Repairs to Concrete Water-Retaining and Water-Excluding Structures: Introduction

The usual reason for repairing a water-retaining or water-excluding structure is to remedy leakage. To avoid unnecessary repetition, these two types of structure will be referred to throughout this section as water-retaining structures and basements respectively.

The leakage may be:

(a) outward from the structure, e.g. from reservoirs, swimming pools, sewage tanks etc.;

(b) outward when the structure is full and inward when it's only partially full or empty, e.g. reservoirs, etc.;

(c) inward from the surrounding ground, as in the case of a basement.

Associated with any form of leakage, particularly when the structure has been in use for some years, is likely to be the corrosion of the reinforcement and spalling and cracking of the concrete.

It must be realised that in practice, no concrete structure will be what is known as ‘bottle tight’, unless it's lined with a waterproof membrane. When the structure is properly designed and constructed the amount of leakage should be very small; the amount that can be tolerated will depend on the circumstances of each case. Loss of water from water- containing structures is closely connected with a leakage test, which is normally applied to all new structures. This test is discussed in some detail later in this section.

In the case of basements there can be no prescribed water test as such, but basements are expected to be dry. Although in theory, a basement in reinforced concrete can be constructed so as to be completely watertight without resort to tanking, the author’s experience is that this desirable aim is unlikely to be achieved in practice. Those responsible for the design of a basement should give very careful consideration to the standard of watertightness required; the design and specification should then be prepared accordingly.

A fundamental principle of repair is to seal the leaks on the water face. Unfortunately this is not always possible, and specialized firms have developed techniques for sealing leaks on the ‘wrong’ side, that's against the flow of water. However, due to the basic difficulties in executing such repairs, guarantees of complete success are seldom offered; if they are, they should be read with great care. When it's proposed to carry out waterproofing work to the inside face of basements, consideration should be given to the possible use of pressure grouting to supplement the surface sealing. The object of the grouting is to help prevent the water penetrating into the body of the wall.

In the case of old reservoirs, the argument is sometimes advanced that the cost of the water lost by leakage is small compared with the cost of the necessary repairs. This may well be so, but consideration should also be given to the possible effect on the foundations and stability of the structure, by the continuous flow of several thousand gallons per day through the walls and floor.