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Thin coat stucco methods:
This article discusses the specifications for thin-coat stucco building exterior wall installation.
This article series discusses best practices construction details for building exteriors, including water and air barriers, building flashing products & installation, wood siding material choices & installation, vinyl siding, stucco exteriors, building trim, exterior caulks and sealants, exterior building adhesives, and choices and application of exterior finishes on buildings: paints, stains.
In an effort to speed up stucco application time and simplify
the process, several manufacturers have introduced
proprietary thin-coat stucco systems variously referred to
as one-coat, two-coat, thin-coat, or fiberglass-reinforced
Our photo of a thin-coat stucco wall being constructed (left) was at a Barnes and Noble bookstore in Poughkeepsie, NY.
All these systems apply a single base coat and a
top coat with a total thickness of 2/8 to 1/2-inch, compared to
7/8 to 1 inch for traditional three-coat stucco. The thinner finish
weighs from 5 to 6 pounds per square foot, compared
to 9 pounds for three-coat, and it is cost-competitive with
Like traditional three-coat stucco, thin-coat is applied
over wire mesh or expanded metal lath by hand or pump.
It is backed up by a waterproof drainage plane consisting
of Grade D building paper, integral flashings, and a weep
screed along the top of the foundation to drain away any
Some manufacturers, such as United States Gypsum,
have introduced hybrid systems in which the stucco is applied
to a cementitious board rather than to wire mesh. The
advantage is that cement board is impervious to moisture.
The drainage plane, and in some cases a layer of foam
insulation, lies behind the cement board.
Thin Coat Stucco Application Procedure
The base coat in thin-coat systems has
acrylic polymers and chopped fiberglass added to increase
its strength and resistance to shrinkage cracking and to
The base coat is premixed with only
sand and water added at the job site. Most contractors
using these systems apply an elastomeric color coat, similar
to a thick acrylic paint with fine aggregate, and formulated
to bridge small gaps less than 1/16-inch.
a smoother finish that is more water- and stain-resistant
and less prone to cracking than a traditional stucco. The
top coat can also be a traditional cement stucco finish.
Most of these systems require a 24- to 48-hour moist
cure and a total of six or seven days of curing before the top
coat is applied. Some require a primer for acrylic finishes.
Our thin-coat stucco wall damage photo (above-left) shows the vulnerability of this system to damage by common events at or around a building: in this case the use of a weed-whacker to trim growth close to the building wall. This EIFS installation is also installed so close to the ground as to invite insect attack on the structure.
To their credit, properly applied onecoat
systems are more waterproof and less prone to shrinkage
cracking than traditional stucco. It is easier to obtain a
uniform color and texture with the synthetic color coat
than with a traditional cementitious finish coat.
customer prefers the uniform color of a synthetic finish or
the more muted and variable color of cement stucco is a
matter of taste.
Our photo of a leaky stucco window sill on a New York home (left) shows a damaged, leaky sill where plastic mesh was used as a modern substitute for expanded metal lath.
On the downside, one-coat systems are less impact resistant
than traditional three-coat stucco. And with a
thickness of only 3/8-inch, one-coat systems are less able to
hide irregularities in the framing and are more likely to
have thin spots that are prone to problems.
Also, one-coat stucco systems are not completely waterproof. Over time, water
will find its way in at joints, penetrations, or cracks, and
the synthetic stucco will be slower to dry out than the more
permeable traditional stucco.
Finally, each system is proprietary and must be installed
according to the manufacturer’s approved specs and
details, which vary from system to system. Otherwise,
warranties are voided and code approvals, which are based
on building code evaluation reports, are invalid. For both
reasons, contractors should avoid mixing and matching
components from different thin-coat systems.
Exterior Insulation and Finish Systems Suppliers
Dryvit Systems Contact DryVit directly at
Dryvit Systems, Inc.
One Energy Way
PO Box 1014
West Warwick, RI 02893
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