Damp Basement Basics: Four Strategies for Drying the Drips

Mold. Mildew. Rust. Rot. Yuck! A damp basement brings all these plagues into your house, and more. The excess moisture can damage tools and furnishings, make a prime workshop or rec room space unusable, and even endanger your health. Studies show that the spores released by basement mold can trigger allergy attacks and cause respiratory problems.

Fortunately, it’s easy to handle many of the things that cause damp basements. The two most common causes are condensation inside and poor drainage outside. The quick way to figure out which one you have is to perform this simple three-step test.

  1. Tape a 24-inch-long piece of aluminum foil (here is a heavy-duty one from Amazon )to the wall in an area where you think dampness may be accumulating or coming into your basement. Run duct tape around all four sides, sealing the foil against the wall.
  2. Leave the foil in place for at least 48 hours.
  3. Remove the foil and see which side is wet.

If the side facing the wall is wet, water is penetrating through the wall from outside. If the side facing the room is wet, the problem is condensation. Let’s deal with condensation first, since it’s easier to fix.

Controlling Condensation

Condensation happens when moisture condenses out of the air and collects on the coldest surfaces in the basement, including the walls. You’re likely to notice it most during humid spring and summer months. There are two fixes for basement condensation problems: insulation and dehumidification.

Start by insulating surfaces that are likely to attract condensation—cold water pipes, bare air conditioning ducts and well tanks. Cover pipes with lengths of preformed foam pipe insulation, which is available to fit different pipe diameters. Wrap everything else with vinyl-faced fiberglass insulation. This comes in blanket form (like the insulation available for water heaters) and in rolls. The facing is important: it acts as a barrier and keeps moisture from soaking the fiberglass. When everything is wrapped, seal the open seams with duct tape.

The second part of this fix? Install a dehumidifier to remove excess moisture from the air. Locate the unit in the dampest part of the basement, at least 12 inches from walls or other obstructions that might interfere with airflow. For maximum dehumidification, buy a model that can run continuously during periods of high humidity, and connect its collection reservoir to a floor drain. Otherwise, the dehumidifier will turn off automatically when its collection pan or reservoir is full of water.

Dealing with Drainage Problems

  • Poor drainage is the leading cause of basement water problems. It can occur for several reasons, including:
    Missing or improperly installed rain gutters and downspouts. A heavy rain can dump massive quantities of water on your house, and runoff from the roof can collect around the foundation. To direct runoff away from the house, install gutters along all the eaves and attach downspouts equipped with strainers. to keep them clog free. Put down cement or stone splash blocks where downspout flow is heavy, and use corrugated pipe or downspout extensions to carry water away from the foundation.
  • Improper grading. If the ground slopes toward the house rather than away from it, water can pool by the foundation and leak inside. Also, if the soil is too close to the mudsill (also called a sill plate) running along the top of the foundation, you can end up with wet walls and even a rotted mudsill. Ground level around your home should be at least 6 inches below the mudsill.
  • Improper grading around basement window wells. Keep the soil at the bottom of a window well at least 6 inches below the windowsill. If this doesn’t solve the problem, you can buy and install a clear plastic window well cover to keep the rain out. If leaking continues, you may have to dig out the window well and install a drainage pipe to carry water to a lower point outside the foundation.

Plugging the Leaks

What if gutters, downspouts and regrading don’t cure basement moisture problems? Then you may have poor drainage below ground level, or a water source too close to the foundation. Since outside excavation and waterproofing is work you’ll want a professional to do, let’s focus on what you can do inside to stop leaks and keep water at bay.
Sealing the inside involves repairing crack and plugging any holes in the basement walls and floor with hydraulic cement, and then waterproofing the walls. Here’s how to proceed.

To repair cracks and holes:

  1. Locate all large cracks and holes. Check the walls, the seam between the walls and floor, and the floor itself.
  2. Widen the cracks and holes. Use a two-pound hand sledge (check on Amazon) and a masonry chisel to enlarge the openings. This improves the bond between the hydraulic cement and the existing concrete. Undercut the edges to create dovetail-shaped openings. These will hold cement better than V-shaped trenches.
  3. Clean the openings. Remove loose concrete from the cracks and holes, and scrub them with a wire brush and water.
  4. Fill the cracks and holes. Hydraulic cement is incredible stuff. It expands and tightly seals openings, and can even stop flowing water. But it dries quickly—between 5 and 15 minutes, depending on the manufacturer. So, only mix as much as you can use during that time. To work best the mix should have a buttery thickness. That’s about 4 1/2 parts cement to 1 part water.

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