Plastic sheeting over basement dirt floor to combat moisture?
I'm hoping some of you more experienced old home owners will be able to clarify something for me. I have an 1857 home with a stone foundation and a dirt floor in the basement. During the pre-sale home inspection, the inspector told me I ought to invest in some plastic sheeting or tarps and lay them over the dirt floor and also the stone walls of the basement to help keep moisture at bay. It seems to me that this would only trap moisture, though. Has anyone ever heard of doing this and if so, is it a good idea or a bad idea?
For the record, I haven't noticed any moisture problems in the basement. There is an addition on that basement from the 1940s that is poured concrete floor and foundation. I do notice dark (damp but not wet) spots on the concrete floor when I forget to keep the dehumidifier on, but otherwise it's dry and odor-free down there. There is efflorescence in a few spots on the walls of the 1940s concrete basement, but nothing at all in the 1857 stone/dirt basement area. We do have the dehumidifier set to go on automatically when the humidity reaches a certain point.