow in marble because it soaks in the sides of the tile. You don’t want that area to have sealer on it though so the grout can make connection with the tile. You can barely see the bleed, but it’s there. I personally love it because it adds even more depth to the marble. Here is my slate floor in a light medium gray epoxy grout. It looks almost white in contrast to the black. That’s the trick to the eye. This floor is worn hard. Farmer husbands bathroom with bad shoes. I don’t fuss with this floor except may be once or twice a year, lol. And it’s not hard. I do know that there has been some slight staining near the sink where DH stands to wash up. But it’s slight. The last time I mopped this floor was several months ago. I just sweep it. It could use another mopping I see. The right half never gets walked on, the left is the main walking path into the room. I can see a slight darling. This shower shown below, with porcelain tile, has a narrow grout line. It is a very light epoxy where I combined 2 colors to get a slight off white. No mildew or mold accumulates because it gets wiped down after the showers are done for the day by the last user. Usually it’s just me. I have not washed the walls except 2 times early on 5 years ago, because I thought I should. It is a waste of time because of the daily wipe down with a large microfiber towel. I do spend time with the shower door sweeps from time to time because they will get mildewy. The floor is a cast iron shower pan and I do clean that as typical for cast iron, but because I’m usually the only one using it, that’s not often.

One of my siblings started that profile, I don't keep tabs on them. I started mine roughly 4 yrs ago under a different name. Nice try though. Kelly (cx) gives good info but even he makes mistakes and we've gone behind him to fix them. (We live in the same town) If I'm correct, he does Schluter showers..or is it Kerdi? We don't deal with those products so I'm not sure. He's a nice man and he'll talk your ear off. Last time I saw him, he came in inquiring about what type of adhesive to use for a product. That was years ago. And yes pippabean, I only recommend standard sanded grout for the wet floor of the shower. We mainly deal with traditional mortar beds in the shower, these beds have pan liners in them. The pan liner is there to collect any water that escapes the drain into the mortar bad. A standard sanded grout is needed to allow this moisture to escape properly. Upgraded grouts like epoxy and single component grouts do not allow moisture or gasses to pass through, trapping the moisture in the pan liner. --Now, hindsight is foresight and I should have asked if the OP knew what type of bed was installed. (most homeowners wont know) But then again, I will still only recommend sanded grout. We've been down that road and I sure as heck don't want the OP, or anyone else, to go down that road. That could easily be a $1000+ repair. We've been in business since 1971. We've made mistakes and we've learned from them. My goal on this site is to offer advise and hopefully steer that consumer away from a costly mistake. In the end, it's their choice.

The latest research suggests that sealing marble in a shower creates more issues than it prevents. Your tile professional should be aware of that, and the ongoing experiments. As well as the issues with using epoxy with natural stone. It’s very concerning hat you are posting here instead of working with him for answers to your questions. It suggests that he doesn’t know the answers, and thus is not quified to be doing your job. Further statements just confirm this. You might want to reread the specs on the Red Guard. More is NOT better. You are out of spec. And read the TCNA manual. Not following manufacturer’s installation instructions puts you outside of industry standards. Re vet any tile professional who would do that. Before you let him touch any of the rest. Because starting over now is better than staring o er after an installation failure. https://www.custombuildingproducts.com/TDS/TDS-104.pdf https://www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer