Columbus Ohio Home Inspection Pros ®
Stucco Homes
The Preservation and Repair of Historic Stucco
The term "stucco" is used to describe a type of exterior plaster
applied as a two-or-three part coating directly onto masonry, or
applied over wood or metal lath to a log or wood frame
structure. Stucco is found in many forms on historic structures
throughout the United States. It is so common, in fact, that it
frequently goes unnoticed, and is often disguised or used to
imitate another material. Historic stucco is also sometimes
incorrectly viewed as a sacrificial coating, and consequently
removed to reveal stone, brick or logs that historically were
never intended to be exposed. Age and lack of maintenance hasten
the deterioration of many historic stucco buildings. Like most
historic building materials, stucco is at the mercy of the
elements, and even though it is a protective coating, it is
particularly susceptible to water damage.
Stucco is a material of deceptive simplicity: in most cases its
repair should not be undertaken by a property owner unfamiliar
with the art of plastering. Successful stucco repair requires
the skill and experience of a professional plasterer. Although
several stucco mixes are representative of different periods are
provided here for reference Each project is unique, with its own
set of problems that require individual solutions
Historical Background
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
plaster work, 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.
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.
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.
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.
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 stucco work.
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.
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.
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 re-stucco 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 re-stuccoing 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.
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 stucco
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 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 be 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. Lime
wash 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 lime wash, 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 re-tempered.
- 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 stucco 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 stucco 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.
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 dry dash 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
stucco 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 stucco at
the time of construction, others were stucco 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 stucco previously. When
repairing historic stucco, the new stucco should duplicate the
old as closely as possible in strength, composition, color and
texture.
Contents
PATCH
Independent Home Inspections, LLC
Serving Columbus and Central Ohio
Rick A. Harrington
13514 Falmouth Ave
Pickerington, Ohio 43147
(614) 565-4962
(614) 768-1190 fax
Home Inspections
Thermal Imaging (Infrared)
Central Ohio Certified Home Inspections
