The stucco on
the early-19th century
Richardson-Owens-Thomas
House in Savannah,
Georgia, is a type of
natural cement.
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Stucco has been used since ancient
times. Still widely used throughout the
world, it is one of the most common of
traditional building materials. Up until
the late 1800's, stucco, like mortar,
was primarily lime-based, but the
popularization of portland cement
changed the composition of stucco, as
well as mortar, to a harder material.
Historically, the term "plaster" has
often been interchangeable with
"stucco"; the term is still favored by
many, particularly when referring to the
traditional lime-based coating. By the
nineteenth century "stucco," although
originally denoting fine interior
ornamental plasterwork, had gained wide
acceptance in the United States to
describe exterior plastering. "Render"
and "rendering" are also terms used to
describe stucco, especially in Great
Britain. Other historic treatments and
coatings related to stucco in that they
consist at least in part of a similarly
plastic or malleable material include:
parging and pargeting, wattle and daub,
"cob" or chalk mud, pise de terre,
rammed earth, briquete entre poteaux or
bousillage, half-timbering, and adobe.
All of these are regional variations on
traditional mixtures of mud, clay, lime,
chalk, cement, gravel or straw. Many are
still used today.
The stucco
finish on Arlington
House, Arlington,
Virginia, was marbleized
in the 1
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Revival
Styles Promote Use of Stucco
The introduction of the many revival
styles of architecture around the turn
of the twentieth century, combined with
the improvement and increased
availability of portland cement resulted
in a "craze" for stucco as a building
material in the United States. Beginning
about 1890 and gaining momentum into the
1930s and 1940s, stucco was associated
with certain historic architectural
styles, including: Prairie; Art Deco,
and Art Moderne; Spanish Colonial,
Mission, Pueblo, Mediterranean, English
Cotswold Cottage, and Tudor Revival
styles; as well as the ubiquitous
bungalow and "four-square" house. The
fad for Spanish Colonial Revival, and
other variations on this theme, was
especially important in furthering
stucco as a building material in the
United States during this period, since
stucco clearly looked like adobe.
Although stucco buildings were
especially prevalent in California, the
Southwest and Florida, ostensibly
because of their Spanish heritage, this
period also spawned stucco-coated,
revival-style buildings all over the
United States and Canada. The popularity
of stucco as a cheap, and readily
available material meant that by the
1920s, it was used for an increasing
variety of building types. Resort
hotels, apartment buildings, private
mansions and movie theaters, railroad
stations, and even gas stations and
tourist courts took advantage of the
"romance" of period styles, and adopted
the stucco construction that had become
synonymous with these styles.
The damage to
this stucco appears to
be caused by moisture
infiltration.
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A Practical Building Material
Stucco has traditionally been popular
for a variety of reasons. It was an
inexpensive material that could simulate
finely dressed stonework, especially
when "scored" or "lined" in the European
tradition. A stucco coating over a less
finished and less costly substrate such
as rubblestone, fieldstone, brick, log
or wood frame, gave the building the
appearance of being a more expensive and
important structure. As a
weather-repellent coating, stucco
protected the building from wind and
rain penetration, and also offered a
certain amount of fire protection. While
stucco was usually applied during
construction as part of the building
design, particularly over rubblestone or
fieldstone, in some instances it was
added later to protect the structure, or
when a rise in the owner's social status
demanded a comparable rise in his
standard of living.
Composition of Historic Stucco
Before the mid-to-late nineteenth
century, stucco consisted primarily of
hydrated or slaked lime, water and sand,
with straw or animal hair included as a
binder. Natural cements were frequently
used in stucco mixes after their
discovery in the United States during
the 1820s. Portland cement was first
manufactured in the United States in
1871, and it gradually replaced natural
cement. After about 1900, most stucco
was composed primarily of portland
cement, mixed with some lime. With the
addition of portland cement, stucco
became even more versatile and durable.
No longer used just as a coating for a
substantial material like masonry or
log, stucco could now be applied over
wood or metal lath attached to a light
wood frame. With this increased
strength, stucco ceased to be just a
veneer and became a more integral part
of the building structure.
Caulking is not
an appropriate method
for repairing cracks in
historic stucco.
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Today, gypsum, which is hydrated calcium
sulfate or sulfate of lime, has to a
great extent replaced lime Gypsum is
preferred because it hardens faster and
has less shrinkage than lime. Lime is
generally used only in the finish coat
in contemporary stucco work.
The composition of stucco depended on
local custom and available materials.
Stucco often contained substantial
amounts of mud or clay, marble or brick
dust, or even sawdust, and an array of
additives ranging from animal blood or
urine, to eggs, keratin or gluesize
(animal hooves and horns), varnish,
wheat paste, sugar, salt, sodium
silicate, alum, tallow, linseed oil,
beeswax, and wine, beer, or rye whiskey.
Waxes, fats and oils were included to
introduce water-repellent properties,
sugary materials reduced the amount of
water needed and slowed down the setting
time, and alcohol acted as an air
entrainer. All of these additives
contributed to the strength and
durability of the stucco.
The appearance of much stucco was
determined by the color of the sand--or
sometimes burnt clay--used in the mix,
but often stucco was also tinted with
natural pigments, or the surface
whitewashed or color-washed after
stuccoing was completed. Brick dust
could provide color, and other coloring
materials that were not affected by
lime, mostly mineral pigments, could be
added to the mix for the final finish
coat. Stucco was also marbled or
marbleized--stained to look like stone
by diluting oil of vitriol (sulfuric
acid) with water, and mixing this with a
yellow ochre, or another color. As the
twentieth century progressed,
manufactured or synthetic pigments were
added at the factory to some prepared
stucco mixes.
Methods of Application
Stucco is applied directly, without
lath, to masonry substrates such as
brick, stone, concrete or hollow tile.
But on wood structures, stucco, like its
interior counterpart plaster, must be
applied over lath in order to obtain an
adequate key to hold the stucco. Thus,
when applied over a log structure,
stucco is laid on horizontal wood lath
that has been nailed on vertical wood
furring strips attached to the logs. If
it is applied over a wood frame
structure, stucco may be applied to wood
or metal lath nailed directly to the
wood frame; it may also be placed on
lath that has been attached to furring
strips. The furring strips are
themselves laid over building paper
covering the wood sheathing.
The dry
materials must be mixed
thoroughly before adding
water to make the
stucco.
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Wood lath was gradually superseded by
expanded metal lath introduced in the
late-nineteenth and early-twentieth
century. When stuccoing over a stone or
brick substrate, it was customary to cut
back or rake out the mortar joints if
they were not already recessed by
natural weathering or erosion, and
sometimes the bricks themselves were
gouged to provide a key for the stucco.
This helped provide the necessary bond
for the stucco to remain attached to the
masonry, much like the key provided by
wood or metal lath on frame buildings.
Like interior wall plaster, stucco has
traditionally been applied as a
multiple-layer process, sometimes
consisting of two coats, but more
commonly as three. Whether applied
directly to a masonry substrate or onto
wood or metal lath, this consists of a
first "scratch" or "pricking-up" coat,
followed by a second scratch coat,
sometimes referred to as a "floating" or
"brown" coat, followed finally by the
"finishing" coat. Up until the
late-nineteenth century, the first and
the second coats were of much the same
composition, generally consisting of
lime, or natural cement, sand, perhaps
clay, and one or more of the additives
previously mentioned. Straw or animal
hair was usually added to the first coat
as a binder. The third, or finishing
coat, consisted primarily of a very fine
mesh grade of lime and sand, and
sometimes pigment. As already noted,
after the 1820s, natural cement was also
a common ingredient in stucco until it
was replaced by portland cement. Both
masonry and wood lath must be kept wet
or damp to ensure a good bond with the
stucco. Wetting these materials helps to
prevent them from pulling moisture out
of the stucco too rapidly, which results
in cracking, loss of bond, and generally
poor quality stuccowork.
Traditional Stucco Finishes
Until the early-twentieth century when a
variety of novelty finishes or textures
were introduced, the last coat of stucco
was commonly given a smooth, troweled
finish, and then scored or lined in
imitation of ashlar. The illusion of
masonry joints was sometimes enhanced by
a thin line of white lime putty,
graphite, or some other pigment. Some
nineteenth century buildings feature a
water table or raised foundation of
roughcast stucco that differentiates it
from the stucco surface above, which is
smooth and scored. Other novelty or
textured finishes associated with the
"period" or revival styles of the
early-twentieth century include: the
English cottage finish, adobe and
Spanish, pebble-dashed or dry-dash
surface, fan and sponge texture,
reticulated and vermiculated, roughcast
(or wet dash), and sgraffito.
Regular Maintenance
Although A. J. Downing alluded to
stuccoed houses in Pennsylvania that had
survived for over a century in
relatively good condition, historic
stucco is inherently not a particularly
permanent or long-lasting building
material. Regular maintenance is
required to keep it in good condition.
Unfortunately, many older or historic
buildings are not always accorded this
kind of care.
Because building owners knew stucco to
be a protective, but also somewhat
fragile coating, they employed a variety
of means to prolong its usefulness. The
most common treatment was to whitewash
stucco, often annually. The lime in the
whitewash offered protection and
stability and helped to harden the
stucco. Most importantly, it filled
hairline cracks before they could
develop into larger cracks and let in
moisture. To improve water repellency,
stucco buildings were also sometimes
coated with paraffin, another type of
wax, or other stucco-like coatings, such
as oil mastics.
Assessing Damage
Most stucco deterioration is the result
of water infiltration into the building
structure, either through the roof,
around chimneys, window and door
openings, or excessive ground water or
moisture penetrating through, or
splashing up from the foundation.
Potential causes of deterioration
include: ground settlement lintel and
door frame settlement, inadequate or
leaking gutters and downspouts,
intrusive vegetation, moisture migration
within walls due to interior
condensation and humidity, vapor drive
problems caused by furnace, bathroom and
kitchen vents, and rising damp resulting
from excessive ground water and poor
drainage around the foundation. Water
infiltration will cause wood lath to
rot, and metal lath and nails to rust,
which eventually will cause stucco to
lose its bond and pull away from its
substrate.
The deteriorated
surface of this catch
basin is being
re-stuccoed.
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After the cause of deterioration has
been identified, any necessary repairs
to the building should be made first
before repairing the stucco. Such work
is likely to include repairs designed to
keep excessive water away from the
stucco, such as roof, gutter, downspout
and flashing repairs, improving
drainage, and redirecting rainwater
runoff and splash-back away from the
building. Horizontal areas such as the
tops of parapet walls or chimneys are
particularly vulnerable to water
infiltration, and may require
modifications to their original design,
such as the addition of flashing to
correct the problem.
Previous repairs inexpertly carried out
may have caused additional
deterioration, particularly if executed
in portland cement, which tends to be
very rigid, and therefore incompatible
with early, mostly soft lime-based
stucco that is more "flexible."
Incompatible repairs, external vibration
caused by traffic or construction, or
building settlement can also result in
cracks which permit the entrance of
water and cause the stucco to fail.
Before beginning any stucco repair, an
assessment of the stucco should be
undertaken to determine the extent of
the damage, and how much must be
replaced or repaired. Testing should be
carried out systematically on all
elevations of the building to determine
the overall condition of the stucco.
Some areas in need of repair will be
clearly evidenced by missing sections of
stucco or stucco layers. Bulging or
cracked areas are obvious places to
begin. Unsound, punky or soft areas that
have lost their key will echo with a
hollow sound when tapped gently with a
wooden or acrylic hammer or mallet.
Identifying the Stucco Type
Analysis of the historic stucco will
provide useful information on its
primary ingredients and their
proportions, and will help to ensure
that the new replacement stucco will
duplicate the old in strength,
composition, color and texture as
closely as possible. However, unless
authentic, period restoration is
required, it may not be worthwhile, nor
in many instances possible, to attempt
to duplicate all of the ingredients
(particularly some of the additives), in
creating the new stucco mortar. Some
items are no longer available, and
others, notably sand and lime--the major
components of traditional stucco--have
changed radically over time. For
example, most sand used in contemporary
masonry work is manufactured sand,
because river sand, which was used
historically, is difficult to obtain
today in many parts of the country. The
physical and visual qualities of
manufactured sand versus river sand, are
quite different, and this affects the
way stucco works, as well as the way it
looks. The same is true of lime, which
is frequently replaced by gypsum in
modern stucco mixes. And even if
identification of all the items in the
historic stucco mix were possible, the
analysis would still not reveal how the
original stucco was mixed and applied.
There are, however, simple tests that
can be carried out on a small piece of
stucco to determine its basic makeup. A
dilute solution of hydrochloric
(muriatic) acid will dissolve lime-based
stucco, but not portland cement.
Although the use of portland cement
became common after 1900, there are no
precise cutoff dates, as stuccoing
practices varied among individual
plasterers, and from region to region.
Some plasterers began using portland
cement in the 1880s, but others may have
continued to favor lime stucco well into
the early twentieth century. While it is
safe to assume that a late-eighteenth or
early-nineteenth century stucco is
lime-based, late-nineteenth or
early-twentieth century stucco may be
based on either lime or portland cement.
Another important factor to take into
consideration is that an early
lime-stucco building is likely to have
been repaired many times over the
ensuing years, and it is probable that
at least some of these patches consist
of portland cement.
Planning the Repair
Once the extent of damage has been
determined, a number of repair options
may be considered. Small hairline cracks
usually are not serious and may be
sealed with a thin slurry coat
consisting of the finish coat
ingredients, or even with a coat of
paint or whitewash.
Commercially available caulking
compounds are not suitable materials for
patching hairline cracks. Because their
consistency and texture is unlike that
of stucco, they tend to weather
differently, and attract more dirt; as a
result, repairs made with caulking
compounds may be highly visible, and
unsightly. Larger cracks will have to be
cut out in preparation for more
extensive repair. Most stucco repairs
will require the skill and expertise of
a professional plasterer.
The stucco will
be applied to the wire
lath laid over the area
to be patched.
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In the interest of saving or preserving
as much as possible of the historic
stucco, patching rather than wholesale
replacement is preferable. When
repairing heavily textured surfaces, it
is not usually necessary to replace an
entire wall section, as the textured
finish, if well-executed, tends to
conceal patches, and helps them to blend
in with the existing stucco. However,
because of the nature of smooth-finished
stucco, patching a number of small areas
scattered over one elevation may not be
a successful repair approach unless the
stucco has been previously painted, or
is to be painted following the repair
work. On unpainted stucco such patches
are hard to conceal, because they may
not match exactly or blend in with the
rest of the historic stucco surface. For
this reason it is recommended, if
possible, that stucco repair be carried
out in a contained or well-defined area,
or if the stucco is scored, the repair
patch should be "squared-off" in such a
way as to follow existing scoring. In
some cases, especially in a highly
visible location, it may be preferable
to restucco an entire wall section or
feature. In this way, any differences
between the patched area and the
historic surface will not be so readily
apparent.
Repair of historic stucco generally
follows most of the same principles used
in plaster repair. First, all
deteriorated, severely cracked and loose
stucco should be removed down to the
lath (assuming that the lath is securely
attached to the substrate), or down to
the masonry if the stucco is directly
applied to a masonry substrate. A clean
surface is necessary to obtain a good
bond between the stucco and substrate.
The areas to be patched should be
cleaned of all debris with a bristle
brush, and all plant growth, dirt, loose
paint, oil or grease should be removed.
If necessary, brick or stone mortar
joints should then be raked out to a
depth of approximately 5/8" to ensure a
good bond between the substrate and the
new stucco.
To obtain a neat repair, the area to be
patched should be squared-off with a
butt joint, using a cold chisel, a
hatchet, a diamond blade saw, or a
masonry bit. Sometimes it may be
preferable to leave the area to be
patched in an irregular shape which may
result in a less conspicuous patch.
Proper preparation of the area to be
patched requires very sharp tools, and
extreme caution on the part of the
plasterer not to break keys of
surrounding good stucco by
"over-sounding" when removing
deteriorated stucco.
To ensure a firm bond, the new patch
must not overlap the old stucco. If the
stucco has lost its bond or key from
wood lath, or the lath has deteriorated
or come loose from the substrate, a
decision must be made whether to try to
reattach the old lath, to replace
deteriorated lath with new wood lath, or
to leave the historic wood lath in place
and supplement it with modern expanded
metal lath. Unless authenticity is
important, it is generally preferable
(and easier) to nail new metal lath over
the old wood lath to support the patch.
Metal lath that is no longer securely
fastened to the substrate may be removed
and replaced in kind, or left in place,
and supplemented with new wire lath.
When repairing lime-based stucco applied
directly to masonry, the new stucco
should be applied in the same manner,
directly onto the stone or brick. The
stucco will bond onto the masonry itself
without the addition of lath because of
the irregularities in the masonry or
those of its mortar joints, or because
its surface has been scratched, scored
or otherwise roughened to provide an
additional key. Cutting out the old
stucco at a diagonal angle may also help
secure the bond between the new and the
old stucco. For the most part it is not
advisable to insert metal lath when
restuccoing historic masonry in sound
condition, as it can hasten
deterioration of the repair work. Not
only will attaching the lath damage the
masonry, but the slightest moisture
penetration can cause metal lath to
rust. This will cause metal to expand,
eventually resulting in spalling of the
stucco, and possibly the masonry
substrate too.
The final finish
coat will be applied to
this scratch coat.
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If the area to be patched is properly
cleaned and prepared, a bonding agent is
usually not necessary. However, a
bonding agent may be useful when
repairing hairline cracks, or when
dealing with substrates that do not
offer a good bonding surface. These may
include dense stone or brick, previously
painted or stuccoed masonry, or spalling
brick substrates. A good mechanical bond
is always preferable to reliance on
bonding agents. Bonding agents should
not be used on a wall that is likely to
remain damp or where large amounts of
salts are present. Many bonding agents
do not survive well under such
conditions, and their use could
jeopardize the longevity of the stucco
repair.
A stucco mix compatible with the
historic stucco should be selected after
analyzing the existing stucco. It can be
adapted from a standard traditional mix
of the period, or based on one of the
mixes included here. Stucco consisting
mostly of portland cement generally will
not be physically compatible with the
softer, more flexible lime-rich historic
stuccos used throughout the eighteenth
and much of the nineteenth centuries.
The differing expansion and contraction
rates of lime stucco and portland cement
stucco will normally cause the stucco to
crack. Choosing a stucco mix that is
durable and compatible with the historic
stucco on the building is likely to
involve considerable trial and error,
and probably will require a number of
test samples, and even more if it is
necessary to match the color. It is best
to let the stucco test samples weather
as long as possible--ideally one year,
or at least through a change of seasons,
in order to study the durability of the
mix and its compatibility with the
existing stucco, as well as the
weathering of the tint if the building
will not be painted and color match is
an important factor.
If the test samples are not executed on
the building, they should be placed next
to the stucco remaining on the building
to compare the color, texture and
composition of the samples with the
original. The number and thickness of
stucco coats used in the repair should
also match the original.
After thoroughly dampening the masonry
or wood lath, the first, scratch coat
should be applied to the masonry
substrate, or wood or metal lath, in a
thickness that corresponds to the
original if extant, or generally about
1/4" to 3/8". The scratch coat should be
scratched or crosshatched with a comb to
provide a key to hold the second coat.
It usually takes 24-72 hours, and longer
in cold weather, for each coat to dry
before the next coat can be applied. The
second coat should be about the same
thickness as the first, and the total
thickness of the first two coats should
generally not exceed about 5/8". This
second or leveling coat should be
roughened using a wood float with a nail
protruding to provide a key for the
final or finish coat. The finish coat,
about 1/4" thick, is applied after the
previous coat has initially set. If this
is not feasible, the base coat should be
thoroughly dampened when the finish coat
is applied later. The finish coat should
be worked to match the texture of the
original stucco.
Colors and Tints for Historic Stucco
Repair
The new addition
on the right is stucco
scored to imitate the
limestone of the
historic building on the
left.
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The color of most early stucco was
supplied by the aggregate included in
the mix--usually the sand. Sometimes
natural pigments were added to the mix,
and eighteenth and nineteenth-century
scored stucco was often marbleized or
painted in imitation of marble or
granite. Stucco was also frequently
coated with whitewash or a colorwash.
This tradition later evolved into the
use of paint, its popularity depending
on the vagaries of fashion as much as a
means of concealing repairs. Because
most of the early colors were derived
from nature, the resultant stucco tints
tended to ne mostly earth-toned. This
was true until the advent of brightly
colored stucco in the early decades of
the twentieth century. This was the
so-called "Jazz Plaster" developed by
O.A. Malone, the "man who put color into
California," and who founded the
California Stone Products Corporation in
1927. California Stucco was
revolutionary for its time as the first
stucco/plaster to contain colored
pigment in its pre-packaged factory mix.
When patching or repairing a historic
stucco surface known to have been
tinted, it may be possible to determine
through visual or microscopic analysis
whether the source of the coloring is
sand, cement, or pigment. Although some
pigments or aggregates used
traditionally may no longer be
available, a sufficiently close
color-match can generally be
approximately using sand, natural or
mineral pigments, or a combination of
these. Obtaining such a match will
require testing and comparing the color
of the dried test samples with the
original. Successfully combining
pigments in the dry stucco mix prepared
for the finish coat requires
considerable skill. The amount of
pigment must be carefully measured for
each batch of stucco. Overworking the
mix can make the pigment separate from
the lime. Changing the amount of water
added to the mix, or using water to
apply the tinted finish coat, will also
affect the color of the stucco when it
dries.
Generally, the color obtained by
hand-mixing these ingredients will
provide a sufficiently close match to
cover an entire wall or an area distinct
enough from the rest of the structure
that the color differences will not be
obvious. However, it may not work for
small patches conspicuously located on a
primary elevation, where color
differences will be especially
noticeable. In these instances, it may
be necessary to conceal the repairs by
painting the entire patched elevation,
or even the whole building.
Many stucco buildings have been painted
over the years and will require
repainting after the stucco repairs have
been made. Limewash or cement-based
paint, latex paint, or oil-based paint
are appropriate coatings for stucco
buildings. The most important factor to
consider when repainting a previously
painted or coated surface is that the
new paint be compatible with any coating
already on the surface. In preparation
for repainting, all loose or peeling
paint or other coating material not
firmly adhered to the stucco must be
removed by hand-scraping or natural
bristle brushes. The surface should then
be cleaned.
Cement-based paints, most of which today
contain some portland cement and are
really a type of limewash, have
traditionally been used on stucco
buildings. The ingredients were easily
obtainable. Furthermore, the lime in
such paints actually bonded or joined
with the stucco and provided a very
durable coating. In many regions,
whitewash was applied annually during
spring cleaning. Modern, commercially
available premixed masonry and
mineral-based paints may also be used on
historic stucco buildings.
If the structure must be painted for the
first time to conceal repairs, almost
any of these coatings may be acceptable
depending on the situation. Latex paint,
for example, may be applied to slightly
damp walls or where there is an excess
of moisture, but latex paint will not
stick to chalky or powdery areas.
Oil-based, or alkyd paints must be
applied only to dry walls; new stucco
must cure up to a year before it can be
painted with oil-based paint.
Contemporary Stucco Products
There are many contemporary stucco
products on the market today. Many of
them are not compatible, either
physically or visually, with historic
stucco buildings. Such products should
be considered for use only after
consulting with a historic masonry
specialist. However, some of these
prepackaged tinted stucco coatings may
be suitable for use on stucco buildings
dating from the late-nineteenth or
early-twentieth century, as long as the
color and texture are appropriate for
the period and style of the building.
While some masonry contractors may, as a
matter of course, suggest that a
water-repellent coating be applied after
repairing old stucco, in most cases this
should not be necessary, since color
washes and paints serve the same
purpose, and stucco itself is a
protective coating.
Cleaning Historic Stucco Surfaces
Historic stucco buildings often exhibit
multiple layers of paint or limewash.
Although some stucco surfaces may be
cleaned by water washing, the relative
success of this procedure depends on two
factors: the surface texture of the
stucco, and the type of dirt to be
removed. If simply removing airborne
dirt, smooth unpainted stucco, and
heavily-textured painted stucco may
sometimes be cleaned using a
low-pressure water wash, supplemented by
scrubbing with soft natural bristle
brushes, and possibly non-ionic
detergents. Organic plant material, such
as algae and mold, and metallic stains
may be removed from stucco using
poultices and appropriate solvents.
Although these same methods may be
employed to clean unpainted roughcast,
pebble-dash, or any stucco surface
featuring exposed aggregate, due to the
surface irregularities, it may be
difficult to remove dirt, without also
removing portions of the decorative
textured surface. Difficulty in cleaning
these surfaces may explain why so many
of these textured surfaces have been
painted.
When Total Replacement is Necessary
Complete replacement of the historic
stucco with new stucco of either a
traditional or modern mix will probably
be necessary only in cases of extreme
deterioration-- that is, a loss of bond
on over 40-50 percent of the stucco
surface. Another reason for total
removal might be that the physical and
visual integrity of the historic stucco
has been so compromised by prior
incompatible and ill-conceived repairs
that patching would not be successful.
When stucco no longer exists on a
building there is more flexibility in
choosing a suitable mix for the
replacement. Since compatibility of old
and new stucco will not be an issue, the
most important factors to consider are
durability, color, texture and finish.
Depending on the construction and
substrate of the building, in some
instances it may be acceptable to use a
relatively strong cement-based stucco
mortar. This is certainly true for many
late-nineteenth and early-twentieth
century buildings, and may even be
appropriate to use on some stone
substrates even if the original mortar
would have been weaker, as long as the
historic visual qualities noted above
have been replicated. Generally, the
best principle to follow for a masonry
building is that the stucco mix, whether
for repair or replacement of historic
stucco, should be somewhat weaker than
the masonry to which it is to be applied
in order not to damage the substrate.
General Guidance for Historic Stucco
Repair
A skilled professional plasterer will be
familiar with the properties of
materials involved in stucco repair and
will be able to avoid some of the
pitfalls that would hinder someone less
experienced. General suggestions for
successful stucco repair parallel those
involving restoration and repair of
historic mortar or plaster. In addition,
the following principles are important
to remember:
-
Mix only as much stucco as can be
used in one and one-half to two
hours. This will depend on the
weather (mortar will harden faster
under hot and dry, or sunny
conditions); and experience is
likely to be the best guidance. Any
remaining mortar should be
discarded; it should not be
retempered.
-
Stucco mortar should not be
over-mixed. (Hand mix for 10-15
minutes after adding water, or
machine mix for 3-4 minutes after
all ingredients are in mixer.)
Over-mixing can cause crazing and
discoloration, especially in tinted
mortars. Over-mixing will also tend
to make the mortar set too fast,
which will result in cracking and
poor bonding or keying to the lath
or masonry substrate.
-
Wood lath or a masonry substrate,
but not metal lath, must be
thoroughly wetted before applying
stucco patches so that it does not
draw moisture out of the stucco too
rapidly. To a certain extent,
bonding agents also serve this same
purpose. Wetting the substrate helps
retard drying.
-
To prevent cracking, it is
imperative that stucco not dry too
fast. Therefore, the area to be
stuccoed should be shaded, or even
covered if possible, particularly in
hot weather. It is also a good idea
in hot weather to keep the newly
stuccoed area damp, at approximately
90 per cent humidity, for a period
of 48 to 72 hours.
-
Stucco repairs, like most other
exterior masonry work, should not be
undertaken in cold weather (below 40
degrees Fahrenheit, and preferably
warmer), or if there is danger of
frost.
Historic Stucco Textures
Most of the oldest stucco in the U.S.
dating prior to the late-nineteenth
century, will generally have a smooth,
troweled finish (sometimes called a sand
or float finish), possibly scored to
resemble ashlar masonry units. Scoring
may be incised to simulate masonry
joints, the scored lines may be
emphasized by black or white penciling,
or the lines may simply be drawn or
painted on the surface of the stucco. In
some regions, at least as early as the
first decades of the nineteenth century,
it was not uncommon to use a roughcast
finish on the foundation or base of an
otherwise smooth-surfaced building.
Roughcast was also used as an overall
stucco finish for some outbuildings, and
other less important types of
structures.
This stucco
house has a rough cast
finish.
|
A wide variety of decorative surface
textures may be found on revival style
stucco buildings, particularly
residential architecture. These styles
evolved in the late-nineteenth century
and peaked in popularity in the early
decades of the twentieth century. Frank
Lloyd Wright favored a smooth finish
stucco, which was imitated on much of
the Prairie style architecture inspired
by his work. Some of the more
picturesque surface textures include:
English Cottage or English Cotswold
finish; sponge finish; fan texture;
adobe finish; and Spanish or Italian
finish. Many of these finishes and
countless other regional and
personalized variations on them are
still in use.
The most common early-twentieth century
stucco finishes are often found on
bungalow-style houses, and include:
spatter or spatterdash (sometimes called
roughcast, harling, or wetdash), and
pebble-dash or drydash. The spatterdash
finish is applied by throwing the stucco
mortar against the wall using a whisk
broom or a stiff fiber brush, and it
requires considerable skill on the part
of the plasterer to achieve a
consistently rough wall surface. The
mortar used to obtain this texture is
usually composed simply of a regular
sand, lime, and cement mortar, although
it may sometimes contain small pebbles
or crushed stone aggregate, which
replaces one-half the normal sand
content. The pebble-dash or drydash
finish is accomplished manually by the
plasterer throwing or "dashing" dry
pebbles (about 1/8" to 1/4" in size),
onto a coat of stucco freshly applied by
another plasterer. The pebbles must be
thrown at the wall with a scoop with
sufficient force and skill that they
will stick to the stuccoed wall. A more
even or uniform surface can be achieved
by patting the stones down with a wooden
float. This finish may also be created
using a texturing machine.
Stucco on historic buildings is
especially vulnerable not only to the
wear of time and exposure to the
elements, but also at the hands of
well-intentioned "restorers," who may
want to remove stucco from eighteenth
and nineteenth century structures, to
expose what they believe to be the
original or more "historic" brick, stone
or log underneath. Historic stucco is a
character-defining feature and should be
considered an important historic
building material, significant in its
own right. While many eighteenth and
nineteenth century buildings were
stuccoed at the time of construction,
others were stuccoed later for reasons
of fashion or practicality. As such, it
is likely that this stucco has acquired
significance over time, as part of the
history and evolution of a building.
Thus, even later, non-historic stucco
should be retained in most instances;
and similar logic dictates that new
stucco should not be applied to a
historic building that was not stuccoed
previously. When repairing historic
stucco, the new stucco should duplicate
the old as closely as possible in
strength, composition, color and
texture.
