by Harrison McCampbell,
Improperly detailed EIFS joints
allowed water to soak into the structure of this
portico, with ugly and expensive results.
As an architect and frequent consultant on waterproofing and
building envelope failures, I see a lot of EIFS problems
involving water leakage and resulting structural damage. Given
the number of lawsuits involving these sorts of problems in
homes built over the past decade, you'd think that builders
would have learned the importance of water-shedding details.
But as I see almost every day, surprisingly few of them have.
Although that provides me with a measure of job security, it's
also frustrating because a little attention to a few key
details can eliminate a huge amount of trouble down the
Caulk and Backer Rod
The key to a trouble-free EIFS application is the maintenance
of a 1/2- to 3/4-inch gap wherever EIFS meets a non-EIFS
material, such as roofing, trim, or doors and windows. The
correct gap makes it possible to finish the exposed edges of
the expanded polystyrene — which should be backwrapped
with reinforcing mesh before the EPS is secured to the
sheathing — with a waterproofing application of base coat
when the rest of the finish goes on. Finally, the gap is filled
with soft plastic backer rod and a bead of compatible
Good caulk, bad
caulk. If it's going to last, the caulking has to be
done right. The surface has to be clean and dry, the caulk
space must be correctly filled with backer rod, and the caulk
joint itself must be properly tooled (see Figure 1).
1. Wherever EIFS meets another material, backer
rod must first be installed in the joint. This keeps
the caulk from adhering to the back of the joint and
allows it to stretch with building movements. A
correctly tooled caulk bead has an hourglass shape that
is about twice as wide as it is thick.
The backer rod serves two functions: First, it prevents the
caulk bead from adhering to the back of the joint, allowing the
caulk to flex in response to thermal expansion and contraction
and other building movements. If the backer rod is omitted, the
caulk will adhere to the back of the joint as well as the
sides, limiting its ability to stretch and guaranteeing
premature failure. Second, it controls the thickness of the
finished application of caulk, which should ideally be about
half as thick as it is wide.
More often than not, though, the caulk and backer rod are never
applied at all. (I'm always told, "They're in the truck.") That
was the case in the repair job photographed here, where the
polystyrene board was simply butted against the trim and other
surfaces (Figure 2).
2. Moisture-soaked EIFS was butted directly
against the gable-end trim in this photo. Water seeped
through the resulting crack and penetrated the gypsum
sheathing, which had turned to gray mud in some areas.
Note the impression of the reinforcing mesh on the
When you butt EIFS up against another material, the edge of
the EPS board is now exposed to water absorption, since there
is not enough space to apply the base coat. The caulking, if
used at all, has less than 1/16 inch of EIFS surface to adhere
to in order to seal against water entry.
I have even heard EIFS contractors try to defend themselves
in a failed application by pointing out that they had
diligently backwrapped the edges of the EPS board with mesh, as
required. But unless the mesh-wrapped edges are also embedded
in basecoat, this does no good at all (Figure 3).
3. The EIFS applicator backwrapped the edges of
the polystyrene with mesh, as specified — an
empty exercise, because the tight spacing made it
impossible to apply EIFS to the edges of the