Page 114 - Construction Waterproofing Handbook

ABOVE-GRADE WATERPROOFING 3.3
TABLE 3.1 Waterproofing Systems Differences

Below-grade systems Above-grade systems
Hydrostatic pressure resistant Ultraviolet-resistant
Structural movement capability Thermal and structural movement capability
Most inaccessible after installation Breathable
Both positive and negative applications Traffic wear and weathering exposure
Mostly barrier systems Aesthetically pleasing
Drainage enhancement a must Freeze–thaw cycle resistant

Application of a clear water repellent will also reduce water penetration through the brick and
mortar joints. Such sealers also protect brick from freeze–thaw and other weathering cycles.
Thus, waterproofing exposed vertical and horizontal building components can include a
combination of installations and methods that together compose a building envelope. This is
especially true of buildings that use a variety of composite finishes for exterior surfacing such
as brick, precast, and curtain wall systems. With such designs, a combination of several
waterproofing methods must be used. Although each might act independently, as a whole
they must act cohesively to prevent water from entering a structure. Sealants, wall flashings,
weeps, dampproofing, wall coatings, deck coatings, and the natural weathertightness of
architectural finishes themselves must act together to prevent water intrusion (Fig. 3.1).
This chapter will cover vertical waterproofing materials, including clear water repellents,
elastomeric coatings, cementitious coatings, and related patching materials. It will also
review horizontal waterproofing materials including deck coatings, sandwich slab mem-
branes, and roofing.

VERTICAL APPLICATIONS

Several systems are available for weatherproofing vertical wall envelope applications. Clear
sealers are useful when substrate aesthetics are important. These sealers are typically applied
over precast architectural concrete, exposed aggregate, natural stone, brick, or masonry.
It is important to note that clear sealers are not completely waterproof; they merely slow
down the rate of water absorption into a substrate, in some situations as much as 98 percent.
However, wind-driven rain and excessive amounts of water will cause eventual leakage
through any clear sealer system. This requires flashings, dampproofing, sealants, and other
systems to be used in conjunction with sealers, to ensure drainage of water entering
through primary envelope barriers.
This situation is similar to wearing a canvas-type raincoat. During light rain, water runs
off; but should the canvas become saturated, water passes directly through the coat. Clear
sealers as such are defined as water repellents, in that they shed water flow but are not
impervious to water saturation or a head of water pressure.
Elastomeric coatings are high-solid-content paints that produce high-millage coatings
when applied to substrates. These coatings are waterproof within normal limitations of
movement and proper application. Elastomeric coatings completely cover and eliminate
any natural substrate aesthetics. They can, however, add a texture of their own to an enve-
lope system, depending on the amount of sand, if any, in the coating.