Every time we get a substantial rain, I can always count on at least a half-inch of rain in my basement. I've applied concrete sealant to the walls, but it doesn't seem to help. Where should I be looking to find the leak source that is causing my wet basement?
Darren A. ~ Milwaukee, Wisconsin
Water leaks can be very difficult to locate as water can travel quite a distance from where it is actually coming into your home. The first thing to check is whether your basement walls are damp or wet after a rain, or if water is only evident on your floor. If your walls are wet, take a look at the level where the dampness seems to start. Walls that are damp at the very top might indicate that the water is intruding at the next level up, such as around a window or door, or at a door threshold that isn't caulked properly.
Walls that are damp only part of the way up might indicate a hairline crack in the foundation, or possibly at the point where a utility might be penetrating the wall.
The fact that you are getting at least 1/2 inch of water after every rain indicates that the water may be coming through where the slab meets the exterior walls, or possibly around a column base. All basements will have water around them after it rains, and if the water is allowed to sit against the foundation, it can eventually find its way in regardless of how much water proofing you have on your wall.
Check your exterior grade to make sure the grade slopes away from your foundation on all four sides, and that there are no depressions that are allowing water to pond in one particular area. If your grade is fine, the next place to check is your foundation drain. If you have a partially buried basement where one side is not below grade, there may be a foundation drain that should be daylighted on this open side. When contractors install foundations, they place drain tile piping around the outside of the foundation walls. This piping is at the base of the walls, and allows accumulating water an escape route other than into the basement. If the ends of this piping get clogged up, it can prevent the water from escaping and cause it to go into your basement.
The last item to check is whether your sump pump, if you have one, is working properly. Most sump pumps come on automatically when the water reaches a certain level in the pit. If you have a pump, make sure it is coming on, and check the discharge point to make sure water is being removed.
After checking all of these areas, if you don't find an obvious problem that can be corrected, it may be time to call in a contractor. There are contractors that specialize in correcting wet basement problems.