Older slabs were often constructed without moisture barriers ... Moisture Damage to Floors Installing any type of floor over concrete that isn’t sufficiently dry can be disastrous.

Moisture is something to be managed. A vapor barrier can cut down on earthy smells, mildew, and general humidity.

I love concrete floors, but they're not great for every space. A wood floor can be much more appealing, especially in chilly or drab areas. "Beyond the beauty, they also provide an acoustic bounce ...