stone enhancer and sealant for sandstone

I did a mosaic using tumbled river stone and marble. I worked on a
fiberglass mesh, then set the mesh and mosaic into a large piece of
sandstone, using thinset. It is for a grave site.
My question is the following: is there a product which will act as both
stone enhancer and sealant? Or should I enhance, then seal?
The mosaic/stone will be outdoors in a wet climate (Pacific Northwest),
but next to no frost.

Thank You

Veronica