Has the Movement Already Begun?
The quick and simple answer is yes. However, that wouldn’t
be the whole story. As most of my readers will already know
that three-coat 7/8 inch thick portland cement stucco is
required by ASTM C926 when portland cement stucco is applied
to metal lath. The use of thinner so called one coat systems
is a relative new innovation introduced in mass during the
last decade and coming back to haunt many contractors in
this decade. Failures in some one-coat stucco systems are
rampant as are the number of law suites involving some of
these systems. It seems that these failures have encouraged
some one-coat stucco manufacturers to encourage contractors
and owners to install these systems in 1/2 inch or thicker.
As a result of this evolution, let’s not through
out the baby with the bath water; meaning we shouldn’t
condemn the entire industry for a few poorly functioning
system. Sorry for the horrible cliché’, but
not all one-coat systems are failing and not all are involved
in law suits. Some manufacturers are giving instruction
classes and distribute quality installation manuals with
excellent details. Finally, many good systems fail because
of poor quality workmanship. We can’t hold the one
coat systems responsible if they design a good system and
it is installed poorly or incorrectly.
How did these one-coat stucco systems come into
existence?
It is my understanding that one-coat systems came into
existence as a means of competing initially against the
traditional soft coat EIFS. It was felt that traditional
three coat stucco was too expensive when compared to the
traditional EIFS systems and could not be competitive in
most areas of the United States.
How do you produce a stucco system that is less than half
the thickness of traditional stucco and still have a system
that will resist water intrusion, cracking and delamination
to the same degree as traditional three-coat stucco. The
answer for some manufacturers of these systems was to sell
only in bags that contain traditional stucco components
plus some percentage of additives like acrylic modifiers
and chopped alkali resistant fiberglass fibers. Finally,
these systems were to be finished with a traditional acrylic
troweled on finish of about 1/8 inch in thickness.
In theory this system had pretty good chances of success.
Improved flexural and structural strength from the acrylics
and fibers and a highly water resistant final coating that
offered a very good elongation factor to span small cracks
that might occur in the base coat all contributed to help
these companies defend their position.
So what happened to these systems to make some of
them fail?
The simple answer to that question is that some the systems
evolved in the wrong direction. Some companies reduced or
eliminated the acrylic modifiers and the amount of fibers
added to the mix. In some cases the installation instructions
were limited to brief bits of information in their approval
reports. Also, in some cases the contractor chose to add
more material to the bags to make them go further thus degrading
the premixed material. Finally, the troweled on acrylic
finish was replaced with thinner and thinner spayed on elastomerics
or even latex paint finishes. I even see some one-coat systems
with no finish coats on them. I have my doubts concerning
the long term water resistance of a 3/8” one coat
stucco application with out the protection of a reasonable
thickness of a good breathable acrylic finish or some equivalent.
I will be the first to note that many of the one-coat
stucco failures are caused by installer errors. It seems
that the most common errors are poor lapping techniques
involving paper backed lath with the paper falling between
the sheets of diamond mesh lath. This usually causes a thinning
of the already thin stucco application in these areas. In
fact I would have to list variation of stucco thicknesses
and lack of use of the proper accessories as the next two
most common errors in any stucco application.
Three-coat Stucco Resurgence in the Works?
In recent months I have seen something of a resurgence
in the use of three-coat stucco applications and not just
for commercial work. At least one major county in Florida
has mandated that all stucco on future work be done in three-coat
portland cement stucco exclusively. This decision was not
made lightly and will likely have an effect on other counties
in Florida. Perhaps it might be the beginning of a major
change in how we do stucco in this country. No longer will
we make construction decisions purely based on a monetary
basis only. Perhaps we will remember the old adage “Pay
me now or pay me later.” It has been my experience
that he latter decision is very costly to everyone involved.
If it were possible to properly train installers and then
inspect their work on a daily basis by qualified inspectors
we would see the quality of stucco in this country improve
drastically. Perhaps then there would be a place for the
well thought out and designed 0ne-coat stucco systems. However,
as long as the quality of workmanship does not improve and
is not consistent we will continue to see problems with
all stucco. Read ASTM C1063 and C926 and the Metal Lath
Handbook available on this web site for further information
on the correct application of metal lath for portland cement
stucco applications. Work with a good reliable one-coat
manufacturer. Look for a manufacturer that trains applicators
thoroughly and has literature that reflects their willingness
to support you in your effort to do quality work and produce
a quality job.
Lets all work to make our industry as great as it can
be.
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