How to Repair Basement Concrete Block Walls

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This crack in a concrete block basement wall requires immediate repair to prevent it from spreading.
This crack in a concrete block basement wall requires immediate repair to prevent it from spreading. (Image: Jupiterimages/Photos.com/Getty Images)

If you are looking at cracks in the exterior walls of your basement, you are looking at cracks in your foundation. Fortunately, over 95 percent of foundation cracks do not create a threat to the integrity of the building, according to the website Basement Questions. Generally, the most they can do is to let water seep into the building. The cracks still need to be repaired. A frequently wet basement wall can encourage mold, mildew and fungus, which reduce indoor air quality. People often repair cinder block wall cracks with the same caulk they seal windows or fill gaps between tub and bathroom wall with. Such caulk will not hold.

Things You'll Need

  • Safety goggles
  • Protective gloves
  • Chisel
  • Hammer
  • Warm water
  • Stiff brush
  • Dishwashing liquid
  • Injectable concrete epoxy resin
  • Epoxy resin injection gun

Chisel out the crack in such a way that you undercut it, creating a V-shape groove with the point of the V closest to the surface. Wear safety goggles and protective gloves. Use a chisel and a hammer. Make sure you chisel out the V-shape facing the right direction. If you simply make a V-shape in the concrete with the point on the inside of the crack, the repair materials will pop out.

Clean out the crack with a stiff brush to remove any loose material. Wash the concrete block adjacent to the crack with warm water mixed with a degreasing agent such as dishwashing liquid. Use 1 tbsp. of dishwashing liquid for every gallon of warm water. Rinse with clean water.

Inject concrete epoxy resin into the crack, beginning at the top and drawing the injection gun down along the crack to the bottom. Concrete epoxies expand as they cure, so they will fill the V you chiseled out and all of the adjacent pores in the concrete block. Unlike regular cement (which you should not use), the epoxies are formulated to be impervious to the alkaline chemicals in the concrete. They bond strongly enough to the concrete to withstand the weight of the water that could otherwise seep into the basement from the outside.

Tips & Warnings

  • Most brush-on waterproofing compounds are more effective if they are brushed onto the side of the wall that the water is coming from---in this case the outside of the foundation. This would require excavating the foundation---an immensely expensive job.
  • If you do decide to use a brush-on waterproofing compound on the inside of the foundation wall, make sure the wall is completely free of dirt, dust, grease and oil and are damp. Brush on the compound in two thin coats rather than one thick coat.
  • An epoxy resin injection gun looks a lot like a caulking gun but it is not. Be sure to get the proper tool for this job.

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