The Metal Lath Newsletter
Volume 04, Issue 01, January 2004
Stucco Bands Can Lead to Major Water Intrusion
What are Stucco Bands?
Stucco bands are architectural reliefs in stucco applications
usually placed on large open expanses of stucco such as
walls at floor levels, around windows, or as wainscoting
to add an architectural flare to any stucco project.
The original stucco bands also known in some areas as pop
outs, were merely wooden planks of varying sizes that were
attached to the wall and covered in lath, corner beads,
and stucco cement. If and when the band leaked the wood
would rot and the lath would rust often causing a delamination
of the lath and stucco. Some contractors are now replacing
the wood with foam strips that are then covered with offset
leg corner beads and strip lath prior to the stucco application.
The wall and the bands are then stuccoed at the same time
to achieve full embedment and to avoid cracks at the juncture
with the wall. The top surface of the band should be sloped
down and away from the wall to allow for drainage.
While banding applications have evolved to include special
banding beads, or larger casing beads that are deeper than
the stucco on the wall surface. These beads are placed opposing
each other and then filled with stucco to form the band
which is usually 1/2 inch to over 1 inch higher than the
plane of the wall’s surface and are often finished
in a different color than the wall. What I see quite often
when the double casing bead method is employed are leaks
at the junction of the wall stucco with the top casing bead
or the casing on the outside edge of the window band. This
leak occurs when the stucco shrinks away from the bead about
1/32 inch during the curing process. The crack is too small
to accept a proper amount of caulking material to seal properly
and yet large enough to allow sizable amounts of moisture
to enter behind the cementitious membrane.
Also seen in the market place are bands that are placed
on the wall after the lath, scratch and brown coat are installed.
These bands can also be opposing casing beads that after
installation are fitted with a lath strip between the beads
and then filled with stucco. These can be problematic because
the application of the beads requires that they be mechanically
attached to the framing through the stucco that has already
been applied. They often have a flat top flange that does
not slope away from the wall and the bead has very little
area to caulk at the juncture with the wall. However, with
this application at least the water should not be able to
enter the wall or get behind the cementitious membrane.
At least one manufacturer of vinyl banding casing beads
manufacturers one that has a sloped surface to facilitate
the movement of water away from the wall.
Finally there are the EIFS types of foam bands that are
applied to the surface of the brown coat of stucco. In some
areas these can be purchased prewrapped and finished with
a colored EIFS finish. In other areas the band must be cut
to size, wrapped with fiberglass mesh and then finished
with an EIFS type finish. Once complete the band can be
attached with mastic to the surface of the brown coat and
caulked along the top edge. The top surface of these bands
should be sloped at least a few degrees, down and away from
the building to provide drainage and a drip edge. Although
these seem to be the best alternative for band installation,
if they are not sealed properly at the juncture with the
building they can leak behind the band and become detached
in time. Foam bands that are simply wrapped and covered
with the typical EIFS finish are not as durable as portland
cement stucco bands. However the tradeoff is somewhat justifiable
due to the reduced risk of water intrusion into the wall
If the Band Leaks what are the Possible Repercussions?
Band leakage as with all stucco leakage can be disastrous
to the overall wall system. However, if the entire system
was installed according to ASTM C1063 and C926 including
two layers of water resistant breathable building paper
that was correctly installed, proper flashing around all
openings in the stucco membrane that is complete and proper,
foundation weep screeds at the bottom of all framed walls
and if all of the other requirements of these codes have
been met, then the redundant systems should be in place
to make temporary small leaks rather insignificant. To say
that is not to minimize the long term effects of water intrusion.
It is imperative that a regular maintenance and inspection
system be put in place after the job is complete by the
project owner or their representatives to find and correct
stucco leaks before they can cause catastrophic failure
of the stucco system including the building paper and the
sheathing and structural systems beneath.
Like all forms of construction cladding stucco requires
maintenance. Caulking will not last forever and must occasionally
be removed and replaced. Cracking to some extent is inevitable
with all stucco systems. This is not to imply that large
structural cracking is common. Rather it is important to
state that cracks do occur in stucco installations and are
not always the fault of anyone. Building movement, excess
wind loads, movement of other components that apply stress
to stucco can all cause cracks to occur. These cracks are
often minute and require no action at all. In some cases
however a structural crack that is wide and deep enough
to cause moisture intrusion will appear. These cracks are
generally wider than 1/8 inch and penetrate all layers of
stucco down to the lath. These cracks should be filled with
trowlable filler and patched as soon as they are discovered.
Furthermore, the underlying cause of the crack should be
investigated to see if more serious problems with the stucco
or structural systems exist.
The designer and installer should not shy away from bands
simply because they can be problematic, but rather should
look for the best system to install and then make sure that
the entire stucco system is installed correctly in compliance
to codes and ASTM C1063.
"The author offers no warrantees,
implied, stated, or expressed regarding the information
found in this article including techniques, construction
methods, drawings or materials identified in this article.
To the best of his knowledge the information within is correct
and up to date as of its publication date. The author is
not responsible for typographical errors. This article is
protected by all copyright laws and shall not be photocopied,
stored in any electronic format or distributed without express
written consent of the author. All rights reserved by Metal
Lath Consulting Co, LLC."
Coming in the next issue:
Accessories: Control Joints Part 2
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The answers to commonly asked metal lath installation questions
derived from job experiences and client questions.