I messed up and bought a non-vitreous, unglazed chair rail for use in the shower. The description says it is travertine. My husband is installing it DIY and has installed about 3/4 of it. It runs around the shower perimeter at 61" from the floor. My husband is very handy, but this is his first tile job and it is taking him a long time.

Shall I brave peril, ask him to take it down, and try to find something else? Or will I be OK with annual sealing? Do I seal before grouting?

If the chair rail's OK, can I use a 2x2 of another non-vitreous tile for the niches (back, sides, top & bottom? It looks like the same stone but the description does not say it's travertine. The niches are on the wall opposite the showerhead, 39" and 65" from the floor.

The chair rail at Lowes.com

The potential niche tile at Lowes.com

Thank you!!