oh geez, that is ugly. Total installer error. A sealer of does help reduce the chance of grout building up in the cracks and crevices of natural stone, but by no means does it eliminate it. The use of a small brush, even something as simple as a toothbrush, during grout cleanup would have eliminated your problem. The solutions have been covered by Bill. Due to the thickness of grout that needs to be removed, this needs to be a combination of chemical (acid) and mechanical, with the mechanical "assisting" the acid. In overly simplistic terms, the acid will dissolve the binder in the grout, leaving you with the sand filler, that will simply fall away. Mechanical abrasion (a stiff brush to start with) will assist the acid in dissolving the grout and cleaning the tough stuff out of the micro-grooves and pores. If they show up with a jug of muriatic acid, send them home. If they say "what's sulfamic acid" send them home. The discoloration on the grout after their premature cleaning attempt? That's why the instructions say to not use it on green (uncured) grout. There's usually a 10-14 day waiting period. Cleaners can get into the uncured grout and "burn" the grout, resulting in an unremoveable powdery-looking residue on the grout surface. You have so much buildup on the stone that I would not let them do a "mop" type of application, sloshing it everywhere. They need to apply it to just the built-up parts, because it's going to take several applications to get through the full thickness of some of those build-ups. If you have them proceed with the cleanup, find out what product they intend to use, then read up on that product before they show up to use it. Oh, and one of the beauties of sulfamic versus muriatic is that they could use muriatic that's so strong they could do more damage than good. With sulfamic, you mix crystals into cool water. Once you get a saturated solution, no more crystals will dissolve, they'll just sink to the bottom of the bucket. Don't let them mix sulfamic in hot water. That's a way to boost the amount that's dissolved and thus boost the "strength" of the acid. They need patience and multiple acid applications with this cleanup, this is not a one-shot attempt.

My slate is fairly rough... just keep doing coats of sealant till the slate won't absorb it anymore. Sure it takes a little more effort to wipe off than others but on the flip side it takes a lot more dirt before its visible. Just use a rag or scrubber brush instead of a sponge if something is really stuck (scrubbing rough surfacee with the sponge will just chew up the sponge) My kitchen has been done for 2 years and the slate looks exactly same.

Daltile's Franciscan Slate is so realistic and looks so much likereal slate you'll find yourself reaching down to touch it to confirm the depth of the fissures depicted. I've got the Coastal Azul in my master bath, and it is fantastic. It's a type IV for variation, so you get the look of highly variable natural slate with the ease of care of commerical-rated porcelain. It also comes in a wide range of sizes/finishing pieces. It's so realistic that DH and I joke about showering in 'the cave'.

We have a rustic slate bathroom which I love and am extremely happy with. That said many of the comments made here about it are legitimate thoughts to consider. The tiles are uneven, and if a tiler without a lot of experience laying slate does the job, you could have bumps in areas of the flooring that won't appeal to your feet. It can run cold, but that has not been an issue for us even in sub zero weather, it's just not something we care about. It's very hard and can be hard on one's legs if you're standing for a long period of time. The pro's are that it's very low maintenance though, seldom shows dirt and super easy to clean when it does which was important to me. I don't agree with Lakeeffect in that you don't have to get Vermont Slate. If you research it at all, you'll find there are lots of different types of slate that will work fine. We didn't get Vermont slate. I did however take the suggestion of a pro in the bathroom forum and soaked some tiles in a bucket of water for several days to see if they would break down. It didn't and it's done amazingly well in all areas including the shower. These are old pictures from our remodel just after the install and sealant. It's called Indian Autumn and the pictures don't really do it justice. We wanted everything we've upgraded with to be of natural materials and earthy, so we didn't go with a porcelain, but if it's not something you care about, I think that the Daltile would be a good alternative.