Moisture entry through retaining foundation walls

Cause

Ground moisture has moved through a retaining wall as it is unlikely the wall will have been waterproofed, and there is:

  • no perforated drainage pipe at the base of the wall for ground water removal
  • no drainage gravel above the drain, resulting in the drainage pipe becoming blocked with silt
  • no filter fabric between drainage gravel and the drain, resulting in the drainage pipe becoming blocked with silt
  • the drainage behind the wall has stopped working due to the pipe being blocked or the drainage gravel becoming filled with fine soil material

Repair

  • install a drainage channel at ground level to intercept and drain the surface water
  • if it is not possible to dig out and expose the basement wall, apply a water-based epoxy coating to the inside face of the wall to stop moisture entry. This may reduce the amount of water passing through the wall
  • if possible, dig out and expose the back of the retaining wall:
    • check the drainage pipe for blockages; clear by flushing out with high pressure water
    • install a perforated drainage pipe at the base of the wall if necessary; place pea gravel around the pipe and lay a geotextile filter fabric over the gravel
    • seal the exposed wall with a waterproof coating or membrane
    • protect the waterproof membrane with sheet material such as polystyrene
    • line both excavated face and face of basement wall with B19 grade geotextile fabric
    • backfill to ground level using a free-draining granular fill
  • as a last resort, provide a drainage and collection channel in the subfloor where there is a significant amount of water and drain it to the outside, and increase the level of subfloor ventilation