Page 130 - Construction Waterproofing Handbook

ABOVE-GRADE WATERPROOFING 3.19
material to bond to it directly. Therefore, projects sealed with these materials can not be
painted over in the future without having to remove the sealer with caustic chemicals such
as solvent paint removers. This can create problems on projects where some applications
are required over the substrate once sealed, such as parking-stall painted stripes in a park-
ing garage. Manufacturers of the silicone rubber sealers should be contacted directly for
recommendations in such cases.
These materials generally have excellent repellency rates in addition to acceptable per-
meability rates. Overspray precautions should be taken whenever using the product near
glass or aluminum envelope components, since the material is difficult if not almost
impossible to remove from such substrates. (See Table 3.10).

Sodium silicates
Sodium silicate materials should not be confused with water repellents. They are concrete
densifiers or hardeners. Sodium silicates react with the free salts in concrete such as cal-
cium or free lime, making the concrete surface more dense. Usually these materials are
sold as floor hardeners, which when compared to a true, clear deck coating have repellency
insufficient to be considered with materials of this section.

TABLE 3.9 Siloxanes Water-Repellent Properties
Advantages Disadvantages
Not susceptible to alkali degradation Not applicable on natural stone substrates
Bonds chemically with substrates Can damage adjacent substrates and vegetation
with high permeability rating
High repellency rating and excellent Cost
penetration depth

TABLE 3.10 Silicone Rubber Water-Repellent Properties

Advantages Disadvantages
Application to a wider range of substrates Cannot be painted over
including canvas and wood Can damage other envelope components
Bonds integrally with substrate such as glass or aluminum
Can fill minor cracks and fissures

WATER-REPELLENT APPLICATION

General surface preparations for all clear water-repellent applications require that the sub-
strate be clean and dry. (Siloxane applications can be applied to slightly damp surfaces, but
it is advisable to try a test application.) All release agents, oil, tar, and asphalt stains, as well
as efflorescence, mildew, salt spray, and other surface contaminants, must be removed.
Application over wet substrates will cause either substrate discoloring, usually a white film
formation, or water-repellent failure. When in doubt of moisture content in a substrate, do a
moisture test using a moisture meter or a mat test using visquene taped to a wall, to check for