Fill A Gap In A Concrete Basement Wall And Apply A Waterproofing Agent

24 April 2017
 Categories: Construction & Contractors, Blog


If rainwater drips through a small gap in a concrete wall that is adjacent to one of the windows in your home's basement, you should improve drainage outdoors and fill the gap in the wall with patch by completing the following steps. After the patch has hardened, sand it until it has a smooth surface and apply a waterproofing agent to each wall's surface to protect them from moisture.


  • rake
  • topsoil
  • large shovel
  • gravel
  • window well covers
  • ladder
  • tube of concrete patch
  • caulk gun
  • putty knife
  • hand sander
  • medium-grit sandpaper
  • tack cloth
  • concrete cleaning agent
  • bucket of warm water
  • mixing stick
  • sponge
  • towels
  • painter's tape
  • drop cloths
  • clear waterproofing agent (designed for use on concrete)
  • paint tray
  • paint roller and frame
  • extension handle
  • narrow paintbrush

Improve Drainage Outdoors

Go outdoors and inspect the property that is adjacent to the basement windows. Use a rake to level the ground if necessary, and add shovelfuls of topsoil to depressions in the ground. Add a thin layer of gravel next to each window. Water will drain more quickly through gravel pieces than soil, preventing puddling from becoming an issue. If a window well surrounds the exterior of each window, purchase covers for them. Covers will block rainwater from entering each well.

Fill The Gap In The Wall

Go in the basement and set up a ladder next to the gap in the wall. While standing on the ladder, use a caulk gun to fill the gap with concrete patch. Move one side of a putty knife across the patch to flatten it. Wait several hours for the patch to harden. Secure a piece of medium-grit sandpaper to a hand sander. Move the sander back and forth over the hardened patch until the patch has a smooth surface. Use a tack cloth to remove sanding dust from the concrete.

Clean The Interior Walls And Apply A Waterproofing Agent

Mix a small amount of a concrete cleaning agent with warm water. Use a sponge to apply the cleaning agent to dirty concrete. Remove the cleaning agent with a clean sponge that has been dipped into a bucket of water. Wait for the concrete to dry, or wipe a towel across the clean surfaces. Cover molding or hardware with strips of painter's tape.

Lay drop cloths across the floor. Use a paint roller to cover the interior walls with the waterproofing agent. A narrow paintbrush can be used to cover small portions of the wall that are difficult to reach with the paint roller, such as around electrical outlets. After the waterproofing agent has dried, remove and dispose of the strips of painter's tape.

To learn more about basement waterproofing, check out websites like