WATERPROOFING: POSITIVE AND NEGATIVE SYSTEMS.

In new and remedial installations, there are both negative side and positive side below-grade systems. Positive-side waterproofing applies to sides with direct exposure to water or a hydrostatic head of water. Negative-side waterproofing applies to the opposite or interior side from which water occurs. Examples are shown in Fig. 2.34.

FIGURE 2.34 Below-grade positive and negative waterproofing details.

Although both systems have distinct characteristics, as summarized in Table 2.3, the majority of available products are positive-type systems. Negative systems are limited to cementitious-based materials, which are frequently used for remedial applications. Some materials apply to negative sides of a structure for remedial applications but function as positive-side waterproofing. These materials include chemical grouts, epoxy grouts, and pressure grouts. Admixtures (material added or mixed into mortars, plaster, stucco, and concrete) have both positive and negative features but are not as effective as surface-applied systems.

TABLE 2.3 Comparison of Positive and Negative Waterproofing Systems*

The principal advantage of a negative system is also its principal disadvantage. It allows water to enter a concrete substrate, promoting both active curing and the corrosion and deterioration of reinforcing steel if chlorides are present. Positive-side waterproofing produces an opposite result—no curing of concrete, but protection of reinforcing steel and of the substrate itself.

Positive and negative below-grade systems include

● Cementitious systems
● Fluid-applied membranes
● Sheet-membrane systems
● Hydros clay
● Vapor barriers