Case 1

Cause of Defects

Basement walls and floors must be protected from the hydrostatic head of water and must also be able to control the movement of moisture by diffusion and capillarity action from the soil into the basement.

However, concrete is not waterproof. It consists of micropores formed during the migration of excess water during the hydration process. As the excess water dries off, they form channels or capillary pores. When subjected to water pressure, the pores allow the passage of water, resulting in seepage. The porosity of concrete, coupled with crack lines, allows the ingress of water, and, when re-surfaced, may result in the formation of efflorescence (deposit of salt) and/or calthemite (deposit of calcium carbonate). This is exacerbated by the formation of cracks due to the weak tensile strength of concrete against stresses resulting from shrinkage, differential settlements, etc.

The figure below shows a basement wall that has just undergone chemical injection despite previous patching repairs. Leaching of the chemical indicates cracks at porous areas and along the interface of the previous repair patches. The figure below shows plastic packers installed at weak areas earmarked to receive the chemical injection to seal off any paths that facilitate water entering into the inside surface of the basement wall.