Why maybe on backsplash?

Why no showers?

Why no exterior?

Here's the whole story.

Slate-ish is not hurt by water.

So why all the restrictions, you say?

The issues are with what water brings with it.  The surface it's applied to, and  the deposits left behind from the water are where the real issues start to arise.

Backsplash:
Slate-ish has a rough textured surface.  Cleaning dried on wet applied materials(read this as wet kitchen splatters, hard water deposits or soap film) from it is not something you want to deal with.  There will always be something left in-between tiles and in the crevasses of the surface.  Scrubbing it hard will likely begin to affect the coloring. You of course could do this with lots of patience and a very soft brush but don't say we didn't warn you.

Still thinking you want to try a shower or outside use?

Shower:
On top of the cleaning issue there is the backer, or more plainly, the surface Slate-ish is glued to. This surface must also be able to handle being constantly wet. So sheetrock is out. So is plywood. Also many  paints. That makes the list really short as to what is an acceptable material to mount it to. Cement board is about the only option.

So cement board it is then. Well unfortunately now we have the issue of a wall designed to get wet a lot,  actually being wet a lot. Every time the wall gets wet water gets behind the tiles. This isn't applied with adhesive squeeze out and grouted like a stone, ceramic or concrete tile. There are joints between the tiles, and gaps behind them. All these joints easily let water, and any dirt in the water, behind the tiles. Over time the dirt will build behind the tiles in the gaps since there is no way to get it out. Behind the tiles will dry very slowly. The combination of damp and dirty creates mold growth conditions. Not something you want for sure.

Exterior:
Maybe you are thinking of using it in some area outside that doesn't get wet very often. Say a desert climate where it only rains occasionally. So the moisture isn't a problem. Well now we get to deal with UV radiation.  Slate-ish can handle it. It gets a tan, or more specifically turns amber wherever it's not coated. But there are two problems here.

One: tan over the grey raw material comes out more green-ish than tan.

Two: the color coatings are not designed for UV exposure.  We of course could use UV stable colors but they are more expensive and often have higher toxicity than our water based colorings.  If the range of applications for successful exterior use were wider we could possibly justify this. But that just isn't the case.

So there you have it. The No's and Maybes of backsplashes, showers and exterior use.

We know all this because we have tried all this.
Making Slate-ish for over 12 years has helped us understand fully what it can and can't do.  This comes on handy. We won't tell you it can do something it can't just to make the sale.