https://www.energyvanguard.com/blog...-You-Put-a-Plastic-Vapor-Barrier-in-Your-Wall
"" Enhancing drying vs. preventing wetness
Understanding moisture is one of the most important aspects of making buildings do their jobs properly and not fail prematurely. We know now that mid-twentieth century building science incorrectly ascribed magical properties to vapor barriers. Water vapor from indoor air wasn't the source of most moisture problems. Bulk water from deficiencies in drainage planes, flashing, and other moisture management details caused most of the problems.
Building science has progressed since then. We know that vapor barriers can cause problems, but we still have homes like the one in Charleston with poly in the walls. And we have $4 million dollar homes with poly on the walls, too. I saw the one below when Martin Holladay came to Atlanta last year. That's in the basement, but the kneewalls in the attic also were covered with poly.
Vapor barrier on a basement wall in a 4 million dollar home (with a ductopus!)
Our understanding now is that it's generally more important for wall assemblies to be able to dry than it is to block water vapor with materials like polyethylene. Here's what Bill Rose wrote in his book, Water in Buildings:
"Given the fact that a very small percentage of building problems (1 to 5% at most in the authors experience) are associated with wetting by water vapor diffusion, the argument for enhanced drying potential becomes much stonger."""
It's okay for pressure treated wood to come in contact with concrete.
You can also put a barrier between regular wood and concrete.
As for the rest of the story..........
For example: You could install an piece of PT plywood over the concrete ledge then install a decorative board over that for a shelf.
