Looking to purchase a very old home that has been updated but basement floor showing some moisture in one area even after - sump pit added, installed perimeter tile on all four walls of the basement, added a floor drain which tied into the perimeter tile that goes to the sump pump, installed a new sump pump, tied in all the downspouts and gutters underground to be taken to the street and added soil on the side (closest to the neighboring house) to have a positive grade and dry locked the four walls. Will a dehumidifier work to solve this problem or is there a bigger concern? No water just a damp spot in a line in the center of the basement floor. I believe the house was built on dirt and does not have a gravel base - it was built that long ago.