Sounds like moisture. Tape some plastic over the area to check. Do everything you can to solve the moisture problem first. Gutters, roof leaks, pipes, condensation, soil grading, etc. Then I'm thinking maybe a basement waterproofing type of primer. That's the only thing I can think of that will resist any kind of hydraulic pressure. I don't see how drywall or skim coating would solve the problem unless that water has someplace else to go. That's an old house.