It's hard to get a mental picture. Grout sealer is for grout, it seals
it by soaking and creating a non-porous layer on top. If you didn't
use a waterproof grout mix on the shower floor that'll be a problem,
you may find yourself standing in the basement one day. Personally I
would use a plastic pan thing for a shower floor, it is more of a sure
thing and requires no maintenance. Not very upscale, I know.