Stucco

Decoration made with stucco.

Wall detail enriched with stucco.

The stucco is a fine-grained paste composed of slaked lime (usually greasy air lime), pulverized marble, plaster, natural pigments, etc., which hardens by chemical reaction when it comes into contact with contact the calcium hydroxide of lime with carbon dioxide (CO₂) [Ca(OH)₂ + CO₂ → CaCO₃ + H₂O] and is mainly used for plastering walls and ceilings.

Stucco can be treated in many ways, including modeling and carving to obtain ornamental forms, polishing to give it an appearance similar to marble, and polychrome painting for decorative purposes.

Another form of stucco is that made with plaster, animal glues and pigments; It is known as marble stucco due to its similarity in aesthetics, touch and shine to these natural stones.

The term stucco comes from the Italian stucco; It is a form of finishing or decoration of walls and ceilings, interior or exterior, based on paints and different types of mortar that allows obtaining different textures. Given its versatility, it adapts to any type of construction or period. In addition to its decorative function, it reinforces the wall and makes it waterproof, allowing natural transpiration.

The most famous stucco is Venetian, also called "lustro veneciano." It is a coating that was invented in Venice (Italy) at the beginning of the 15th century. Its finish shows a flat, smooth and shiny wall like polished marble, with different shades of colour, of great beauty.

Historical usage

Stuco dedicated to Antonio de Nebrija (1875).

During the Italian Renaissance, stucco was once again used as an architectural complement, along with painting, following the fashion originated by archaeological discoveries. A large number of techniques were perfected, which later spread throughout Europe. White stucco was widely used on church walls, sometimes to paint figures of angels. Raphael and other artists of the time used colored stucco friezes to decorate palaces and pavilions. Among the most relevant are the reliefs by Francesco Primaticcio (1533–1565) for the castle of Fontainebleau, near Paris.

This material reached its most splendid heights during the 17th and 18th centuries. Both the Baroque and the Rococo decorated their interiors with stucco, especially in Bavaria and Austria, where pilgrimage palaces and churches featured polychrome stucco in an infinite number of shapes—specular motifs, paired columns, and elaborate altars. Stucco also played an important role in architectural decoration in England, but in a less fanciful and exuberant way than in the Rococo; It reaches its climax with the architect Robert Adam, who used it for his exquisite wall and ceiling ornamentation, in neoclassical style. After Neoclassicism and except for certain Art Nouveau examples, the use of stucco declined in its artistic application.

Sculptural and architectural use

Baroque decorations of the main ship of the Basilica of the Monastery of Jasna Góra, 1693-1695

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 stucco reliefs from the Egyptian, Minoan and Etruscan periods have been preserved. In Mesopotamian and ancient Persian art there was a long tradition of figurative and ornamental internal stucco relief, which was continued in Islamic art, for example in Abbasid Samarra, now using geometric and vegetal ornaments. When the arabesque reached its full maturity, carved stucco continued to be a very common medium for decoration and calligraphic inscriptions. Indian architecture used stucco as a material for sculpture in an architectural context. It is rare in the field.

In Roman art of the late Republic and early Empire, stucco was widely used to decorate vaults. Although marble was the preferred sculptural medium in most cases, stucco was better for use in vaulting because it was lighter and better conformed to the curvature of the ceiling. [Baroque and Rococo architecture makes extensive use of stucco. We can find examples in churches and palaces, where stucco is used above all to provide a smooth and decorative transition from walls to ceiling, decorating and giving measure to the ceiling surfaces. Stucco is part of the art of belcomposto, the baroque concept that integrates the three classical arts, architecture, sculpture and painting.

Greco-Buddhist art in modern Afghanistan and northern Pakistan used stucco extensively in monasteries and temples for monumental three-dimensional sculpture, as well as reliefs. These were usually carved from a rough model on a frame and then painted. Similar techniques are used for the life-size statues that decorate the gopuram of Hindu temples in modern South Asia.

Since stucco can be used for both decoration and figurative representation, it makes an ideal transitive link between architectural details and wall paintings, such as trompe-l'œil ceilings. typically baroque, as in the work of the Wessobrunner School. Here, the actual architecture of the church is visually prolonged into a celestial architecture with a representation of Christ, the Virgin Mary or the Last Judgment in the center. Stucco is used to form a semi-plastic extension of the real architecture that blends with the painted architecture.

Bridges Music Hall in Claremont, California (1915), an example of stucco-plated reinforced concrete structure

Due to its "aristocratic" look, the baroque-looking stucco decoration was frequently used in upper-class apartments of the 19th century XIX and early XX.

Starting in the 1920s, stucco, especially in its neo-Renaissance and neo-Baroque embodiment, became increasingly unpopular with modern architects in some countries, leading not only to new buildings without stucco, but also to a widespread movement to remove stucco from existing homes.

Stucco was still used in the 1950s in molded forms to decorate the joints between walls and ceilings inside houses. It was usually painted the same color as the ceiling and used in designs where picture molding or rat molding was used.

Composition

Rock stucco used as an outside lining in a house on the west coast of Canada. The quartz, stone and coloured glass chips measure approximately 3-6 mm (1/8" - 1/4").

Within traditional stucco, the mortars are made up of lime, marble sand and natural pigments, which are usually varnished with wax or white spirit. It can also be made up of plaster, resins and natural glues.

The difference in nomenclature between stucco, plaster, and mortar is based more on use than composition. Until the latter part of the 19th century, it was common for plaster, which was used inside a building, and stucco, which was used on the exterior, were composed of the same primary materials: lime and sand (which are also used in the mortar). Animal fiber or vegetable fibers were often added to give it greater strength. In the late 19th century, Portland cement was added more frequently in an attempt to improve the durability of stucco. At the same time, the traditional lime plasters were replaced by plaster ones.

Traditional stucco is made of lime, sand, and water. Modern stucco is made of Portland cement, sand, and water. Lime is added to increase the permeability and workability of modern stucco. Additives such as acrylics and fiberglass are sometimes 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 much difficulty. The lime itself is usually white; the color comes from the aggregate or any added pigment. Lime stucco has the property of being self-healing to a limited degree due to the slight water solubility of lime (which in solution can settle into cracks, where it solidifies). Portland cement stucco is very hard and brittle and can easily crack if the base to which it is applied is not stable. Its color was normally gray, the innate color of most Portland cements, but white Portland cement is also used. Today, stucco manufacturers offer a very wide range of colors that can be fully mixed into the finish coat. Other materials, such as stone and broken glass, are sometimes "dusted" over the finish coat before drying, and the final product is commonly known as "rock dash", "pebble dash", or also as roughcast if the stones are incorporated directly into the stucco, used mainly from the early 20th century to the early XXI.

Application

About block

The surface is slightly moistened, and a layer of 2 to 4 mm is applied covering the entire area with a smooth trowel. The application is allowed to dry for 12 hours and a second layer of no more than 3 mm is applied to give the final finish.

On a thin surface of cement or plaster

The stucco is applied with a smooth trowel covering the entire surface with a layer of no more than 4 mm. Once drying has begun, it can be given texture.

Stucco repair

Causes of deterioration

Damaged stucco that has begun to get rid of its masonry substrate.

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 the problems become visible, as the damage will only get worse over time. Cracks can form in the stucco due to building settlement or direct damage to the exterior cladding. Once water gets through the siding, either through an opening in the stucco itself or from below its surface, the brittle stucco can begin to buckle and crumble. Wood is a common structural material often used as a substrate under stucco. It can absorb moisture from or below grade level and direct 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 problems is especially problematic. Stucco can delaminate from the damp wood below, and as the wood rots, the stucco can begin to deteriorate and separate from the wood and the building. Damage to the stucco itself leads to increased moisture infiltration that aggravates the deterioration of the finish, as well as the substrate. Downspouts, gutters, flashing, and other means of directing water away from the building will prevent damage from getting worse. Without proper guttering, water can splash onto stuccoed surfaces, staining and accelerating the deterioration of the finish. [Screen grading around the building may also be necessary to redirect moisture away from the structure and foundation.

Preparation and Repair

Depending on the extent of damage to the finish, varying degrees of repair may be accomplished. Small cracks can be sealed with an additional coat of finish or even just a coat of paint. Modern caulking materials are not the ideal means of repair. The choice to patch or completely repair a stuccoed surface depends on the texture of the topcoat. Repairs, especially large ones, made to a smooth finished surface will be more noticeable and refinishing the entire surface with a fresh coat of finish may be more appropriate. Conversely, it may be easier to hide repair patches on a textured surface and a complete refinish 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 must be removed, as it has failed. Removal of compromised materials can extend to wood lath or other substrates that may also have been damaged, although it may be preferable to install new lath over the damaged lath. Care must be taken with this approach, as it can be especially critical when authenticity is a concern in a historic building. In these cases, replacing the damaged battens is often considered more appropriate than installing a new mesh. All surfaces must be cleaned to remove paint, oil, or plant growth. Stone or brick mortar joints can be scored to a depth of 5/8" to allow the correct adhesion of the new stucco. New stucco patches should not overlap old stucco.

To obtain a clean repair, the area to be patched should be squashed with a tope joint, using a cold chin, an axe, a diamond leaf saw, or a masonry drill. Sometimes it may be preferable to leave the area to patch irregularly, which can lead to a less striking patch. The proper preparation of the area to patch requires very sharp tools, and an extreme caution on the part of the plaster to not break the keys of the surrounding good stucco by "overcoupling" by removing the deteriorated stucco.

Diagram showing the use of metal mesh as a substrate for an external Portland cement application.

Application of new stucco should not include metal lath when repairing lime stucco over a masonry surface. The new stucco repair must adequately adhere to the masonry substrate without lath. The introduction of metal mesh can accelerate the deterioration of both the masonry and the stucco finish, since the slightest moisture will cause the metal mesh to oxidize, which expands when it oxidizes. This can lead to the detachment of not only the new stucco, but also the masonry itself.

After thoroughly moistening the masonry or the wooden board, the first striped layer should be applied to the masonry substrate, or to the wooden or metal slate, in a thickness corresponding to the original if it exists, or generally around ¹♪₄′′ a ³♪₈. The scraping layer should be scratched or scratched on the cross with a comb to provide a key to holding the second layer. Usually, each layer takes between 24 and 72 hours, and more if it is cold, to heal before the following can be applied. The second layer should have about the same thickness as the first, and the total thickness of the first two layers should not generally exceed some ⁵♪₈′′. This second layer or leveling should be removed using a wooden floater with a nail that stands out to provide a key to the final or finishing layer. The finishing layer, of approximately ¹♪₄′′ thick, it is applied after the previous layer has initially fried. If this is not feasible, the base layer should be thoroughly moistened when the finish layer is applied later. The finishing layer should be worked to match the texture of the original stucco.