Fieldstone basement wall as a shower interior?

My hunch is that this would be a bad idea but my hope is that it’s doable with a robust sealant. It’s along a townhouse party wall, as well.

In the interest of optimizing space, rather than framing out a wall for a basement shower, I’d prefer to seal the foundation wall across a short span, not more than 48”, and have the fieldstone wall be the shower wall.

Is this a bad idea?