Historic Preservation - Technical Procedures

Preservation Briefs: 22 The Preservation And Repair Of Historic Stucco
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Preservation Briefs 22, National Park Service, Pad
Lath & Plaster
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Preservation Briefs: 22 The Preservation And Repair Of Historic Stucco
Last Modified:



The link that immediately follows connects to the latest version of the National Park Service Preservation Brief 22:




Anne Grimmer

This standard includes the bulk of information contained in the
original Preservation Brief developed by the National Park Service.
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The term "stucco" is used here 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.  Therefore, this Brief
has been prepared to provide background information on the nature
and components of traditional stucco, as well as offer guidance on
proper maintenance and repairs.  The Brief will outline the
requirements for stucco repair, and, when necessary, replacement.
Although several stucco mixes representative of different periods
are provided here for reference, this Brief does not include
specifications for carrying out repair projects.  Each project is
unique, with its own set of problems that require individual


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 limebased, 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
used 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, halftimbering,
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.


Stucco is primarily used on residential buildings and relatively
small-scale commercial structures.  Some of the earliest stucco
buildings in the United States include examples of the Federal,
Greek and Gothic Revival styles of the eighteenth and the
nineteenth centuries that emulated European architectural fashions.
Benjamin Henry Latrobe, appointed by Thomas Jefferson as Surveyor
of Public Buildings of the United States in 1803, was responsible
for the design of a number of important stucco buildings, including
St. John's Church (1816), in Washington, D.C.   Nearly half a
century later, Andrew Jackson Downing also advocated the use of
stucco in his influential book The Architecture of Country Houses,
published in 1850.  In Downing's opinion, stucco was superior in
many respects to plain brick or stone because it was cheaper,
warmer and dryer, and could be "agreeably" tinted.  As a result of
his advice, stuccoed Italianate style urban and suburban villas
proliferated in many parts of the country during the third quarter
of the nineteenth century.


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 1930's and 1940's, 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
1920's, 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.


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 rubble stone, 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


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 1820's.  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

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

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
glue size (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 some 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.


Stucco is applied directly, without lath, to masonry substrates
such as brick, stone, concrete or hollow tile.  On wood structures,
however, 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

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 1820's, 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.


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 rough-cast 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.



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.


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 limebased 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.


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 cut-off dates, as
stuccoing practices varied among individual plasterers, and from
region to region.  Some plasterers began using portland cement in
the 1880's, 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


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 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

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.

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

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 cross-hatched 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 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.


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 Stucco
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 an 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 approximated using sand, natural or
mineral pigments, or a combination of these.  Obtaining such a
match will require testing and comparing the color of 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.


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 an historic masonry specialist.


Last Reviewed 2012-09-10