Appendix I: Conservation
Deterioration of Materials The occurrence of decay is not isolated but almost always part of a more complex process that involves physical and chemical environmental factors, and the structure and design of the building. One should also keep in mind that economical, legal and political aspects are just as important. However, the purpose of this section is to provide a general description of deterioration seen in frequently used building materials in the Harlem River Area. Ferrous Metals Metal corrosion occurs whenever a metallic surface oxidizes. Corrosion gone far enough has an effect on the structural and protective properties of a metal building component. Also the secondary effects can be just as serious, for example rusting iron and steel can expand ten times its size, and when this occurs within a structure the generated forces often cause damage on adjacent materials. In the Harlem River Area damages related to corroding steel can be observed in window casements where it instigates rust jacking of the glazing, and in lintels and sills, where it shatters the adjacent brickwork. Another example is rusting structural steel in columns and beams, causing cracks in the surrounding masonry walls. Rust derives from moisture, and in many cases water infiltration from failing roofs or gutters sets off these processes, which once initiated can accelerate rapidly and lead to further deterioration. Generally these situations can be avoided with continual maintenance. Once they have occurred the source of moisture must be eliminated. After the extent of damages has been determined the metal and masonry should be repaired or replaced. Brick, Stone and Masonry Brick is the most commonly used façade material in all surveyed sectors the study area. Masonry is primarily used as a secondary material, whereas stone is employed in details and ornaments. The properties of brick and masonry types vary greatly, as does their susceptibility to deterioration. Airborne particles from environmental pollution penetrate porous stone with rainwater, where subflorescence can then spall the material apart. Also pollution and dirt create hard crusts and stain the surface of the masonry. When cleaning masonry it is important to use a method that does not further harm the stone. Improper abrasive and chemical cleaning can damage the protecting surface of the masonry, exposing its structural body and increasing the rate of decay. Sulphur acids from burning of fossil fuels etch surfaces of brick and masonry and induce chemical reactions that deteriorate the stone. These processes leave the material more vulnerable to weathering. Water infiltration is also responsible for delamination of the brownstone (sandstone) commonly used as windowsills, stringcourses and decorations on buildings of the era. This occurs when water infiltrates between bedding planes, freezes, expands and separates the material. Water can also act to erode sedimentary stone, in extreme cases serving to direct moisture into the wall rather than away from it. Masonry load bearing walls absorb and evaporate water naturally. Provided the water is free of soluble salts this action is not harmful to the wall structure. However, the mortar used for pointing between masonry units contains lime, which is also soluble in water. As water moves through the masonry wall it has the effect over time of flushing the lime from the masonry joints. The correct repair for this is repointing with a similar mortar and implementation of a systematic maintenance program to ensure adequate bearing surface. There are many examples in the Harlem River Area where the necessity of making such a repair was resolved with a modern Portland Cement based mortar. This material is harder than the original masonry units, and due to differences in thermal expansion rates and moduli of elasticity the masonry may eventually crush, thereby exposing softer interior materials and inducing unit failure. Water infiltration followed by freeze-thaw cycling in areas where movement is constrained in plane, for example a corner, can lead to large vertical cracks, which can be of sufficient severity to impact structural integrity. This condition is exacerbated when a cosmetic repair using Portland cement is made creating a vertical section that will serve as a lever if moisture infiltration is not stopped and freeze-thaw cycling continues. Wood Historically and up to this day wood has been employed for all structural and ornamental elements of buildings. However, in the urban Harlem River Area, wood as a primary façade material can only be found in a few places, such as in Marble Hill. Worth noting is that the resided buildings on the map generally are wood framed and originally had wood façades. Like other materials, wood deterioration is in most cases associated with water. Wood expands and contracts with changing humidity, which is not harmful in itself, but a fitted wood piece may swell and be mechanically damaged. Also, if a piece of wood absorbs more water on one side than the other the differential expansion can cause it to warp. Microorganisms that feed from wood cause rot, and when the material is wetted without being able to properly dry those organisms will thrive and multiply. Wet or moist wood also attracts insects that nest or eat wood. Termites, carpenter ants and wood boring beetles can cause great damage to wood structures and features. The simple way to combat all of these deterioration processes is to keep the sources of moisture under control, and to allow the wood to dry out after being wet. In most cases regular maintenance is sufficient, but particularly exposed parts like windowsills need extra attention. Concrete The concentration of reinforced concrete buildings in the Harlem River Area are located in or near the Bronx Terminal Market. These were constructed between 1920-40, and all suffer from the effects of moisture infiltration. This takes the form of corroded reinforcing bars, which expand and force the concrete to spall off. The reinforcing bars, which were stable when embedded in the highly alkaline concrete environment, corrode more seriously as they are exposed to acidic moisture and precipitation. This pattern of deterioration, called carbonation, is enabled and further worsened by the local climate’s freeze thaw cycles. Although at this time deterioration on the Bronx Terminal Market buildings is mostly cosmetic with only some structural impact, intervention and regular maintenance is required to prevent total breakdown of the concrete. Seriously deteriorated structures may have their corroded members cut out and replaced with stainless steel reinforcements. Cracked or partially shattered concrete may be consolidated with injections of moisture-insensitive epoxy resins. The maintenance plan for the structures should include an awning or protective cover that sheds precipitation away from the concrete. Biological Growth Historic buildings constructed using lime mortar can become susceptible to damage from the roots of vegetation, such as ivy growth. Vegetation should be removed at regular intervals before the roots penetrate the masonry and cause spalling. The presence of moss on stone is an indication of a moist environment in which the stone does not have opportunity to dry. Moss in itself can harbor moisture and prevent stone from drying, which in turn can cause spalling and exfoliation. The acid run-off from moss and lichens gradually erodes all metals. There is a particular danger to lead work, but copper, zinc and iron are all at risk where these growths exist. Even though herbicides can be used to suppress biological growth, regular maintenance is usually enough to keep it under control. Graffiti Graffiti is visible on buildings throughout the Harlem River Area. Prompt removal of graffiti produces the most effective results and also discourages further occurrences in the immediate area. The first step to removing graffiti is to identify the staining material and the masonry substrate. The most common materials used are spray paint, brush applied paint, and permanent felt markers, but more everyday items such as lipstick or liquid shoe polish are used as well. Depending on the masonry substrate an appropriate cleaning agent, which could be a chemical solution or just detergent and water, should be used to remove the graffiti. Applying a poultice is the most preferred method of removing graffiti because it allows prolonged contact between the cleaning solution and the removal target, and draws the staining material out of the masonry without re-depositing it. Barrier coatings available on the market prevent graffiti from penetrating into the masonry and also facilitate graffiti removal. However, they may change the aesthetic appearance of the wall surface and even damage the masonry. Transparent treatments tend to alter the masonry surface color and add gloss. More importantly, the barrier may reduce water-vapor permeability and contribute to water-related deterioration. Ultimately, graffiti removal should be least harmful as possible to the masonry substrate, and an architectural conservator should be consulted when considering the application of a barrier coating.
The wood frame houses of Marble Hill are suffering from the widespread replacement of their historic wood siding. The reasons for this are varied and complex, but the end result is the same—the obscuring of the house’s architectural and material character. This discussion attempts to identify the causes, ramifications, and possible solutions to the problem. Effects of Replacement Siding on Historic Structures Before discussing the causes and possible solutions, it is important to understand the effects of replacement cladding such as aluminum or vinyl siding. The consequences are detrimental to the overall health of the house, and can sometimes be destructive to the original siding underneath. The following are only some of the possible effects:
In short, any benefits that replacement siding may provide are outweighed by the negative ramifications. Causes of Replacement Sidings on Historic Structures A host of factors positions the typical middle-class house owner of Marble Hill to easily make the choice to reside their house. A confluence of three primary influences drives the decision, and they can be characterized as financial, aesthetic, and commercial. It is important to state at the outset that the underlying condition in all three of these motivations is the uninformed or misinformed state of the owner.
The replacement siding industry is comprised of two separate entities—the manufacturers and the contractors. Furthermore, these businesses are networked in a chartered organization called The Vinyl Siding Institute, which is a business unit of The Plastic Industry, Inc. The VSI website states that that their purpose is to further the development and growth of the vinyl siding industry by: As in any profit generating business, high volume sales and contracts are the driving goals, and the replacement siding manufacturers are the primary catalysts of the booming industry. Many of the businesses have extensive sales channels, ranging from Home Depots to local hardware stores, and big budgets for marketing and advertising. The following is the main replacement siding pitch from Sears’ advertisement copy, which speaks for itself: Don’t spend your hard-earned money and precious time on the back-breaking chore of painting your house every few years. Trust your home to America’s largest home improvement company – Sears! Premium vinyl siding, eaves and overhangs from Sears give your home a freshly painted look, that lasts as long as you own it, making your home’s exterior virtually maintenance-free! Clearly, any average homeowner would be vulnerable to an industry machine of this magnitude. In addition to likening replacement siding to a modern miracle, the “experts” promote various other skewed messages. The claim is made that replacement siding with insulation backing improves the ‘thermal envelope’ of a structure. However, the materials themselves are not good insulators, and the majority of heat loss occurs through the roof. If there is a minimal amount of thermal improvement, it is simply because of the airspace created between the old and new cladding. Ultimately, the final decision in purchasing replacement siding comes down to money, and the fact of the matter is that Marble Hill is a middle class neighborhood. In light of expensive heating costs, it is understandable why homeowners are easily persuaded to purchase an item purported to be cheap, maintenance-free, long lasting, and thermally superior. As observed in the Sears quote above, wood siding suffers the image of being expensive and “back-breaking” to maintain. However, according to the National Park Service’s Preservation Brief #8, the average replacement siding job costs two or three times more than a paint job, even more if it is a sensitive job that retains much of the original trim. Considering that a good paint job lasts 8-10 years, the replacement siding must last 15-21 years to break even. If the property owner does not regularly conduct the yearly cleaning of the replacement siding (which they perceive to be a maintenance free system) it will surely result in deterioration and a soiled and dilapidated appearance. In the general building industry in the US, quality and longevity seems to be sacrificed for economy. Replacement siding is perceived as the inexpensive solution, but do property owners believe that it is an aesthetically pleasing solution as well? Or perhaps they think it is acceptable based on their misguided belief that it is the more economic method of maintaining their cladding. What is definite is the powerful influence of seeing replacement siding used ubiquitously in the community by their neighbors. A key reason why homeowners install replacement siding is to rejuvenate their home by giving it an instant “facelift” without the expense of remodeling. However, their desired results are fleeting. Replacement siding color fades and eventually loses its gloss. Furthermore, siding is a factory manufactured product and replacements can be difficult to find in the same color because of continual changes, unlike paints that can be matched and varied to the current hue for touch ups in between major paint jobs. Also, what the Vinyl Siding Institute does not proclaim is that aluminum siding is susceptible to dents and sometimes cracking. This is also true of vinyl siding, whose impact resistance lessens in low temperature weather, making it susceptible to cracking upon impact. Solutions to Combat Replacement Siding in Marble Hill To begin to reduce and reverse replacement siding in Marble Hill, it is essential to enlighten the community of the facts. These facts are:
These facts must be communicated with continued emphasis to the community to override the pro- replacement siding forces listed above. The most effective way of accomplishing this is to carry out grassroots style community outreach. Promoting awareness and providing follow-up advice and support in a positive and sensitive way is critical. One way of going about this is to have informational sessions that inspire property owners of Marble Hill’s history and significance, and stimulate interest in investing in the preservation of their neighborhood. Further steps might involve forming a neighborhood organization that would eventually empower the residents to steer their own path while receiving guidance from preservation professionals.
Buildings are intricate systems in which the functions of their separate parts are crucial to the overall performance. Windows are component of the climate shield of a building, and they simultaneously provide light and ventilation, and are important for the perception and usability of interior spaces. They are also a most apparent architectural element of the exterior, being crucial not only to the assessment, understanding and appreciation of an individual building, but also for the visual appearance and legibility of an area as a whole. A majority of the buildings in the Harlem River Area have had their original steel and wood windows replaced with aluminum or plastic. Buildings where the original windows still remain are threatened by the same degradation since they are often in poor condition. However, steel and wood can often be repaired and the unnecessary replacement of the original fabric is one aspect of the problem. The other aspect, which concerns necessary replacements, is material and design compatibility. In the case of the articulated wood architecture in Marble Hill, the art deco apartments buildings in Inwood and the industrial daylight factories in Mott Haven and the Bronx Terminal Market an informed and sensitive approach to window replacement could have a great positive effect on the entire neighborhoods, and for this purpose we would like to bring forward a few arguments. Aluminum and plastic do not have the combined strength and versatility of steel and wood, and it is apparent in the design of replacement windows. The result is boxier, less articulated forms and proportionally less glass surface. Glass surfaces are even further minimized when new frames are installed in old ones, which is common since there is no need to interfere with the wall when using this method. By the process a building is deprived of one of its most important architectural features, as are the spaces inside - where the reduced light transmission also necessitates compensation with artificial light. Aluminum and plastic windows are marketed as being maintenance-free. However, the other side of this is that they are not maintainable. As the windows age, wear and lose performance – which they inevitably do – they cannot be repaired or upgraded. This raises the question of what aluminum and plastic windows in turn shall be replaced with, when due in the foreseeable future. Alongside with being aesthetically compatible with the building, the basic demands of windows are durability, adequate light transmission, thermal properties and resistance to water penetration. Obviously they have to be economically feasible to buy, install and maintain. An aluminum or plastic window can be a suitable option in some instances, but evidently they are many times a misled, unfortunate and undesirable choice. When changing windows in buildings that where originally designed with wood or steel windows these materials should be the first explored. Window Replacement Procedures Before choosing a replacement window the following should be considered:
Glazing Another issue of replacement windows is the considerable visual difference between various types of glazing. Historic window glazing is usually thin, which permits a maximum of light transmission, but perhaps more important is the unevenness which gives the glass a live and permeable semblance. Many modern window glasses are extremely flat and reflective, making them appear opaque, which greatly impacts how a building or a streetscape is experienced. When replacing window glazing or choosing a new window, a glass with a minimum of glare should be used. If needed, different types of glass could be utilized on the interior and the exterior to achieve the best possible visual appearance in combination with other desirable properties. However, the matter of glazing is more difficult to address, since the market is geared towards technically advanced system solutions. It is worth noting that these systems are quite vulnerable. To give one example, gases with high thermal resistance are used between double-glazing. If the void is not completely sealed, which it might not be after transportation or a period of operation, the gas will escape and reduce the performance of the window. Retaining original windows Many times upgrading the existing wood and steel windows with simple measures like weather stripping, new sash locks, adding storm sashes and coating the glass are economically advantageous in the short and long term perspective. There are unfortunately no strong market forces willing to drive this thesis, but nevertheless there are companies that can repair existing steel and wood windows for a cost far less than that of replacement. Over the past decades more people have become more and more aware of the unsurpassed aesthetical qualities of original windows, and retaining them can have a positive effect on the property value. There are many ways to go about old windows but it is crucial to keep a holistic approach to the building, both visually and economically. Looking at Windows in a Broader Perspective When aiming for a sustainable society the time, energy and money invested in built structures should be regarded, but buildings should also be regarded as a cultural resource in the broadest sense. Buildings and built environments are an immense source of knowledge about the past and present. By preserving them, the information they are carriers of is made accessible and can be interpreted to create a greater understanding and sense of context. Recognizing and respecting the architectural integrity of buildings is not only an economical and aesthetical decision (but also a political statement).
Internet Resources Listed below are links to organizations that provide general information on historic preservation and more specific information on architectural conservation.
The Secretary of the Interior’s Standards The Secretary of the Interior’s Standards cover specific preservation treatments and approaches; their overriding philosophy is to maximize retention of historic features and materials while minimizing alterations. The intent of the Standards, which is to assure the long-term preservation of historic properties, can be summarized in general preservation principles that should be considered in planning work at any historic property. These preservation principles are:
Below is a condensed version of the principles found in the Secretary of the Interior’s Standards. These guidelines emphasize the relationship and differences among the four philosophical constructs.
National Park Service Preservation Briefs Such briefs are easy-to-read guides that are part of the National Park Service’s Preservation Technical Service. They describe methods of preserving, rehabilitating, and restoring historic buildings. Briefs 1-42 can be found online at http://www2.cr.nps.gov/tps/briefs/presbhom.htm. Preservation Briefs that are especially pertinent to the Harlem River Study Area include:
THE SECRETARY OF THE INTERIOR'S STANDARDS FOR REHABILITATION
CONSERVATION GLOSSARY Abrasive cleaning: Abrasive particles in a stream of pressurized air or water used to clean surfaces. Acid deposition: The accumulation of acidic materials, either atmospheric (dry) or water-borne (wet) on the surface of a material; usually oxides of nitrogen or sulfur. Accretion: The accumulation foreign material such as soot, salts, or other soiling mechanisms on the surface of a building element. Acid rain: Rain which is more acidic than pH 5.5. Alkaline: A compound which is above 5.5 on the pH scale. Most lime based materials are alkaline. Alligatoring: A pattern of cracking of an approximately rectangular grid. Usually caused by differential movement of a coating and substrate.. Alveolar deterioration: Formation of cavities in stone masonry surfaces caused by airborne abrasives. Usually cup-shaped. Anti-graffiti coating: A barrier coating applied (to masonry) to facilitate removal of graffiti. Can accelerate deterioration of the masonry. Arris: The exposed edges of bricks or dressed stone Ashlar: Stone masonry units which have been squared and surface-finished smooth. Basalt: A dense dark building stone composed of various compounds of augite, plagioclase, and magnetite. Bay: The spaces between window opening jambs on the facade of a building; a repetitive vertical subdivision of the facade. Bed: A horizontal surface of mortar on which a masonry unit rests; the upper horizontal surface of a masonry unit; the face of a stone unit which is parallel to the cleavage plane.Binder: The resinous material which attaches particles in a liquid or semi-liquid compound. Usually refers to material which binds pigment particles in paint. Bitumen: An asphaltic hydrocarbon, usually in semi-liquid state. Used for patching of other asphaltic materials. Bluestone: Bluish or blue-gray argillaceous sandstone, usually very fine grained and very durable. Used for lintels and sills. Bracciale: An ornamental plate on the facade of a building which holds a flag pole or other ornament. Brick veneer: A single wythe of brick on the surface of a building, supported by an independent frame or substrate. Bronze: A metal alloy composed of mostly copper, with smaller varying amounts of tin and other metals. Usually brown or reddish-brown. Brownstone: Any of a number of brown colored sandstones, used as facade material prominently in the 19th c. Calcareous cement: Any of a number of cements formed by mixing calcareous material(calcined limestone) argillaceous (clayey) material and siliceous (sand, quartz) materials. Cementitious coating: A stucco-like finish applied over the original material following initial construction. Occasionally applied as an alternative to repointing. Came: An “H” shaped metal strip which holds cut or stained glass elements within a window frame. Usually of lead but may be of copper. Cast iron: Iron formed by casting in molds, of high carbon content (up to 4%). Generally brittle with low tensile strength. Several varieties exist (gray, malleable, ductile) all with specific properties and uses. Cast stone: Any of a number of artificially produced “stones” composed of white portland cement and other aggregates, including marble dust, quartz, or other stones. Caustic Stripper: A paint stripper of alkaline composition, usually potassium or sodium hydroxide. Cavity wall: A masonry wall on which the inner and outer surfaces are separated by an air-space. Wall faces are joined by mechanical ties. Cement: Any material used to bind materials together following curing. Chalking: A whitish surface deposition on a painted surface caused by ultraviolet degradation of the paint binder or pigment. Chipping: Pieces of masonry separated from the unit at corners and joints, usually indicating mechanical damage. Composite repair: Material used for the surface repair of stone masonry consisting of cementitious material, aggregates, and pigment. Can be tooled to match original treatments. Conservator: An individual who practices, usually for insufficient salary, the art of conservation of materials, both artistic and architectural, in order to delay the natural process of decay. Copper: A corrosion resistant ductile element, frequently used as flashing material or for ornament. Has a service life expectancy of 60-80 years. Corrosion: The reaction of metals with other elements the result of which is the formation of various compounds. Water and oxygen are activating agents. Counterflashing (a.k.a. Cap flashing): Metal or other material on a wall surface which is located above and overlapping a vertical flashing (base flashing) below. Usually installed within a reglet in the wall. Cracking: Fissures in masonry units with various degrees of severity:
Cramp (a.k.a. a Dog): A metal strap which holds adjoining stone elements together, or stone facade material to rubble back-up. Crazing (a.k.a. Micro-fissuring): Formation of hairline cracks in the glaze of terra cotta. Can permit fungal growth, leading to enlarged cracking and greater water penetration into clay bisquit. Curtain wall: A non-load bearing wall supported by an independent structural framework. Deferred maintenance: Building maintenance which has been neglected for an extended period. Delamination: Peeling off of thin broad layers of stone. Related to the inherent physical structure of the material. Demolition by neglect: Destruction of a building by intentional or unintentional failure to perform maintenance functions. Desalinization: Removal of salts from a surface usually by application of poultices. Differential settlement: The downward movement of a section of a building caused by displacement usually at the foundation level. May be caused by uneven soil compaction. Disaggregation: Loss of aggregate in a stone usually as a result of dissolution of binder material. Displacement: The result of movement of a structural or cosmetic element from its proper position, due to settlement or shifting. Frequently marked by a complete separation of the element.Dry deposition: The deposit of dry pollutants on a surface; includes particulate pollutants. Dutchman: A repair consisting of installation of a piece of matching material within a mortised opening. Dutch metal: An alloy of copper and zinc which is used as an imitation gold leaf. Efflorescence: A powdery crystalline sulfate deposit, often white, which is the result of soluble salts leaching to the surface of a masonry element and deposited by evaporation. Enamel: A vitreous coating formed by firing a glazing material on the surface of a metal or ceramic substrate. Erosion: Wearing away of surface, edges, corners, or carved details by wind, windblown particles or water. Exfoliation: Surface deterioration caused by the expansion and contraction of trapped moisture or salts, other chemical action or weathering. Exposed aggregate: A finish formed on stucco or concrete by exposing the surface to an abrasion process (water, sand). Face bedded: Stone elements installed with the principle bedding (sediment) planes parallel to the exposed surface of the façade. Face: Installation of a veneer on the surface of a material. Ferrous: Any element formed of iron. Fire skin: The vitreous result of kiln firing of bricks or other terra cotta material. Flaking: Peeling, exfoliation, delamination or spalling in which detachment of small pieces from a larger stone occurs. Flashing: Sheet metal or other material used to prevent water from entering a building façade at joints or intersections of walls; historically of copper or lead. Freeze-thaw action: The result of internal pressure of freezing water within cavities in masonry elements, causing spalling or displacement. Galvanic corrosion: The action of an electric current generated by two different metals in close proximity with the presence of water, resulting in corrosion of the less noble metal. Graffito (pl. graffiti): A drawing or message scrawled on a structure, not intended by the original designer. Granite: Igneous stone composed of quartz with orthoclase feldspar, mica, hornblende and other minerals. A very dense and durable building stone. Gypsum deposits: An orange or black surface crust formed on limestone or marble by chemical reaction of calcite in the stone with air pollutants, usually sulfur dioxide. Hygroscopic: Material which is capable of absorbing moisture from the atmosphere Iron: A malleable elemental metal. Joint: The location at which two elements are joined. Lacuna (pl. Lacunae): A space or void on a facade where an element is missing due to deterioration or removal. Leaching deposits: Formation of hard crusts on masonry surfaces. Often caused by acid rain dissolving in the mortar joints. Limestone: A sedimentary rock formed principally of calcium carbonate from the shells of marine organisms. May also be formed with marl. Loss: Missing portion or whole of ornament or structure. (See Lacuna). Marble: A highly metamorphosed crystalline limestone, composed principally of calcium carbonate, and may also contain magnesium carbonate. Metal work: Building components composed of metal, may include cast, wrought, forged, repousse, rolled. Microclimate: The climate of a specific small area. Mill scale: A thin layer of ferric oxide left as a result of the hot rolling process on steel. Monel: Trade name for a 20th-century nickel-copper alloy and includes other metals which is silver-colored. Monitor: Periodic inspection over an extended period of time of a particular condition. Noble: Notation for a metal which is less or more prone to corrosion when in contact with another. More noble metals are less likely to corrode. Nondestructive testing: Testing of the condition or quality of a material by a means which does not damage or alter the sample. Generally performed using electronic means. Oolite (oolitic limestone): A coarse grained limestone composed of calcium carbonate cemented with other materials including sand and clay. Open joints: Describes joints between masonry units which have lost mortar. The condition can lead to water infiltration and instability. Organic damage: Vegetation or animal activity disrupts a building's structure or ornament. Also includes insect infestation and extensive bird droppings.Ossature: The frame of a building, the structural support. Overglaze: A secondary glaze applied to terra-cotta elements after the initial firing. Oxidation: Deterioration of metal by chemical reaction to weathering, moisture, chemicals, or agents in the environment, sometimes affecting overlying masonry. Oxide jacking: Breaking of masonry caused by expansion of encased or adjacent corroded metal, usually iron oxide. Pack rusting: Early indications of oxide jacking, usually consisting of only expanded iron oxide. Parging: An application of rough coat stucco to a masonry surface, generally for damp proofing. Passive iron: Iron which has been “passivated”, heat or chemically treated to increase resistance to corrosion. Patching: Inappropriate materials used to patch missing or cracked elements of a structure. Also includes anti-graffiti coatings. May accelerate problems. Patina: Brown or green corrosive product on the surface of bronze or copper elements which accumulates over time naturally. Artificially produced coloration on metals to replicate aged appearance. Peeling: Detachment of material (paint, parging, etc.) from the surface of a building, usually a result of water infiltration. pH: Measurement of the acidity or alkalinity of a substance. Example: a pH of 0 means very acidic, and a pH of 14 means very alkaline. Pitting: The development of small cavities in masonry surface caused by natural weathering erosion of harsh cleaning methods. Occurs in concrete due to improper mixing.Polyester: Synthetic resins of polymer compounds. Used with reinforcement to replicate ornament. Portland cement: A hydraulic cement composed of calcium carbonate, calcium silicates and aluminates, named for its resemblance to Portland stone. First patented in 1824. Precast: Common term for material composed of concrete which is cast in molds before being applied to a building. May be structural or ornamental pieces. Pressed brick: Bricks manufactured using a process of hydraulic pressure to form bricks which creates a very dense, smooth, and very uniform surface. Quarry bed: Stone laid with the bedding planes parallel to those of its natural state. Reglet: A continuous cut or slot in masonry generally used to anchor flashing edges. Rotting: Term describing wood which is suffering from biological (fungal) attack. Disintegration in wooden elements or structures. Rust: Iron oxide. Sandstone: Stone composed primarily of quartz grains in a matrix with silica, iron or other oxides, and calcium carbonate. Settlement: A structural condition identified by displacement of elements, cracks, or uneven elements. Sheet metal: Ductile metal which has been rolled to a uniform thickness, generally between 10-30 gauge, for stamping or forming. Shelf angle: A leg of an angle which projects horizontally from the structure of a building to support masonry or terra-cotta veneer elements. Silicone: Siloxane polymer resins (alternating silicon and oxygen atoms), which are chemically inert. Used to seal masonry elements. Slate: Fine grained argillaceous stone which splits easily at bedding planes. Soiling: Light, moderate or heavy deposits of dust, dirt, soot, generally deposited by electrostatic action. Spalling: Uneven chipping or flaking. Occurs in stone, brick and terra cotta from pressure of salts and freeze-thaw cycle as well as improper laying, repointing or cleaning. Also caused by water infiltration, which rusts metal anchors and causes increased uneven pressure on the masonry. Staining: Blemishes or residue deposits on masonry surface caused by material which has penetrated the surface of a material. Steel: High strength metal composed of iron with low carbon content. Often mixed with other metals for specific property alterations. Structural clay tile: Extruded clay units, including terra-cotta fired for use as masonry units. May include facing tiles, bearing and non-bearing clay tiles. Structural glass: Large glass panels produced for use as wall finishes (Example: Vitrolite). Sugaring: Loss of aggregate or friable condition in marble due to deterioration of cementing matrix. Surface induration: Hardening of the outer surface of stone masonry due to deposition of salts, with accompanying loss of stability of stone behind the outer surface. Terne: Sheet steel or tin which has been dipped in a led-zinc alloy, used on metal roofs and cornices. Terra-cotta: Fired ceramic clay, glazed or not, used for building elements. When applied as tile referred to as faience. Tessera (pl: tesserae): Individual mosaic tile.Tin: A malleable elemental metal, corrosion resistant, used for sheet application on buildings and as ornament back-up. Tooling: Finishing of stone masonry in which tool marks are visible in a pattern. Uneven settlement: Major structural problem. Identified by crooked facade, lintels, etc. Veneer: A thin layer of material applied to a structural substrate. Verdigris: Light green corrosion deposition, usually copper carbonate, on the surface of copper based metals. Wrought iron: Iron with a low carbon content which has been worked or “drawn” to align atoms into a microscopic “grain”. Used for decorative and structural elements. Wythe: A single layer of thickness of masonry elements in a wall. Zinc: An elemental metal with diamagnetic properties and a fibrous structure. Used for sheet metal applications, as well as galvanizing materials. Exposed zinc surfaces for a protective coating of zinc carbonate, a whitish powder. |