Page 60 - Construction Waterproofing Handbook

2.24 CHAPTER TWO

FIGURE 2.33 Installation of swell-type waterstop. (Courtesy of Vandex)

surfaces, mildew, and staining. Therefore, it is necessary to prevent or limit capillary
action, even when using waterproof membranes beneath slabs. Excavating sufficiently
below finished floor elevation and installing a bed of capillary-resistant soil provides
drainage of water beneath slabs on grade.
This combination of foundation drainage and soil composition directs water away from
a structure and is necessary for any waterproofing and envelope installation. Refer again
to Fig. 2.1 for recommended controls for proper surface and groundwater.

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 inte-
rior side from which water occurs. Examples are shown in Fig. 2.34.
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.
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 pro-
duces an opposite result—no curing of concrete, but protection of reinforcing steel and of
the substrate itself.