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EIFS Drainage systems:
This article discusses in-wall drainage systems introduced to avoid moisture and mold problems in EIFS synthetic stucco wall systems, and the role of weather and moisture in stucco wall installation, durability, and painting success.
This article series discusses best practices construction details for building exteriors, including stucco exteriors, exterior caulks and sealants, and choices and application of exterior finishes on buildings.
In response to these problems, most
EIFS manufacturers have introduced new “drainage” or
“water-managed” systems, which require the same type of
waterproof drainage plane found behind traditional stucco
systems (see Figure 1-30)
[Click to enlarge any image]
As with traditional stucco, layered building paper or
plastic housewrap protects the framing and sheathing, and
all exterior openings and penetrations are flashed to conduct
any water to the outside of the sheathing wrap.
window leakage was the single biggest contributor to EIFS
failures, pan flashing is recommended at windows.
Rather than gluing the EPS foam to the sheathing, the
new drainage EIFS typically use mechanical fasteners and
are designed with a capillary break between the back of
the EPS and the sheathing wrap to promote drainage.
EIFS contractors use special corrugated or wrinkled sheathing papers to create
the drainage space, while others have vertical grooves
cut into the back face of the foam insulation.
In all cases,
the drainage plane leads to a perforated weep flashing at
the foundation to drain away any trapped water.
Workmanship & EIFS Exterior Stucco Wall Success
The backup drainage layer, however,
should not provide an excuse for sloppy workmanship on
the exterior skin. The new kinds of EIFS should still be
made as waterproof as possible, since any water that leaks
past the skin may be slow to dry out. EIFS consultant
Russell Kenney, who has worked with these systems for
nearly 20 years, recommends exceeding the minimum
specs required by EIFS manufacturers.
On the other hand, our EIFS damage photograph (left) shows how water or moisture traps can form in an EIFS wall even in a building interior, leading
to substantial damage. (Photograph courtesy of home inspector John Rudy).
recommends a higher-density EPS foam with only 2%
water absorption by volume instead of the 4% allowed by
ASTM C584. In addition, Kenney recommends a heavier
6-ounce reinforcing mesh versus the typical 3-ounce cloth,
as well as special high-impact mesh in high-traffic areas.
He also recommends a 3/32-inch base coat applied in two
layers, with the first layer used to partially embed the
fiberglass reinforcing and the second layer to fully cover
and protect it.
These steps will significantly improve the
impact resistance of EIFS, but it is still less durable than
traditional stucco or thin-coat stucco.
See details about the cause, diagnosis, cure, or prevention of paint failures on stucco exterior walls, found at STUCCO PAINT FAILURES.
Apply Sealant to EIFS Base Coat
As with the original
barrier EIFS, all penetrations require a high-quality elastomeric
sealant. The sealant needs to be applied to the base
coat since the finish coat tends to soften when wet, providing
a poor substrate for sealant. For the caulk joints to last,
they must be wide enough to tolerate the anticipated movement,
typically 3/8 to 1/2-inch, and backed up by backer rod
(see “Joint Design,” page 37 in Best Practices Guide to Residential Construction).
While control joints are
generally not needed along the length of the wall—unless
it exceeds 75 feet and is in direct sun—they are required
between floors on multistory buildings. Silicone sealant is
recommended at all joints for its longevity and flexibility
in cold temperatures.
In theory at least, drainage EIFS should function the
same as any other exterior cladding systems. Any water
that manages to penetrate the outer skin should be stopped
by the drainage layer and safely drained away. However,
given the low permeability of polymer-based coatings and
the tendency of EPS foam to soak up and hold water, EIFS
are best avoided in residential projects unless high-quality
workmanship and regular maintenance of sealants can be
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