We're installing Montauk Black honed slate tiles in our kitchen, and I'm wondering if we need to seal them. If so, do we do it before installation, or after installation and before grouting? We're leaning toward matching the grout to the tile, so could we alternatively seal the entire floor after grouting?

If we need to seal, what product would you recommend? The tiles are a charcoal grey and I don't want anything that makes them look darker or glossy/wet.

Thanks!