I live mid-block (houses on both sides), in a 1906 city row house with brick basement walls and a cement floor. We never have water in the basement. We have dark spots that get lighter and darker but never 100% go away. They are clearly moisture that is coming up through the floor at certain places.
Tests have shown the cement is about 33% wet in those dark spots. They are all at the front of the house. Outside, the tiny front yard is field stone and slopes away from the house, so no water is getting down around the front foundation. In the back, the outside level matches the interior and there is no standing water there (and no dark spots at the back of the house anyway).
What is causing the dampness and what can I do to stop it...before I finish the basement as usable space?