During the crazy rains we have had here in Illinois the last month we discovered several leaks in the basement walls of our 1912 concrete foundation house. The worst leak was coming in my son's room, so much so that it continued seeping for six days after the rain had stopped. While grading issues need to be resolved on one side of the house, we discovered what we think is the cause of the continued leak in my son's room: a deck had been built off the back of the house over what used to be a basement access stairway/door. The previous owner, wanting to create a closet where this door was, removed the door and filled the hole in with cinderblocks and mortar(did a decent job of it too, it appears!).
However.....it seems that after creating the cinderblock wall and before building the deck he then filled in the exterior stairway with rocks, stones and loose soil! He then covered the rest of the formerly grassy area under the deck with rocks. We have yet to dig too deeply into the former stairs area, but we removed about two feet of top rocks and have yet to encounter any hardpacked soil. My impression is that he has created a cistern for holding rainwater by not filling in the area with real dirt that would then compact and create a barrier to the water---is that correct? When we looked behind the drywall in the basement it was obvious that water was seeping into the room at the seam of the foundation and the cinderblock wall.
We are going to remove the deck planks above this area and dig out all the debris he threw in there. Once we do that we'd like to add some waterproofing to the cinderblock wall--what would be the best material to use? Most important: what then would be the best thing to fill in the stairway with? Dirt? Any help here would be most appreciated.