I'm not sure if/how much concrete needs to breathe, but what about putting sheets of plastic down first?
I suppose it may cause mold if moisture gets trapped in between??????
I have done some polishing with my corded dremel tool, I have used the older cordless dremels and would not recommend them, 100% battery power fades fast, but battery technology has come a long way since then. I do recommend the corded version but not as a main tool, only for the tight spots...