Architectural Concrete Panels Moisture Protection
SlenderWall uses a face-seal double-caulking method and offers an optional
proprietary secondary water drainage system, H2Out.
Water Penetration: There are four forces that
move water through walls—gravity,
capillary action, kinetic energy and air pressure differences. Gravity will
move water through an opening that slopes downward; capillary action draws
water into small cracks or pores in building materials; kinetic energy refers
to water leakage through walls due to the force of wind-driven droplets impinging
on openings in the wall; and differences in air pressure will move water
from a high pressure area to a low pressure area in search of equilibrium.
water penetration by use of the face-seal method. This is accomplished by
completely sealing the exposed face. The concrete mix is designed to a higher
density (minimum 5,000 psi) and incorporates an integral concrete admixture,
which has proven to significantly reduce water penetration. Additionally,
all joints may use a single layer—or
in extreme cases, a double layer—of sealant applied from the exterior.
A secondary water drainage system exclusive to SlenderWall is H2Out,
which also can be utilized if so designed. Dow Corning and other major manufacturers
have warrantied the use of their sealants in H2Out applications. (Copies
of approval letters are available upon request.)
Water Vapor Penetration: Water in its gaseous
state (vapor) exists in practically all air. It is expressed as the percent
of humidity. The higher the air temperature and percent humidity are, the
higher its density and, thus, the higher its pressure. For instance, if the
outside air is 90° Fahrenheit and 75% humidity and the inside air
is 75° Fahrenheit and 20% humidity, then the outside air is higher
pressure than the inside air and it flows toward the lower pressure area.
Designing a true pressure-equalized wall system is cumbersome and expensive.
The alternative is to recognize pressure differences and construct a vapor
barrier in the wall system.
In hot, humid seasons, the vapor tends to migrate
from the exterior to the interior. If the climatic conditions exist where
this is a concern, then a closed-cell polyurethane insulation is put on the
interior side of the 2-inch concrete skin of SlenderWall. (See Material
and Component Section for Dow Corning).
In cold seasons, vapor tends to migrate from the interior to the exterior.
In conditions where this is a concern, a layer of plastic is field-installed
by others over the light-gauge steel studs on the interior before the drywall
Dew Point: A common concern when discussing vapor
transmission is the dew point— that point in a wall assembly where
a temperature change through the wall causes the vapor to condense. Since
a vapor barrier for vapor moving in either direction can be applied with
SlenderWall, the dew point is not a concern.