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Foundation Problems & Solutions

Concrete Foundation Walls - Water Leakage

Problem: Condensation on interior of foundation walls.

Cause: Inadequate damp-proofing.

While some condensation on foundation walls in spring and summer can result from interior humid air contacting cooler surfaces, excessive condensation or moisture in basements is often the result of the movement of soil moisture through the foundation wall and floor slab. Builders should not confuse the role of damp-proofing with that of waterproofing. Damp-proofing is intended to prevent the flow of water vapor in the soil. It is not intended to prevent water leakage through cracks and holes in the wall.

Solutions: Ensure that damp-proofing is effectively installed on foundation walls and under floor slabs.

  • Brush walls to remove dirt, dust, oils and scale before you apply damp-proofing materials.
  • Spray or roll on two coats of damp=proofing at right angles to grade level on the exterior. The damp proofing should be carried over the top of the footing. Ensure that the final coat of damp-proofing is firm before you backfill as shown in Figure 27.
damp proofing foundation walls and slabs
Figure 27 - Damp-Proofing Foundation Walls & Slabs
  • Consider the use of exterior membrane materials which serve as effective replacements for damp-proof coatings.

  • Provide damp-proofing under floor slabs to prevent moisture from seeping through slabs. Polyethylene 6 mil (o.15 mm) or Type S roll roofing with joints lapped no less than 4 inches (100 mm) are acceptable options.

  • To prevent wicking of soil moisture up through the footing to the foundation wall, install damp-proofing materials over the footing before you pour the wall. Ensure that adequate bonding is maintained between the wall and the footing key as shown in Figure 28.
controlling capillary water
Figure 28 - Controlling Capillary Water