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 Stucco, a Portland-cement-based mixture, is a common exterior wall
treatment commonly found throughout much of the western United States and
parts of the South in Texas and Florida. In general, when applied
properly, a stucco exterior requires little maintenance except for
periodic painting if desired. When applied and maintained properly, stucco
will last the lifetime of the structure as its inherent cement content is
nearly impervious to deterioration, excluding potential damage from
earthquakes or severe foundation settlement. Because of its workability
and a wide range of finishing options, stucco shapes the personality of a
structure, ranging from a high-tech look with symmetrical expansion joints
to a soft plaster-like finish giving warmth of a country cottage or the
patina of a classic Mediterranean villa.
Stucco, like any material, can be applied in numerous ways, hence
depending on who you talk to, you'll get as many opinions as real facts.
Traditionally, stucco is applied in a 3-coat fashion. The first coat,
called a scratch coat, is the thickest -- usually about 1/2". It
provides a solid wire-reinforced base on which to apply subsequent coats.
While the scratch coat is still wet, a notched trowel is used to engrave a
pattern of groves that look like giant scratches. This provides an added,
rough surface area for bonding of the next coat.
The second coat, the Brown coat, is generally 1/4" thick. Its
purpose is to provide added mass and thickness to the coating for
increased strength and water protection. Finally, a 1/8" thick finish
coat is applied to give the desired appearance such as smooth, floated,
Mediterranean knock-down, or skip troweled.
In an age of soaring construction costs nearing $150-$200 per square
foot in the San Francisco area, numerous techniques for cutting corners
have emerged, many of which show up even in multi-million dollar
residences I have examined in the most exclusive areas. One such technique
is called a 2-coat stucco process. It saves an entire step in the process,
costing less in labor in materials. In a 2-coat process, the first coat is
called the brown coat and the final coat is the finish coat. At first
glance, this technique may provide a finished appearance that's hard to
distinguish from a three coat job, but the overall thickness, crack
resistance, and longevity of the stucco will have been reduced. There's
almost always a price to pay for cutting corners. If you’re building a
house for yourself and pride yourself in doing things right, any competent
stucco contractor will tell you that a 3-coat job is the right way to do
it. Anything less is cutting corners. Even then, the savings may not be
that great, perhaps just a few thousand dollars on a typical 3,000 square
foot home.
After interviewing several stucco men, we learned a lot about the
tricks of the trade. Here's some of them, all of which have some effect on
the cost of the overall job.
Sub-base Sheathing
While stucco can be applied directly over studs using wire lath, more
commonly stucco is applied over plywood sheathing, particularly in
earthquake country where most of the outside walls are generally fully
covered with shearwall (plywood sheathing). In earthquake country where
shearwalls are part of the design code, minimum shearwall thickness is
typically 3/8". Because plywood is never quite the full stated
thickness, however, go with 1/2" plywood minimum. When using 2x4 or
2x6 stud framing, 1/2" plywood - coupled with 1/2" sheetrock
gives you a finished wall thickness width of roughly 4-1/2" or
6-1/2", respectively. This is ideal for standard wood window jambs
commonly quoted as 4-9/16" for 2x4 studs and 6-9/16" for 2x6
studs. This leaves a little margin for variations in 2x4 dimensions and
any thin mud coating you might apply to the sheetrock. For extra stability
for the stucco base, consider using 3/4" plywood, particularly if
it's over 2x6 framing on 24" centers. While the extra thickness is
overkill from a shearwall perspective, the 3/4" thickness makes an
exceptionally solid and stable base for stucco. Nails and staples
penetrate well into the wood to provide extra gripping power. Realize,
however, that by going with thicker shearwall, your window jambs will be
non-standard. Depending on your window type, this may not be an issue. In
fact, jamb extensions are easily applied at the manufacturer or by your
contractor. Heavier plywood, however, will add to cost. This generally
isn't necessary if your stucco installer is careful to anchor the lath
securely to stud locations as opposed to the spans between the studs.
Furthermore, insist for both shear protection and stucco stability that
any horizontal edges of the plywood sheathing have blocking on the
opposite side. Shearwall tests show a 2 to 1 improvement in shear holding
strength when all edges are nailed off compared to unsupported edges. This
also stabilizes the plywood against potential warping that could cause
cracking in the stucco.
Paper and Lath
The uniform building code requires a minimum of 2 layers of Type
"D" paper, designed for use as an underlayment for stucco. Some
people have used 15 lb. felt over a single layer of type "d"
paper. While this sounds good in theory, the asphalt saturation of the
felt makes it difficult for the wall to breathe. Therefore, moisture
emanating from inside the house will have a more difficult time escaping.
In cooler climates or poorly ventilated homes, this could lead to mold and
dryrot inside the wall cavity. Using an extra layer or two of type
"d" paper is a good compromise. It provides additional
protection against exterior moisture penetration, but still allows the
wall to breathe through the pores in the paper. Ask your stucco installer
to use copper staples which don't tend to rust like galvanized steel
staples. They cost more, but what's a few extra bucks for a first class
stucco job!
Good attention to detail is important when lathing a home. For example,
the paper should always be applied horizontally starting from the bottom
of the wall and working up your way up. Horizontal seams should overlap by
at least 4", although 6" provides a little more margin of
safety. Furthermore all windows and doors should be pre-flashed with a
double layer of Kraft-faced flashing paper. The doors and windows should
be well caulked with a continuous bead of 30-year silicone caulking
applied according to manufacturer's recommendations. Finally, the tops of
all windows and exterior door jambs should have a vinyl or primed
galvanized or copper sheet metal Z-bar flashing to ensure that moisture
does not tend to drip behind the window frame. These essential points
assure that any water or moisture that hits the paper has no chance of
dripping between the paper and the shearwall or through your windows and
doors, causing premature dry rot, water staining on the interior
sheetrock, or a damp haven for termites. Telltale signs of poor flashing
and caulking often show up as water stains, excessive moisture, or even
mold on the interior areas of sheetrock near the window jamb or frame.
For added moisture protection in areas that will be continuously
exposed to the elements (such as stucco-finished exterior balcony wall,
etc., or in contact with cement flatwork such as entryway porches, steps,
patio slabs, etc.), a relatively new product called Bituthene can provide
years of worry-free protection and waterproofing when applied in
accordance to the manufacturer's instructions.
Once the paper is applied, stucco lath or wire netting is applied as a
reinforcement for the scratch coat of stucco. A variety of types exist,
but always insist on 17-gauge wire. Other wires exists that are thinner,
and therefore have less reinforcement value. We used Jansen wire netting
on our job.
To save labor, much stucco netting is called "self furring,"
meaning that slight kinks in the netting ensure that the wire mesh is not
flush against the wall. The goal is ensure that the reinforcing material
is well imbedded into the stucco, ensuring optimal strength. This netting
can be stapled to the wall using a pneumatic staple gun. Unfortunately,
even with self-furring netting, the tendency is for the reinforcement to
stay squashed against the wall. To avoid this problem, always insist on
the use of furring nails placed on studs at 6" o.c. to provide plenty
of imbedment room for the scratch coat. This takes more labor but makes
for a superior base coat that will be less susceptible to cracking. Using
furring nails might add a few hundred dollars to a base bid. Many lathers
use nails as standard procedure. Be sure to ask what your bid includes.
For a small additional cost, you can specify added reinforcement at the
corners of all window and door openings. The right-angle formed at any
corner tends to be a weak point in the stucco, in which hairline stress
fractures commonly occur, shooting off diagonally from each corner. The
reinforcement is mere a 12" x 12" piece of fine wire lath with a
6"x6" piece notched out for the window frame. When placed on the
corner of each opening, localized reinforcement of the stucco is provided,
minimizing the chance of stress fractures around the corner, although some
are likely to appear as a matter of course. This trick is rarely included
as part of a standard stucco bid as the building code does not require it.
However, given that you want things done right, always specify this extra
step to ensure a minimum of unsightly cracks. Our stucco man did this for
an extra $200 for our 3,000 square foot home.
Decorative Trim and Detailing for Stucco
Perhaps one of the most exciting developments in exterior detailing is
the recent introduction of modified expanded polystyrene (EPS) foam
shapes. With total architectural flexibility, foam shapes of unlimited
design complexity are cost-effectively manufactured by a select group of
specialty firms in the West Coast. Using a computer-aided entry system, it’s
a simple matter to custom design crown molding, cornices, corbels,
columns, rosettes, window sills and trim, and other decorative detailing
once reserved for grand villas. During the manufacturing process, a
computer-controlled laser cuts the prescribed contour into the foam,
yielding a highly uniform product. Objects such as crown molding, for
example, are typically manufactured in 8-foot lengths. To speed
installation, some manufacturers also provide cutting and mitering
services, such as pre-made inside and outside corners and returns. Because
of their light weight, foam shapes are readily installed by one or two
craftsmen who secure the shapes into place with screws, nails, or a
special bonding agent.
Once the raw foam has been shaped and precut to required sizes, some
manufacturers offer an additional service which includes the placement of
a fiberglass mesh reinforcing tape such as that used in the application of
sheetrock is placed over the entire surface area of the foam. A thin brown
coat of cementitious material is spread evenly over the entire surface,
providing a protective and durable bond coat ready for final texturing
after installation. Seams and joints between adjacent foam pieces (such as
in crown molding used in soffits) are spliced with additional fiberglass
mesh tape prior to the application of the final finish coat. Depending on
the architectural style of the project, the color and finish texture can
match or contrast with the walls. One elegant scheme is to have a
hand-troweled smooth wall texture with a float-finish on the molding and
window sills, for example. This provides not only some aesthetic
diversity, but helps to break the monotony of a monotonic finish.
Because of their lightweight nature, foam shapes are growing rapidly in
popularity. Unlike wood, modified expanded polystyrene does not shrink or
expand noticeably with changes in temperature or moisture levels. Because
of their extreme stability and virtual imperviousness to deterioration,
foam shapes are being used increasingly as a substitute for wood. The
biggest drawback of EPS shapes is their resistance to impact damage.
However, when used in decorative applications not subject to physical
abuse, EPS shapes have a number of clear advantages that make them an
excellent new architectural tool to enhance the beauty and customized look
of your home. Unless otherwise specified, EPS shapes are generally made
with a 1-lb per cubic foot density. With this type of material, a 10%
deformation occurs at approximately 15 psi, while EPS made from 2-lb per
cubic foot density material has nearly double the compressive strength.
Stability is assured to temperatures as high as 167 degrees Fahrenheit
under continuous exposure conditions. Therefore, even in the Southwest
where temperatures can soar to 120 degrees and beyond, foam shapes will
stand the test of time.
As with any building materials, prices for foam shapes can vary
radically depending on the supplier, the size and complexity, the finish,
and the number of lineal feet ordered. I suggest getting bids from several
vendors before committing to one, as prices can vary more than 3 to 1 for
the same order. Furthermore, depending on the proximity of the
manufacturer to the job site, the cost of shipping alone can be
staggering. The foam shapes are sent via UPS or other carrier in the same
class as delicate china. That's because special care is required to handle
the sometimes large shapes which could be easily damaged or crushed during
shipment. Shipping charges of several hundred dollars are not uncommon for
an order containing five or six hundred lineal feet of lightweight foam.
For a basis of comparison, the price per foot of a custom ordered crown
molding (approximately 4.5 by 8.5 inches) was about $1.12/foot in raw cut
form, or nearly $4.00/foot with a brown coat applied. Additional charges
for precut corners, returns, and special miters can add another five or
ten percent to the total job price. We spent roughly $3,600 for slightly
over 400 feet of crown molding, 150 feet of a bellyband detail, and precut
window sills for 29 unique windows. The price of installation varies
according to your contractor, however can range from $1.00/foot on up,
depending on the size and ease/difficulty of installation. The company
that fabricated our foam shapes (Concept Designs of San Jose, California)
liked our crown molding detail so much they've decided to add it to their
catalog of standard shapes. Standard shapes have the advantage that there
is no design required and availability may be faster. Custom shapes,
however, can be designed for little or no additional fee, provided you
give a careful sketch and fully dimensioned diagram of your desired shape.
Foam shapes should be applied after the brown coat has been applied but
before the final coat is applied. Attention to detail, such as corner
alignment and straightness are critical to achieve a uniform, professional
installation. Because of slight variations in the brown coat thickness, a
red chalk line should be snapped horizontally along the wall to assure
cosmetic alignment of the pieces. Where seams occur between adjacent foam
strips, fiberglass mesh is applied to provide local reinforcement and good
bonding. A special bonding paste is applied to the seam and should dry
overnight before applying the finish coat texture.
The use of architectural foam shapes is by no means a requirement for a
good looking stucco job. But if you really want to add that special touch
of class to your home, try foam. You'll be glad you did it!
A more durable, but less flexible alternative to foam are rolled wire
shapes, such as 1" x 4" window trim. The wire shapes are nailed
in place during the lathing phase, and they become part of the stucco
itself. Sometimes reinforcing corners are used to provide extra strength.
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