Lenore, who is installing the granite slab shower? Start there and make your priority be hiring a VERY experienced tile professional - one you have vetted carefully to insure that their qualifications meet your design requirements and product selections. Stone slab installations are not for the B team, and especially in a wet area. Can it be done? Yes, depending upon the structure over which a solid surface stone is installed and the methods used. We install solid surface shower walls regularly, but from an empty cavity which we build to meet all specific design and installation specifications, including the pan. A solid stone slab cannot be supported by the pan (it is not meant to support a slab wall). A slab wall is pinned and tied so it is self supported, not supported by a pan. This is a very complex installation. A LOT to consider. As one example, the thickness of your slab? 2cm. 3cm? (effects the weight load on the space). And I could go on. After you have carefully vetted the qualified tile contractor, have this conversation with them. If you question or want to clarify their recommendations, check back or seek professional advice from other qualified sources. Please consult with a professional onsite. Good luck with your project.

I have to say I'm a bit of a skeptic about using things like boiled linseed to seal stone tile: it would absolutely HAVE to leave an oily residue, and I wouldn't want the job of scrubing it off. I've used linseed on cedar, leather, etc.: great stuff in the right surface, but unquestionably greasey. There are a lot of folks who love this sort of 'home remedy' stuff, like using Bath oil for mosquito repellent. I tried that one: the mosquitos just land on you, stick to the oil and die. Real pleasant. I'd use a real stone sealer, something specifically created to do the job.

Staceyneil, I don't think tumbled would make it easier to cut. It's the makeup of the stone not the finish that makes it difficult. We have polished honey onyx mosaics on the shower floor and while they were hard to cut it was not impossible.(Not even close to impossible...for what it's worth, our guy first declared it was like cutting sugar cubes....but when it was done it was his favorite job) As to the color changing with grout? Absolutely not! It sparkles and oh boy, the translucent quality is just a joy.

This definitely looks like a sloppy silicone job. Call the company you hired back out to take care of this. If they are truly a "5-star" company, they will fix mistakes like these and do whatever it takes to stand behind their work! As for the basic principle of how "slab" shower systems work, in response to some of the comments above, the Onyx Collection product is designed to work with a proper 100% silicone application in the corners and expansion joints as part of the system's PRIMARY waterproofing. The walls are installed via use of 100% silicone both as an adhesive and as a "seam fill" in the corners and joints, preferably over a code-compliant WATERPROOF backer board like DensShield. Greenboard has a water-resistant face that is not waterproof; while the DensShield has a waterproof face. Our company has installed many Onyx systems, and we do them over DensShield, not Greenboard or any of its "water-resistant" analogues (there are many). The corners and joints must be fully and properly filled to maintain the primary waterproofing integrity of the system. In the unlikely, but possible, occurence that one or more of these joints ever fail (through inevitable expansion and contraction that naturally occurs), you need a totally waterproof board behind them. This generally differs from tile, where the PRIMARY and ultimate waterproofing layer is built behind the tile wall system. With tile, you still want to follow TCNA guidelines and use a properly-tooled bead of 100% silicone in all corners and joints (as opposed to grout, which will crack), as these places will expand and contract regularly. However, it is important to understand that the silicone application with a tile system will only serve as a SECONDARY waterproofing layer; it's primary purpose is to prevent visible cracks in corners and joints that you would get from using grout only. Many residential and commercial tile installations still have improper, grouted corners and joints, which is why they almost always have visible cracks in these areas.