Page 126 - Construction Waterproofing Handbook

ABOVE-GRADE WATERPROOFING 3.15
effective on very porous surfaces such as lightweight concrete block. The surface of this block
contains thousands of tiny gaps or holes filled with trapped air. The acrylic coatings cannot
displace this trapped air and are ineffective sealers over such substrates. (See Table 3.5.)

Silicones
Silicone-based water repellents are manufactured by mixing silicone solids (resins) into a
solvent carrier. Most manufacturers base their formulations on a 5 percent solids mixture,
in conformance with the requirements of federal specification SS-W-110C.
Although most silicone water repellents are advertised as penetrating, they function as
film-forming sealers. Being a solvent base allows the solid resin silicone to penetrate the
surface of a substrate, but not to depths that siloxanes or quartz carbide sealers penetrate.
The silicone solids are deposited onto the capillary pores of a substrate, effectively form-
ing a film of solids that repels water.
All silicone water repellents are produced from the same basic raw material, silane.
Manufacturers are able to produce a wide range of repellents by combining or reacting dif-
ferent compounds with this base silane material. These combinations result in a host of
silicone-based repellents, including generic types of siliconates, silicone resins, silicones,
and siloxanes. The major difference in each of these derivatives is its molecular size.
Regardless of derivative type, molecular size, or compound structure, all silicone-based
repellents repel water in the same way. By penetrating substrates, they react chemically
with atmospheric moisture, by evaporation of solvents, or by reaction with atmospheric
carbon dioxide to form silicone resins that repel water.
Only molecular sizes of the final silicone resin are different. Silicone-based products
require that silica be present in a substrate for the proper chemical actions to take place.
Therefore, these products do not work on substrates such as wood, metal, or natural stone.
A major disadvantage of silicone water repellents is their poor weathering resistance.
Ultraviolet-intense climates can quickly deteriorate these materials and cause a loss of
their water repellency. Silicone repellents are not designed for horizontal applications, as
they do not resist abrasive wearing.
Silicone repellents are inappropriate for marble or limestone substrates, which discolor
if these sealer materials are applied. Discoloring can also occur on other substrates such as
precast concrete panels. Therefore, any substrate should be checked for staining by a test
application with the proposed silicone repellent.
Lower-solid-concentration materials of 1–3 percent solids are available to treat sub-
strates subject to staining with silicone. These formulations should be used on dense surface

TABLE 3.5 Acrylic Water Repellent Properties
Advantages Disadvantages
High solids materials can fill Poor weathering resistance
minor substrate cracks and fissures
Stain colors available; compatible Can pick up dirt particles during cure stage
with patching materials
Breathable coating, allows Poor crack-bridging capabilities
vapor transmission