Page 118 - Construction Waterproofing Handbook

ABOVE-GRADE WATERPROOFING 3.7
All these exposure problems must be considered when choosing a system for water-
proofing above-grade envelope portions. Above-grade waterproofing systems include the
following horizontal and vertical applications:

● Vertical
● Clear repellents
● Cementitious coatings
● Elastomeric coatings
● Horizontal
● Deck coatings
● Clear deck sealers
● Protected membranes

CLEAR REPELLENTS

Although clear sealers do not fit the definition of true waterproofing systems, they do add
water repellency to substrates where solid coatings as an architectural finish are not accept-
able (see Fig. 3.2.). Clear sealers are applied on masonry or concrete finishes when a repel-
lent that does not change substrate aesthetics is required. Clear sealers are also specified
for use on natural stone substrates such as limestone. Water repellents prevent chloride ion
penetration into a substrate and prevent damage from the freeze–thaw cycles.
There is some disagreement over the use of sealers in historic restoration. Some prefer
stone and masonry envelope components to be left natural, repelling or absorbing water
and aging naturally. This is more practical in older structures that have massive exterior
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wall substrates than in modern buildings. Today exterior envelopes are as thin as 8 inch,
requiring additional protection such as clear sealers.
The problem with clear sealers is not in deciding when they are necessary but in choos-
ing a proper material for specific conditions. Clear repellents are available in a multitude of
compositions, including penetrates and film-forming materials. They vary in percentage of
solids content and are available in tint or stain bases to add uniformity to the substrate color.
The multitude of materials available requires careful consideration of all available prod-
ucts to select the material appropriate for a particular situation. Repellents are available in
the compositions and combinations shown in Table 3.2. Sealers are further classified into
penetrating and film-forming sealers.
Clear sealers will not bridge cracks in the substrate, and this presents a major disad-
vantage in using these materials as envelope components. Should cracks be properly pre-
pared in a substrate before application, effective water repellency is achievable. However,
should further cracking occur, due to continued movement, a substrate will lose its water-
tightness. Properly designed and installed crack-control procedures, such as control joints
and expansion joints, alleviate cracking problems.
Figure 3.3 shows a precast cladding after rainfall with no sealer applied. Water infil-
trating the precast can enter the envelope and bypass sealant joints into interior areas.
Figure 3.4 demonstrates just how effective sealers can be in repelling water.