Page 121 - Construction Waterproofing Handbook

3.10 CHAPTER THREE
Painting or staining over penetrating sealers is not recommended, as it defeats the pur-
pose of the material. With film-forming materials, if more than a stain is required, it may
be desirable to use an elastomeric coating to achieve the desired watertightness and color.
Most film-forming materials and penetrates are available in semitransparent or opaque
formulations. If it is desired to add color or a uniform coloring to a substrate that may con-
tain color irregularities (such as tilt-up or poured-in-placed concrete), these sealers offer
effective solutions. (See Table 3.3)

Penetrating sealers
Penetrating sealers are used on absorptive substrates such as masonry block, brick, con-
crete, and porous stone. Some penetrating sealers are manufactured to react chemically
with these substrates, forming a chemical bond that repels water. Penetrating sealers are
not used over substrates such as wood, glazed terra cotta, previously painted surfaces, and
exposed aggregate finishes.
On these substrates, film-forming clear sealers are recommended (which are also used
on masonry and concrete substrates). These materials form a film on the surface that acts
as a water-repellent barrier. This makes a film material more susceptible to erosion due to
ultraviolet weathering and abrasive wear such as foot traffic.
Penetrating sealers are breathable coatings, in that they allow water vapor trapped in a
substrate to escape through the coating to the exterior. Film-forming sealers’ vapor trans-
mission (perm rating) characteristics are dependent on their solids content. Vapor trans-
mission or perm ratings are available from manufacturers. Permeability is an especially
important characteristic for masonry installed at grade line. Should an impermeable coat-
ing be applied here, moisture absorbed into masonry by capillary action from ground
sources will damage the substrates, including surface spalling.
Many sealers fail due to a lack of resistance to alkaline conditions found in concrete and
masonry building materials. Most building substrates are high in alkalinity, which causes
a high degree of failure with poor alkaline-resistant sealers.
Penetrating materials usually have lower coverage rates and higher per-gallon costs
than film materials. Penetrating sealers, however, require only a one-coat application ver-
sus two for film-forming materials, reducing labor costs.
Penetrating and film-forming materials are recognized as effective means of preventing
substrate deterioration due to acid rain effects. They prevent deterioration from air and
water pollutants and from dirt and other contaminants by not allowing these pollutants to
be absorbed into a substrate. (See Table 3.4.)

TABLE 3.3 Film-Forming Sealer Properties

Advantages Disadvantages
High solids content; able to fill Not effective in weathering
minor cracks in substrate
Opaque stains available to cover Not resistant to abrasive wear
repair work in substrate
Applicable to exposed aggregate Film adhesion dependent on substrate
finishes and wood substrates cleanliness and preparation