stucco
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Stucco or render is a
construction Construction is a general term meaning the art and science to form Physical object, objects, systems, or organizations,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Pre ...
material made of aggregates, a binder, and water. Stucco is applied wet and hardens to a very dense solid. It is used as a decorative coating for walls and ceilings, exterior walls, and as a sculptural and artistic material in architecture. Stucco can be applied on construction materials such as
metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts Electrical resistivity and conductivity, el ...

metal
,
expanded metal lath
expanded metal lath
,
concrete Interior of the Pantheon dome, seen from beneath. The concrete for the coffered dome was laid on moulds, mounted on temporary scaffolding. Concrete is a composite material A composite material (also called a composition material or shorte ...
,
cinder block A concrete masonry unit (CMU) is a standard size rectangular block used in building construction. CMUs are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them. Those ...
, or clay
brick A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a block composed of dried clay, but is now also used informally to denote other chemically cured const ...

brick
and
adobe Adobe (; ) is a building material made from earth and organic materials. is Spanish for ' mudbrick', but in some English-speaking regions of Spanish heritage the term is used to refer to any kind of earthen construction. Most adobe buildin ...
for decorative and structural purposes. In English, "stucco" sometimes refers to a coating for the outside of a building and "
plaster Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English "plaster" usually means a material used for the interiors of buildings, while "rend ...
" to a coating for interiors; as described below, however, the materials themselves often have little to no differences. Other European languages, notably including Italian, do not have the same distinction; ''stucco'' means ''plaster'' in Italian and serves for both.


Composition

The basic composition of stucco is cement, sand, and water. The difference in nomenclature between stucco,
plaster Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English "plaster" usually means a material used for the interiors of buildings, while "rend ...
, and
mortar Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps between blocks and bind them together * Mortar and pestle, a tool pair used to crush or grind * Mortar, Bihar, a village in ...
is based more on use than composition. Until the latter part of the nineteenth century, it was common that plaster, which was used inside a building, and stucco, which was used outside, would consist of the same primary materials:
lime Lime refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany * Austra ...
and
sand Sand is a granular Granularity (also called graininess), the condition of existing in granules or grains A grain is a small, hard, dry seed A seed is an embryonic plant enclosed in a protective outer covering. The formation of th ...

sand
(which are also used in mortar).
Animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, ...
or plant fibers were often added for additional strength. In the latter nineteenth century,
Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in th ...

Portland cement
was added with increasing frequency in an attempt to improve the durability of stucco. At the same time, traditional
lime plaster Lime plaster is a type of plaster composed of sand, water, and lime, usually non-hydraulic hydrated lime (also known as slaked lime, high calcium lime or air lime). Ancient lime plaster often contained horse hair for reinforcement and pozzolanic ...

lime plaster
s were being replaced by
gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard/ sidewalk chalk, and drywal ...

gypsum
plaster. Traditional stucco is made of lime, sand, and water. Modern stucco is made of
Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in th ...

Portland cement
, sand, and water. Lime is added to increase the permeability and workability of modern stucco. Sometimes additives such as acrylics and glass fibers are added to improve the structural properties of the stucco. This is usually done with what is considered a one-coat stucco system, as opposed to the traditional three-coat method. Lime stucco is a relatively hard material that can be broken or chipped by hand without too much difficulty. The lime itself is usually white; color comes from the aggregate or any added
pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compound , CH4; is among the simplest organic compou ...
s. Lime stucco has the property of being self-healing to a limited degree because of the slight water
solubility In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atom ...

solubility
of lime (which in solution can be deposited in cracks, where it solidifies). Portland cement stucco is very hard and brittle and can easily crack if the base on which it is applied is not stable. Typically its color was gray, from the innate color of most Portland cement, but white Portland cement is also used. Today's stucco manufacturers offer a very wide range of colors that can be mixed integrally in the finish coat. Other materials such as stone and glass chips are sometimes "dashed" onto the finish coat before drying, with the finished product commonly known as "rock dash", "pebble dash", or also as
roughcast Pebbledashing Roughcast or pebbledash is a coarse plaster Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English "plaster" usually means ...
if the stones are incorporated directly into the stucco, used mainly from the early 20th through the early 21st centuries.


Traditional stucco

As a building material, stucco is a durable, attractive, and weather-resistant wall covering. It was traditionally used as both an interior and exterior finish applied in one or two thin layers directly over a solid
masonry Masonry is the building of structures from individual units, which are often laid in and bound together by mortar Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps betwee ...

masonry
,
brick A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a block composed of dried clay, but is now also used informally to denote other chemically cured const ...

brick
, or stone surface. The finish coat usually contained an integral color and was typically textured for appearance. Then with the introduction and development of heavy timber and light wood-framed construction methods, stucco was adapted for this new use by adding a reinforcement lattice, or
lath Roof laths span across between the rafters and support the wood shingles.A lath or slat is a thin, narrow strip of straight-grain A grain is a small, hard, dry seed, with or without an attached husk, hull or fruit layer, harvested for human or ...

lath
, attached to and spanning between the structural supports and by increasing the thickness and number of layers of the total system. The lath added support for the wet plaster and tensile strength to the brittle, cured stucco; while the increased thickness and number of layers helped control cracking. The traditional application of stucco and lath occurs in three coats—the scratch coat, the brown coat and the finish coat. The two base coats of plaster are either hand-applied or machine sprayed. The finish coat can be troweled smooth, hand-textured,
floated
floated
to a sand finish or sprayed. Originally, the lath material was strips of wood installed horizontally on the wall, with spaces between, that would support the wet plaster until it cured. This
lath and plaster 250px, Lath seen from the back with brown plaster coat oozing through Lath and plaster is a building process used to finish mainly interior dividing walls and ceilings. It consists of narrow strips of wood (laths) which are nailed horizontally acr ...
technique became widely used. In exterior wall applications, the lath is installed over a weather-resistant
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous The viscosity of a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external ...
- impregnated
felt Felt is a textile material that is produced by matting, condensing and pressing fibers together. Felt can be made of natural fibers such as wool Wool is the textile fiber obtained from sheep and other animals, including Cashmere wool, ca ...
or
paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, Textile, rags, poaceae, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre ev ...

paper
sheet that protects the framing from the moisture that can pass through the porous stucco. Following
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a World war, global war that lasted from 1939 to 1945. It involved World War II by country, the vast majority of the world's countries—including all the great ...
, the introduction of metal wire
mesh A mesh is a barrier made of connected strands of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearan ...

mesh
, or netting, replaced the use of wood lath.
Galvanizing Galvanization or galvanizing (American and British English spelling differences, also spelled galvanisation or galvanising) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot- ...
the wire made it
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rare ...
resistant and suitable for exterior wall applications. At the beginning of the 21st century, this "traditional" method of wire mesh lath and three coats of exterior plaster was still widely used. In some parts of the United States with a warmer climate (like
California California is a U.S. state, state in the Western United States. With over 39.3million residents across a total area of approximately , it is the List of states and territories of the United States by population, most populous and the List of ...
,
Nevada Nevada (, ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Ne ...

Nevada
,
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak) is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ' ...
,
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Greater Albuque ...

New Mexico
and
Florida Florida is a U.S. state, state located in the Southeastern United States, Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia (U.S. state), Georg ...

Florida
), stucco is the predominant exterior for both residential and commercial construction. Stucco exterior (with wood frame interior) became a popular alternative in the southwestern United States during the 1970s, as the masonry labor costs for
adobe Adobe (; ) is a building material made from earth and organic materials. is Spanish for ' mudbrick', but in some English-speaking regions of Spanish heritage the term is used to refer to any kind of earthen construction. Most adobe buildin ...
rose. Stucco relief fragment MET DP123867.jpg, Fragment from a
Roman Roman or Romans usually refers to: *Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of ancient Rome *''Epistle to the Romans'', shortened to ''Romans'', a letter in ...

Roman
relief; c. 138–161 AD; height: 20.9 cm;
Metropolitan Museum of Art The Metropolitan Museum of Art of New York City New York City (NYC), often simply called New York, is the List of United States cities by population, most populous city in the United States. With an estimated 2019 population of 8,336,817 ...

Metropolitan Museum of Art
(New York City) Afghanistan, Gandhara, Hadda, late Kushan Period - Seated Buddha - 1967.39 - Cleveland Museum of Art.tif, Statue of seated
Buddha Gautama Buddha, popularly known as the Buddha (also known as Siddhattha Gotama or Siddhārtha Gautama or Buddha Shakyamuni), was an Śramaṇa, ascetic, a religious leader and teacher who lived in History of India#Iron Age (1500 – 200 BCE ...
; c. 300s; overall: 36.9 cm; from Hadda (
Afghanistan Afghanistan (; Pashto/Dari language, Dari: , Pashto: , Dari: ), officially the Islamic Republic of Afghanistan, is a landlocked country at the crossroads of Central Asia, Central and South Asia. Afghanistan is bordered by Pakistan to the eas ...
);
Cleveland Museum of Art The Cleveland Museum of Art (CMA) is an art museum An art museum is a building or space for the display of art, usually from the museum's own Collection (artwork), collection. It might be in public or private ownership and may be accessible to ...
(
Cleveland Cleveland ( ), officially the City of Cleveland, is a city in the United States, U.S. U.S. state, state of Ohio, and the county seat of Cuyahoga County, Ohio, Cuyahoga County. It is located along the southern shore of Lake Erie, across the U.S. ...

Cleveland
,
Ohio Ohio () is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Of the List of states and territories of the United States, fifty states, it is the List of U.S. states and territories by area, 34th-large ...

Ohio
, USA) Relief plaque with confronted ibexes, Iran, Sasanian period, 5th or 6th century AD, stucco originally with polychrome painting - Cincinnati Art Museum - DSC03952.JPG, Iranian relief plaque with confronted ibexes; 5th or 6th century AD (the Sasanian period); stucco originally with polychrome painting;
Cincinnati Art Museum The Cincinnati Art Museum is an art museum An art museum is a building or space for the display of art, usually from the museum's own Collection (artwork), collection. It might be in public or private ownership and may be accessible to all or ...
(Cincinnati, USA) Wall panel depicting Ix K'an Bolon (Lady Precious Nine), Maya, Pomona, Tabasco state, Late Classic period, c. 790 AD, limestone, stucco, paint - Dallas Museum of Art - DSC04642.jpg, Maya civilization, Maya wall panel depicting Ix K'an Bolon; circa 790 AD (Late Classic period); limestone, stucco and paint; from Pomona, Tabasco, Pomona (Tabasco, Mexico) Dallas Museum of Art (Dallas, Texas, USA)


Sculptural and architectural use

Stucco has also been used as a sculptural and artistic material. Stucco relief was used in the architectural decoration schemes of many ancient cultures. Examples of Ancient Egypt, Egyptian, Minoan civilization, Minoan, and Etruscan civilization, Etruscan stucco reliefs remain extant. In the art of Mesopotamia and ancient Persian art there was a widespread tradition of figurative and ornamental internal stucco reliefs, which continued into Islamic art, for example in Abbasid Samarra, now using geometrical and plant-based ornament. As the arabesque reached its full maturity, carved stucco remained a very common medium for decoration and calligraphic inscriptions. Architecture of India, Indian architecture used stucco as a material for sculpture in an architectural context. It is rare in the countryside. In Roman art of the late Republic and early Empire, stucco was used extensively for the decoration of vaults. Though marble was the preferred sculptural medium in most regards, stucco was better for use in vaults because it was lighter and better suited to adapt to the curvature of the ceiling. Baroque architecture, Baroque and Rococo architecture makes heavy use of stucco. Examples can be found in churches and palaces, where stucco is mostly used to provide a smooth, decorative transition from walls to ceiling, decorating and giving measure to ceiling surfaces. Stucco is an integral part of the art of belcomposto, the Baroque concept that integrates the three Art in ancient Greece, classic arts, architecture, sculpture, and painting. The Greco-Buddhist art of modern
Afghanistan Afghanistan (; Pashto/Dari language, Dari: , Pashto: , Dari: ), officially the Islamic Republic of Afghanistan, is a landlocked country at the crossroads of Central Asia, Central and South Asia. Afghanistan is bordered by Pakistan to the eas ...
and northern Pakistan made extensive use in monasteries and temples of stucco for three-dimensional monumental sculpture as well as reliefs. These were usually carved from a rough modelling over a framework and then painted. Similar techniques are used for the life-size statues decorating the gopurams of Hindu temples in modern South Asia. Since stucco can be used for decoration as well as for figurative representation, it provides an ideal transitive link from architectural details to wall paintings such as the typically Baroque ''trompe-l'œil'' ceilings, as in the work of the Wessobrunner School. Here, the real architecture of the church is visually extended into a heavenly architecture with a depiction of Christ, the Blessed Virgin Mary, Virgin Mary or the Last Judgment at the center. Stucco is used to form a semi-plastic extension of the real architecture that merges into the painted architecture. Because of its "Aristocracy (class), aristocratic" appearance, Baroque-looking stucco decoration was used frequently in upper-class apartments of the 19th and early 20th century. Beginning in the 1920s, stucco, especially in its Renaissance Revival architecture, Neo-Renaissance and Baroque Revival architecture, Neo-Baroque materialization, became increasingly unpopular with modern architects in some countries, resulting not only in new buildings without stucco but also in a widespread to remove the stucco from existing tenements. Stucco was still employed in the 1950s in molded forms for decorating the joints between walls and ceilings inside houses. It was generally painted the same colour as the ceiling and used in designs where a picture rail or rat rail was in use.


Modern stucco

Modern stucco is used as an exterior Plaster#Cement plaster, cement plaster wall covering. It is usually a mix of
sand Sand is a granular Granularity (also called graininess), the condition of existing in granules or grains A grain is a small, hard, dry seed A seed is an embryonic plant enclosed in a protective outer covering. The formation of th ...

sand
,
Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in th ...

Portland cement
,
lime Lime refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany * Austra ...
and water, but may also consist of a proprietary mix of additives including fibers and synthetic acrylics that add strength and flexibility. Modern synthetic stucco can be applied as one base layer and a finish layer, which is thinner and faster to apply, compared to the traditional application of three-coat stucco. Imitation stone stucco can also be produced using the traditional application, but with marble dust being added to the mixture. As with any cement-based material, stucco must be reinforced to resist movement cracking. Plastic or wire
mesh A mesh is a barrier made of connected strands of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearan ...

mesh
lath Roof laths span across between the rafters and support the wood shingles.A lath or slat is a thin, narrow strip of straight-grain A grain is a small, hard, dry seed, with or without an attached husk, hull or fruit layer, harvested for human or ...

lath
, attached with nails or screws to the structural framing, is embedded into the base coat to provide stiffening for the stucco. One method often used to help conceal the smaller surface cracks that may appear is the application of one of a variety of pre-mixed acrylic finishes. Flexible acrylic finishes have the ability to stretch and bridge over cracks, improving appearance and limiting the passage of moisture behind the stucco. Where stucco is to be applied to a structure of wood-framing or light-gauge steel framing, the framing is protected from moisture damage by applying a cement based primer, or a vapor-permeable, water-resistant weather barrier; typically an
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous The viscosity of a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external ...
-saturated Tar paper, paper or one of a variety of manufactured plastic-based sheets, known as "Housewrap, building wraps" or "stucco wraps". The properties of the weather barrier must not only protect the framing from rain and moisture, but at the same time allow the free passage of any water vapor generated inside the building to escape through the wall. A wide variety of stucco accessories, such as weep screeds, control and expansion joints, corner-aids and architectural reveals are sometimes also incorporated into the lath. Wire lath is used to give the plaster something to attach to and to add strength. Types include expanded-metal lath, woven-wire lath, and welded-wire lath. The first layer of plaster is called a "scratch coat", consisting of plastic cement and sand. A trowel is used to scratch the surface horizontally or in a crisscross pattern to provide a key for the second layer. A brush is not used because it will cause delamination. The first coat is allowed to dry (cure) before the second layer is applied. The next layer is called the "brown coat" or leveling coat. It also consists of sand, cement, and lime. It is leveled with tools called "darbies", "rods", and "feathereges", scraped smooth, and floated to provide a smooth, even surface onto which the finish coat is applied. It is then allowed to dry (cure) for 7–10 days minimum to allow "checking" (shrinkage) and cracking to take place. If applied during very dry weather, the layers of stucco are sprayed with water for one or more days to keep a level of moisture within the stucco while it cures, a process known as "moist curing." If the stucco dries too soon, the chemical hardening ("hydration") will be incomplete, resulting in a weaker and brittler stucco. The final, exterior layer is the "finish coat", of which there are two recommended types: # Acrylic Finish, an acrylic-based finish from thick. It can be applied in many ways and can be ordered in any color. # Color Coat, a colored sand, cement, and lime mixed finish typically thick. It is applied over the second coat (brown coat) and can be floated with water for a sandy finish or textured over with a trowel to create various styles of finishes. Premixed, bagged stucco is gaining in use and is available in coarse graded sand and finer graded sand for creating a variety of troweled finishes; it is available in a variety of colors.


Repairing historic stucco


Causes of deterioration

The repair of historic stucco should begin by identifying the cause of the damage to the stucco finish. Historically, the application of stucco was quite similar to the process of applying lime plaster. Repairs should be carried out as soon as problems become visible, as the damage will only become worse over time. Cracks may form in the stucco due to building settling or direct damage to the exterior coating. Once water is able to breach the coating, whether through an opening in the stucco itself or from beneath its surface, fragile stucco can begin to buckle and crumble. Wood is a common structural material that is often used as substrate beneath stucco. It can absorb moisture from at or below ground level and draw it away from the original source of the problem. Stucco can also be applied to masonry such as brick or stone, which can also be damaged by moisture infiltration. Rising damp from groundwater or drainage issues is especially problematic. The stucco can Delamination, delaminate from damp wood lath beneath and as the wood rots, the stucco may begin to deteriorate and separate from it and the building. Damage to the stucco itself leads to further moisture infiltration that exacerbates the deterioration of the finish as well as the substrate. Downspouts, gutters, flashing and other means of managing directing water away from the building will prevent damage from getting worse. Without proper guttering, water may splash up onto stuccoed surfaces, staining and accelerating the deterioration of the finish. Grade (slope), Grading of the soil around the building may also be necessary to redirect moisture away from the structure and foundation.


Preparation and repair

Depending on the extent of the damage to the finish, varying degrees of repairs may be carried out. Small hairline cracks may be sealed with an additional layer of finish coat or even simply a coat of paint. Modern caulking materials are not ideal mediums of repair. Making the choice to patch or completely repair a stuccoed surface depends on the texture of the finish coat. Repairs, especially numerous ones, made to a smoothly finished surface will be more noticeable and recovering the entire surface with a new layer of finish coat may be more appropriate. Conversely, it may be easier to conceal patches of repair work to a textured surface and complete refinishing may not be necessary. Preparation should begin with the removal of all damaged material in the area to be repaired. Any stucco that is loose should be removed as it has already failed. The removal of compromised materials may extend to wood lath or other substrates that may have also have been damaged, although it may be preferable to install new mesh over damaged lath. Care must be taken regarding this approach, as it may be especially critical when authenticity is of a concern regarding a historic building. In such cases, replacement of damaged lath is generally considered to be more appropriate than installing new mesh. All surfaces should be cleaned to remove paint, oil, or plant growth. Stone or brick mortar joints may be scored to a depth of 5/8" to allow for the proper adhesion of the new stucco. New stucco patches should not overlap old stucco.
To obtain a neat repair, the area to be patched should be squared-off with a butt joint, using a Chisel#Cold chisel, cold chisel, a hatchet, a Diamond blade, diamond blade saw, or a Drill bit#Masonry drill bits, 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.
The application of new stucco should not include wire mesh when lime stucco is being repaired on a masonry surface. The new stucco repair should bond to the masonry substrate appropriately without mesh. The introduction of wire mesh has the potential to hasten deterioration of both the masonry and the stucco finish as the slightest amount of moisture will lead to rust developing on the wire mesh, which expands as it rusts. This may lead to the spalling of not only the new stucco, but also of the masonry itself.
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 ″ to ″. 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 cure 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 ″. 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 ″ 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.


Additional considerations

Preparing for the repair process requires testing to determine the composition of the stucco that is to be repaired. Due to numerous factors, including regionally available materials and original workmanship, there is a variety of materials that may have been used for the original application of stucco. It must also be determined if the type of stucco used is lime-based or Portland cement-based. Of particular concern is the use of Portland cement, which is harder than previous methods used in stucco application. This material is not compatible with softer and more flexible lime cement that was used in the 18th and into the mid-19th centuries. Test sampling is critical to determine the best mixture, in terms of durability, compatibility, texture and color to use in the repair process. Test patches should be used to help make this determination. The same number of layers should be used in the repair as were used in the original stucco application. A professional plasterer or contractor familiar with the process of making repairs to historic stucco should carry out necessary repairs. Typically, a homeowner should not attempt to repair stucco finishes on their own. Further research that should be conducted prior to the commencement of repair includes determining the types of ingredients used in the original stucco so that the color and texture of the original material can be matched as closely as possible. In some cases, shells or pebbles were used in the stucco covering. Regionally sourced sand, for example, may have been used in the original application, but may no longer be readily available. In this way, stucco tended to be tinted directly, although sometimes it was painted after being applied. Additionally, the use of ingredients such as animal hair was popular in some regions. Care should be taken that repairs made include similar ingredients that are clean and free of oils. This is another reason for the use of test patches, to ensure that the repairs blend into the original building fabric as much as possible.


See also

* Cement render * Exterior insulation finishing system * Harl * Hy-Rib * Lath and plaster * Opus albarium * Pargeting * Plaster * Plasterwork * Polished plaster * Siding (construction), Siding * Tadelakt


References


Further reading

* * * * {{Authority control Building materials Plastering Wallcoverings