Page 62 - Construction Waterproofing Handbook

2.26 CHAPTER TWO
TABLE 2.3 Comparison of Positive and Negative Waterproofing Systems*

Positive systems Negative systems
Advantages
Water is prevented from entering substrate surface Accessible after installation
Substrate protected from freeze-thaw cycles Concrete substrate is allowed to moist cure
Substrate is protected from corrosive Eliminates need for subslabs and well pointing for
chemicals in groundwater foundation waterproofing
Disadvantages
Concrete may not cure properly Limited to application of cementitious systems
System inaccessible for repairs after installation No protection from freeze-thaw cycles
Subslabs and well pointing necessary No protection of substrate or reinforcing steel from ground
for foundation waterproofing water and chemicals
*With all positive systems, concrete should cure properly (up to 21 days) before application of any waterproofing materials.

● Swimming pools
● Cooling tower basins
In new construction, where costs and scheduling are critical, these systems are partic-
ularly effective. They do not require a completely dry substrate, and concrete does not
need to be fully cured before application. This eliminates well pointing and the need for
water control during construction. These systems apply to both walls and floors at one
time, thereby eliminating staging of waterproofing operations. No subslabs are required
for horizontal applications in new construction preventative waterproofing installations.
Finally, in cases such as elevator pits, the waterproofing is completed almost any time
during construction as best fits scheduling.
All cementitious systems are similar in application and performance but repel water dif-
ferently by the proprietary additives of a manufacturer’s formulations. Cementitious sys-
tems have several mutual advantages, including seamless application after which no
protection board installation is necessary.
All cementitious materials lack crack bridging or elastomeric properties but are success-
fully applied to below-grade areas that do not experience thermal movement. However,
below-grade areas are subject to freeze-thaw cycling and structural settlement. If these
cause movement or cracking, a cementitious system will crack, allowing water infiltration.

Metallic systems
Metallic materials contain a mixture of sand and cement with finely graded iron aggregate
or filings. When mixed with water to form a slurry for application, the water acts as an
agent permitting the iron filings to oxidize. These materials expand due to this oxidizing,
which then effectively seals a substrate and prohibits further transmission of water through
the material. This system is one of the oldest methods used for waterproofing (first patented
in 1906) and remains today an effective waterproofing system. (See Fig. 2.35.)
Metallic systems are applied in two or three coats, with the final coat a sand and
cement mixture providing protection over base coat waterproofing where exposed. This
final coat seals the metallic coats and prevents leaching or oxidization through paints or