Cover Image

PAPERBACK
$97.25



View/Hide Left Panel
Click for next page ( 212


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 211
Diagnosis of Nonstructural Problems in Histonc Masonry Buildings BAIRD M. SMITH This paper explores the deterioration of stone and brick in buildings and mon- uments caused by defects in building design or by materials that have proven nonfunctional or of lower than expected performance and durability. For in- st~nce, frequent problems occur from the corrosion of metal anchorage devices, improper design of stone details precluding proper drainage of rainwater, and the unexpected ramifications of newly installed air conditioning or the intro- duction of thermal insulation. A variety of cases are identified to aid in the proper diagnosis of problems and determination of treatments. The paper does not deal with deterioration from primary sources, such as airborne pollutants, freeze/thaw cycling, or thermal stressing, but rather with deterioration re- sulting from improper construction practices, weak design details, or the use of materials that have since proven em satisfactory. This report is different from most of the others in that it does not deal with deterioration associated with airborne pollution, rain, and other moisture-related problems, but with deterioration from secondary causes. For example, the report explores causes such as poor craftsmanship or construction practice, or materials and budding systems that simply have not performed as well as elected. Thus, topics such as freeze/ thaw, acid attack, and so on are not mentioned; the focus is on building- Baird M. Smith is Historical Architect, Heritage Conservation and Recreation Service, U.S. Department of the Interior, Washington, D. C. 211

OCR for page 211
212 CONSERVATION OF HISTORIC STONE BUILDINGS practices, with the emphasis on buildings and techniques used from the late nineteenth century to the present. The approach here is to look at the basic physical elements of a building, then to describe the evolution of the building technologies affecting those elements. Thus, after presenting some overriding con- ditions, the following building elements are discussed: Walls Top of Walls Window Openings Base of Walls In each case, emphasis is placed on an evaluation of actual building practices to determine causes for common problems. Proper identifi- cation and understanding of the earlier building systems is indispens- able when attempting to diagnose current problems and prescribe treat- ments. This report should aid architects, engineers, and builders in the proper diagnosis of such problems. Throughout this report, some rather extreme cases of building failure are cited. This is not meant to overdramatize the topic, but rather to present a reasonably accurate assessment of the potential for modern building failures resulting from poor original building practices. One must remember that from 1880 to 1940 there was tremendous competition among builders, architects, and product manufacturers. Many systems and products were proprietary; hence, there was an attempt at secrecy. Also, many products were used without proper testing, not to mention poor craftmanship caused by owners and build- ers cutting comers with construction budgets and timetables. Most systems and products were developed through trial and error. It was an age of exploitation of building materials and systems. Today we are left with that legacy. Unfortunately, the preservation of some of these buildings may be financially impossible. Of course, other early build- ings and systems show little potential for failure or severe deteriora- tion; therefore, little should impede their successful preservation. Research for this paper was based on published literature of the period. Unfortunately, few records of building failure were kept, and rarely were ineffective building products or systems criticized by writ- ers of the time. Thus the findings of this report relate to the comparison and evaluation of known building and product failures. Clearly, more research should be done to support further many of the deductions presented here.

OCR for page 211
Diagnosis of Nonstructural Problems in Masonry Buildings OVERRIDING CONDITIONS 213 Several aspects of good building practice that are generally known today were rarely understood previously. Major examples are described here. First, it has Tong been recognized that when choosing a building stone or brick, one should match the expected weathering performance of the material to its expected use or exposure. Thus, stone at the top of a wall or at the cornice must be more durable and more capable of withstanding severe weather than stone on the Tower part of the wall. However, in the competitive building market this was not generally understood; hence, the most durable materials often were not selected for use where they were most needed. Today, deterioration of such weak stones or poor quality brick is common. The materials were simply used incorrectly. Second, ornately carved stone may not be practical where exposed to extreme weather. There is an incongruity here in that soft stone, which is easiest to carve, is generally the least durable. Thus, a heavily carved balustrade at the top of the wall is the worst possible location for soft stone. Unfortunately, this point was often ignored, so we are now faced with treating severe deterioration of stone or brick that has little hope of lasting very far into the future. Third, there are many cases of chemical and physical incompatibil- ities among building materials. Some examples such as acids with limestone or salts within masonry are obvious. But other examples are less obvious, as in the following: Portland limestone and brick. Rainwater washing down limestone onto brick will result in stains and surface damage to the brick. There is little that can be done to arrest this process. Portland cement and calcareous stones. Ferrous oxide in Portland cement will always stain limestone, marble, and some sandstones. Nonstaining Portland cement has been developed to eliminate this problem. Iron, steel, and copper with masonry. Oxidation of these metals can cause both staining and physical damage to stone and brick. Careful attention must be paid if these materials come in contact with ma- sonry. Fourth, overall building profiles have changed. A comparison of a wall section from an eighteenth century stone building and one from

OCR for page 211
214 CONSERVATION OF HISTORIC STONE BUILDINGS the mi`~-twentieth century would clearly show the evolution away from control of rainwater on the face of a building. The early building would have a projecting cornice, pediments over each window, pro- jecting belt courses, and a water table. AD these features were intended to direct rainwater off the face of the wall, minimizing staining, weath- ering, and other moisture problems. In contrast, facades of recent build- ings are comparatively flat, with little or no attention to the control: of rainwater. Thus, moisture problems can be cornrnon. WALLS The most basic element of a building is its walls. For the purpose of this report it is shown that walls have evolved through time from simple bearing walls, to "cavity walls" (bearing walls with a vertical air cavity), to nonbearing "curtain" walls. In most instances, non- bearing walls replaced bearing walls t with the exception of residential- scale buildings) beginning in the 1880s and were in common use by the turn of the century. This is one of the most interesting evolutions in terms of changing technologies, introduction of new building ma- terials, adaption of traditional designs, and new engineering ap- proaches. Bearing Walls To diagnose problems in masonry bearing wails properly one must understand the typical building practices employed. Cut stones of from 10 in. to more than 36 in. wide were laid one on top of the other, always with their bedding planes in their natural "horizontal) position. Brick walls were built up of two, three, or four wythes solidly packed with mortar. The mortar was normally soft, since it was made prin- cipally of lime. Its purpose was to form a uniform bearing plane be- tween masonry unitsin effect, to hold the units apart. It did not hold the units togetherthat is, it did not create adhesion. Problems can now occur with these simple wall constructions where individual stones are connected with dowels, anchors, or cramps (see Figure 11. Such devices were often used with projecting stones (at a cornice or over a window) to provide a sufficient tie or connection to the main bulk- of masonry. Before the widespread availability of steel By the late nineteenth century), these metal anchors were generally made of wrought iron. They were anchored into the stone with molten lead, a sulfur and sand mix, or a mortar grout. The wrought iron generally provided resistance to severe corrosion as long as it was

OCR for page 211
Dia.gnasis of Nonstructural Problems in Masonry Buildings ,~ 215 FIGURE 1 Early anchorage devices. Two types of cramps for clamps) are shown at the left, and a dowel is at the right. These were made of wrought iron, sometimes in cast iron, later in steel, and occasionally in bronze or copper. sufficiently buried within the wall to remain dry. Severe corrosion would occur upon exposure of the anchors to the weather, often jeop- ardizing the integrity of the connection. This comb- result in a failure or collapse of the stonework affected. It is now known that wrought iron, cast iron, or steel anchors set in sulfur or in mortar can become severely corroded if moisture reacts with the sulfur (forming sulfuric acid) or with the mortar (forming carbonic acid. If such conditions exist, one should attempt to inves- tigate all connections to determine the degree of deterioration. Un- fortunately, thorough investigation is rarely feasible, and drastic mea- sures such as complete removal of masonry may have to be considered. However, this is rare, and in the universe of potential nonstructural problems in masonry construction, bearing walls are the least prob- lematic. Cavity Beanng Walls By the early nineteenth century, it was widely recognized that walls of solid masonry were susceptible to moisture penetration from hard- driving rain. To prevent this penetration of moisture from the outside, a vertical air space or cavity Of perhaps 2 to 4 in.) was introduced into the center of the wall {see Figure 21. Thus, two wall sectionsthe outer of dressed stone or hard-fired bricks and an inner of backfill rubble stone or irregular brick were laid independently, yet simultaneously. Generally both were bearing the weight of the wall above, except in very thick walls, perhaps more than 24 in., where the weight was carried on the inner wall. The cavity was designed to provide an outlet for the moisture that penetrated the outer wall. The moisture would flow to the base of the

OCR for page 211
216 FIGURE 2 Typical brick bearing wall construction. Lois detail for common residential scale buildings shows the wall cavity with corru- gated metal ties (probably of galva- ruzed steell. SOURCE: Architectural Graphic Standards, 1936, p. 16. CONSERVATION OF HISTORIC STONE BUILDINGS l ~ Ad. ~ . ~1 _ ~ . |~ . NO- ~ ~ ~ . l ~ ~ , . ~ ~ _ ~ _ = = _ Of .' _ Cam . ;~ ~ __ ~ 77 _ ~) ~ . Ron ~ ~ ~ . ~3 it; IO-TfflCt~ I' 2 THICK _o~^'~'4~~ Jeff Cons~ our a,, I, ~ - ~~ 1 ^~ ~ , 1~ z. For ,_ C77~ _ ~ Add rem it: ED r7; Vat _~ ~ ~ ; rKA V~V/~ . . .. am= am - ~ Fly hi cavity and through weep holes or other small openings toward the outside (either toward an interior crawl space or to the exterior at the base of the wall). The wall sections were positively tied together, either with various types of metal ties or with bond stones, bricks, or structural terra-cotta turned at right angles to the face of the wall and bridging across the cavity to the inner wall section. The metal ties were first made of wrought and cast iron; then, by the mid-nineteenth century, galvanized iron, painted iron, iron dipped in tar, and even copper or bronze were used. Early literature shows that some of these cavity-wall ties were shaped to reduce corrosion problems by eliminating flat surfaces (po- tential catch basins for moisture in the cavity). Figure 3 illustrates some of the variations. There are a host of typical problems with cavity walls. First, there can be differential settlement between the inner and outer wall sec- tions, weakening or even breaking ties between the two and thus jeopardizing the structural integrity of the wall. Second, during con- struction, the cavity can become filled with mortar or debris, clogging weep holes or resting on top of the metal ties and thus creating a small

OCR for page 211
Diagnosis of Nonstructural Problems in Masonry Buildings ''L FIGURE 3 Typical metal cavity-wall ties. These ties could be of galvanized or painted iron and steel, copper, bronze, or even plastic. They are shaped with the special twists or corrugations to prevent water from standing on any flat surfaces. 217 catch basin for moisture. Third, the metal anchors jespecially painted ones or those of galvanized iron) are susceptible to corrosion because the air cavity is often very moist. Therefore, through time these metal ties have often failed because of corrosion, which results in a loss of the wall's structural integrity. Cavity-wall construction can be identified through physical probing, which involves careful core drilling or discreet dismantling of a portion of a wall, or with various nondestructive techniques. Naturally, any original architectural or engineering drawings and/or building speci- fications are invaluable in the identification and diagnosis procedures. Nonbeaiing or Curtain Walls Probably the most interesting topic area in this report is the devel- opment of the curtain walls and skeleton steel and concrete construc- tion of the first part of the twentieth century. Such walls were rarely thicker than 12 in., and their weight was carried either on each floor or on every other floor, supported by the floor framing. Obviously, there were many changes in the technology of construction and types of building materials used. Elevators, skyscrapers, fireproof construc- tion, and lightweight building skins were some of the major elements and new technologies developed during this period. To explore those

OCR for page 211
218 CONSERVATION OF HISTORIC STONE BUILDINGS developments is beyond the scope of this report, but the evolution of the curtain wall itself is of central interest. The first issue is in the change of materials. Bricks or stones, which are quite heavy and capable of supporting themselves, naturally had little use in a curtain wall. The key function was to provide a light- weight enclosure, albeit a decorative one. Strength was not an issue. Incus, sanguine bricks, architectural terra-cotta, cast stone, glass, metal sandwich panels, and so forth were ah substitutes for traditional ma- sonry. Because they were lightweight and nonbearing, they had to be extensively tied back to their masonry back~ng-and to the structural supports. The types of anchors varied greatly, both in shape and in materials, but all were intended to be noncorrosive. The most common materials used were painted or galvanized iron and steel wires. In some cases, bronze or copper ties were used, and recently, various plastic materials have been tried. The shapes varied, from wires (a minimum of #8 gauge or about 1/8 in. in diameter) tied to the masonry unit and to the backing {see Figure 4l, to shaped or bent pieces, or to sheets of wire cloth. With either brick or terra-cotta, these wires or ties were needed continuously throughout the wall, often spaced as closely as 8 in. centers both vertically and horizonally. In the early part of this century, painted steed was considered non- corrosive. This was found to be untrue after a time it corroded baby so galvanized steel became the minimum required. Stainless steed was introduced after World War II, but galvanized and painted iron never fell out of favor. They may still be used today on "budget" jobs, but they are not considered to have anywhere near the life expectancy of stainless steel. Note, however, that some of the early stainless steels have proven to be corrosive. One must be careful when selecting from several grades available today to assure that an anchorage device ca- pable of withstanding the corrosive conditions within a wall is chosen. Generally, types 301 and 302 are satisfactory today. An ancillary problem with materials is that the facing stone on curtain walls is often only 2 in. thick and generally face bedded rather then bedded in its natural plane. The result can be delamination and extensive surface spelling. Stone with the potential for delamination must be laid in its natural bedding plans. A second issue is the wall cavity. There was no question that a cavity was efficient at preventing moisture penetration from the rain. The evolution and treatment of the cavity in curtain-wall construction is interesting. In early curtain walls, the cavity was treated just as it had been in bearing wails. That is, there was an outer veneer of stone, brick, or terra-cotta (generally 4 in. thick), then the air cavity (from 2

OCR for page 211
Diagnosis of Nonstructural Problems in Masonry Buildings 219 t.' ~ it ~ :. ~1 ~ :i ~ ~ 1 ~ 1 ., .,,,, . . 1 ~' ~ o ~ l~. . . ~ . ,,1 _ ;r .~ K . ~ ~ . At_ _ _ i" 'his 1~ T ~:~ ~ ~o~ I i o 1~! TIC ~ jig r I ~ ~, ~ ~ ~ BE - `~ . FIGURE 4 Anchorage techniques with terra-cotta. Each piece is individually tied back with metal wires to the backup masonry and the structure. SOURCE: Masonry: A Short Textbook, 1915, p. 86. to 4 in. thick), and then the inner masonry backup material resulting in a total wall thickness of about 12 in. With this type of wall, new details had to be devised to sheath the structural iron with masonry. Figure 5 is an example. Note that the structural iron was encased with stone, that the resulting cavity was vented to the outside (note words "open joint"!, and that the stone was anchored with metal ties. Although the encased iron and steel was painted, often with up to three coats of iron oxide paint, corrosion was still common. To correct this problem, the cavity was eliminated anCi all steel or iron was thoroughly covered or encased with mortar grout. However, the resulting solid masonry wall could suffer moisture

OCR for page 211
220 FIGURE 5 Stone encasement for floor beams. The stone is a veneer, A; with a seeable Hoer wall cavity to prevent rain penetration. However, rain penetration was still found to be a problem, and corrosion to the steel was common. SOURCE: Archi- tectural Engineering, 1901, p. 154. CONSERVATION OF HISTORIC STONE BUILDINGS , - . _~- a_ . I i it's ' , ~ ' ,/~sw/rf ho _: .1 ,~4S~C~/Y ~~//6fH0~ ~0 \';;'." `\' ~ ^~ Elf At.,. , . ~ .~ 7-T mu, , ~ i, _ , ;t , ~ ,,.,.,.t Hi - -endow , '~ '~ or ar~~ . . ~ ~ . .~- ;~./j/~;,7 I,/ {i/,. /; ' ',:`f, >/~, r/~,/,'/,/if ~o~o/~r . ':~`''~'! ~ l - ~ - yelp-.] penetration, causing disruption to the interior wall finishes. Therefore, the inner plaster was not placed directly on the masonry, but rather on furring strips, resulting in a 1/2 in. air cavity. This is often known as a "funed" wall and is now the preferred detail. The third issue is related to problems with anchorage and to changes in the cavity wall. It concerns the addition of flashing within the wall cavity at selected points to protect critical connections and anchors. Figure 6 illustrates the best in building practice in this regard after World War II. Note particularly the flashing at the spandrel beam, which protects the steel shelf angle at the window from moisture flowing down the cavity. Since this arrangement represents the best in practice, it can be assumed that many recent buildings would not

OCR for page 211
Diagnosis of Nonstructural Problems in Masonry Buildings ,' Wa sly '.~_ Coping Thea {lowing ~ I!tarap~t Spandrel b - FtasPr~r~g 771Y7733 ~3 Z~ // / in,, KA~ iG/=K 4iiz An, r777~ p~ Dry p | ~ banal do - Q at CO' , Cap or Count~lasir~ng ~ ,4 S. ; Rebuilt fop . ~ ~1 . I, Sill swag ~ ~~orrc~r"~oc~ ~ or pollo~T'Ic ~- _ {/~ ~ L L ~ .. I,, T~~-v~all. Flas~irrg ~? on Dcl~npc~=cic" ~ . . . Projecting Coursc1: ~ . C orifice. I: .- . lilt Course ~ v I bass ~ ~ _ . A ' _ `~. - r,,~~7~ 0. . ~ o':ol _~ Fo~niatior~ Mall 221 FIGURE 6 Wall flashing. Note the extensive use of wall flashings, es- pecially at the spandrel beam and below the window sills. Ibis prac- tice is comparatively recent and would rarely be found before World War II. Note also that the inner plas- ter is furred out from the wall. SOURCE: Materials and Methods of Architectural Construction, 1964, p. 213. have this type of flashing and, therefore, that there are some critical areas not adequately protected. The fourth issue is the mortar itself. Lime mortar expands and con- tracts with changes of temperature or moisture content. In a bearing wall, the mortar joint is strictly in compression, and the expansion or contraction of materials has little effect on the structural integrity of the wall. With the evolution of the curtain wall, builders changed to a stronger, waterproof, Portland cement mortar, usually a mixture of

OCR for page 211
222 CONSERVATION OF HISTORIC STONE BUILDINGS one part cement to one part sand. The precise reason for the change is not clear. There was, however, a reference to lime mortar's failing in a fire, and there was the need to make the joint as waterproof as possible to protect the anchorage devices and structural framework (Portland cement mortar is nearly impermeable). The result recognized today is that these high strength cement mortars fail to prevent rain penetration. There are three obvious reasons for this: Portland cement mortars shrink upon setting. Since a curtain wall is not strictly in compressor, minute horizontal fractures from shrink- age occur. This has long been recognized. Often an elastomeric joint sealant or caulking was used in selected horizontal joints around a building, generally at the top of each section of the curtain wall where it joins a floor or spandrel beam. Through the years these joints open up, creating an entry point for rain. In tall buildings, lateral wind loads have the effect of opening up joints on the windward side of a building, placing tensile forces on the curtain wall. Obviously this breaks the mortar bond with the masonry, creating thousands of entry points for rain. Portland cement reacts with airborne sulfates, resulting in "sulfate attack." This causes expansion of the mortar, disrupting the mortar bond with the masonry. These problems taken together create the potential for severe de- terioration of curtain wall materials, especially iron and steel anchorage and structural systems. There may be some extant buildings suffering the worst of these problems that are time bombs waiting to go off. Left unattended, such deterioration could result in severe damage to individual building elements or, in extreme cases, in a failure of a structural component. To counter these potential problems, modem high-rise buildings rely heavily on flexible joint sealants. If the best materials or techniques are not used, the results can be disastrous. TOP OF THE WALL PARAPETS AND CORNICES Parapets A parapet is one of the architectural elements perhaps most susceptible to deterioration and damage. Because it is freestanding and not warmed by interior building heat, it is exposed to the worst weather and is subjected to harsh freeze/thaw cycling.

OCR for page 211
Diagnosis of Nonstructural Problems in Masonry Buildings 223 Builders have recognized the vulnerability of parapets and have gone to great lengths to provide protection to parapet walls. Such a wall must be topped with a capstone Also called a coping!. Figure 7 illus- trates the best practice with a capstone: The top is sloped to provide a water wash, and the stone extends beyond the face of the wall, with a regret or drip on the underside. Where one capstone is joined to another, the mortar joint is very susceptible to water damage because it faces up. Hence, it is often packed with lead or tar or is actually flashed with galvanized iron or copper. This explains the best building practice regarding capstones, and little has changed from medieval times to the present. There can be problems, however, even with capstones like the one in Figure 7. The need for flexible joints to accept horizontal thermal expansion in the parapet wall does not appear to have been recognized until early in this century. Without an expansion joint, the capstone can become dislodged, creating vertical points for water to enter the stone, brick, or terra-cotta parapet wall below. Now, expansion joints are recommended every 20 linear feet. Cornices and Overhangs In a building of simple bearing-wall construction, a stone cornice would merely be corbelled or cantilevered out beyond the stone below. Some- times these cornice stones would have to be tied back to the main _,,w, ,~ ~ ,,, - r ~ A_ 1,_ a. ~'--J---"T----- '---I ~.,.52 t.;~$,"'~--.~. ~~' FIGURE 7 Typical capstone. The sloping surface (a) is called a wash and assures that water will not stand on the top surface. The "re- "let" or "drip" (bl prevents water from flowing under the capstone and down the wall. SOURCE: Ele- meets of Bnck and Stone Ma- sonry, 1930, p. 39.

OCR for page 211
224 CONSERVATION OF HISTORIC STONE BUILDINGS wall with wrought iron cramps. The cramps might be inadvertently exposed to the weather and require ongoing surveillance and main- tenance to avoid serious corrosion and damage to the stonework. As buildings became taller, and architects wanted to preserve some of the proportional relationships between the base, shaft, and capital or cornice of a building, the cornices became massive overhangs of stone or terra-cotta, suspended from the structure's frame. Figure 8 illustrates one such cornice, an extreme example of poor design and naivete in Understanding the potential for problems. The uppermost horizontal surface would have been roofed, probably with a form of composition roofing and.gravel, with collected rainwater draining into interior leaders or downspouts. The potential for failure of this building assembly is great. The bolt heads and nuts under the soffit are exposed to the weather, and other steel angles are very close to the surface of the stone (at points a and b, and susceptible to corrosion. Finally, composition roofing rarely lasts it, id.., .., .. ,, ~ _ _ I Gil Cow ~ ''go o o o ~ .? FIGURE 8 Projecting stone cornice. This stone cornice was na- ively designed. The bolt heads under the soffit are actually exposed to the weather and several angle irons {a and b) are perilously close to the outside face of the stone. SOURCE: Architectural Engineering, 1901, p. 176.

OCR for page 211
Diagnosis of Nonstructural Problems in Masonry Buildings 225 beyond 30 years without some cracks and leakage occurring. For water to enter this assembly would be disastrous. Although this is an extreme example, there are more than a few recorded cases where a piece of a stone or terra-cotta cornice has dropped to the ground. A related development in cornice design is illustrated in Figure 9. Rather than sloping the top surface of the cornice stone outward, it was sloped inward to channel the collected water into the roof's drain- age system. This change was brought about because the former design caused water to Din off the cornice, thus staining portions of the wall below. Unfortunately, although the new design may have reduced staining, it greatly increased the potential for deterioration of the flash- ings and damage to the cornice and parapet because the rainwater is collected, rather than allowed to run off. Wherever water collects, the potential for damage is greatly increased. This new design for a cornice is not an improvement; it is a potential contributor to wall damage. Roof Drainage A not-so-subtle change in roof drainage has also occurred through time. The most common early technique was to pitch the roof (hip, gable, or garnbre} roofs) and direct rainwater off and away from the building. Later, gutters and downspouts were added to control the water and assure that it was properly transported down and away from the base of the wall. Eventually, as buildings got taller, the downspouts Most often of cast iron) had to be built into the wall. Two potential problems were created by this approach. First, if the downspouts were too close to the outside surface of the wall, they could freeze in winter, possibly fracturing the cast iron. Damage to the wall would result. Second, if the downspouts became clogged with leaves or other debris, it was generally impossible to clean them out because they were encased in masonry. Again, they could leak, causing wall damage. Gutters can also be a source of problems with masonry. In many cases, they are incorporated into a stone or terra-cotta cornice and become hidden gutters. Figure 10 illustrates such a typical gutter in a stone cornice. The gutter could be lined with either copper or lead, but should the metals corrode or crack, or the joints open up, water will enter the cornice and top of the wall and cause darnage. This type of gutter must be periodically inspected to assure that leaves or debris do not block proper drainage.

OCR for page 211
226 CONSERVATION OF HISTORIC STONE BUILDINGS STONE . - _ , r `.~\' _~. '\.'< FIGURE 9 Modem stone cornice. This cornice design directs rainwater toward the roof and a central water control system. The design requires extensive flashing, which is especially subject to corrosion and damage to the surface. SOURCE: Materials and Methods of Architectural Construction, 1964, p. 122.

OCR for page 211
Diagnosis of Nonstructural Problems in Masonry Buildings 9_ | (buffer' . /.t ~ . . ~ V. // ...... ~ %, __ _ 2:~!= , ~ ,.- . . ,; . . .: , 227 . ,,, &c r\ How; ,~ . - FIGURE 10 "Hidden" gutter in a stone conduce. The metal gutter lining, usually . Ah. ///// of copper or lead, is very susceptible to IT; -Gus/. ///// corrosion and damage. Without periodic //// maintenance, gutters can fill with leaves ///// or debns, trapping water that can then cor- / ///// rode the metal lming and cause water to at'+ ~ ~5~ /, seep Into the stone and wall assemblies _ : :~Z~ ~ _ below. SOURCE: Architectural Graphic CON IC ~ W 1 TH GUSTED_ Standards, 1936, p. 34. WINDOW OPENINGS IN MASONRY Sills A common location for masonry deterioration or darnage is at window (and door) openings. Because these openings penetrate wall enclosures, moisture may enter the center portions of the wall. Generally, the damage occurs at the head and sill of the window. Sills must be sloped outward and Undercut with a drip or regret, as shown in Figure 11. This sill is an example of the best practice and is known as a "lug" sill. It is distinguished from a "slip" sill by the fact that its ends are set a few inches into the masonry (see a), whereas the slip sill is shortened and is set within the masonry opening. Slip sills were intended for "economical" construction where Tong building life was not expected. Figure 12 illustrates the points most vulnerable to water damage and also illustrates the staining pattern that often results. Any sill must project beyond the face of the wall below, or staining and deterioration will result there. Because sills are exposed to weather on top and on the front, they are susceptible to deterioration, especially from freeze/thaw cycles. If they are face bedded, serious delamination and spelling can result. Lintels . ., The head or lintel above a window opening is another common prob- lem area. Traditionally, lintels were of wood or masonry. Masonry

OCR for page 211
228 CONSERVATION OF HISTORIC STONE BUILDINGS FIGURE 11 Typical stone window sill. This is a lug sill because its ends are embedded in the ma- sonry (at point al. The sill has a positive wash {at b) and a regret {at dI. SOURCE: Elements of Bnck and Stone Masonry, 1930, p. 39. Ash _I lintels were either a single stone spanning the full width of the opening or a combination of stones or bricks forming an arch. Arches could be flat, segmental, or pointed, but they all carried the weight of the ma- sonry wall above. With the availability of iron and steel angles, masonry arches were eliminated. Figure 13 illustrates a typical installation. Because the angles are partially exposed to the weather, the potential for corrosion is great. Little provision is made for rainwater coming down the face FIGURE 12 Staining from "slip" sills. Water flowing off the sill invar- iably stains the wall and seriously erodes mortar joints in the dam age area j shown with cross hatching!. ~ I 1~

OCR for page 211
Diagnosis of Nonstructural Problems in Masonry Buildings 229 - J.Xonl . JO J ~ ' ~ ; .4 ;~ - a, -Gus ~~d ~ . ~:cr ~ ~1 ~ it' On, [:lGURE 13 Steel angle at a window opening. The steel an- gle must remain painted (both within the cavity and on its bottom face) or corrosion and perhaps failure will result. No- tice the absence of wall flash- ing. SOURCE- Architectural Graphic Standards, 1936, p. 32. Of the wall above and under the lintel. The water would just flow back to the angle, thus increasing corrosion. It is not uncommon when investigating a building to find steel angles at the lintel heavily cor- roded, with enough rust built up to disrupt the masonry above and loosen the anchorage of the angle. In such cases very little can be done; they represent serious repair problems. BASE OF WALLS Problems associated with groundwater, surface water, and related salt or freeze/thaw problems have been reasonably wed understood since the mid-nineteenth century. Building practices 'designed to avoid such problems have remained largely unchanged during this century. Problems beyond the obvious in older masonry foundations generally relate to a breakdown in materials or systems intended to keep water out of basements. For instance, outside surfaces of foundation wads were often coated with cement pargeting or asphaltic mastics. Through the years, these coatings become dislodged and no longer block mois- ture penetration. Damage to the foundations, especially to the mortar, results. For most buildings built on damp soil, footing or foundation drains were quite common, especially during the twentieth century. These

OCR for page 211
230 CONSERVATION OF HISTORIC STONE BUILDINGS drains of clay tile or masonry often become clogged with silt, tree roots, or other organic or animal matter, thus reducing or eliminating drainage of groundwater. Naturally, this could damage the foundations and jeopardize building stability. CONCLUSION The obvious conclusion of this paper is that there are potentially very serious problems that have yet to be identified in many buildings. Early building practices were often slipshod. Many of the materials, techniques, or methods used had not been properly tested. More re- search is needed in several of the areas identified in this paper, but the issues are perhaps the following: There is a need for in-depth research into building practices be- tween the 1880s and the present to be able more fully to understand stone and brick detailing, anchorage and flashing techniques, and as- sembly methods. Such understanding would aid in choosing appro- priate repair and preservation treatments. To further understand early building techniques, more effort should be put into documenting budding failures and into recording buildings being demolished or dismantled. A great deal of information about deterioration and damage to building elements could be acquired in this way. There are many problems with early high-rise buildings. One in particular is the repair of deteriorated mortar joints in masonry curtain walls. In attempting to reestablish a waterproof joint, should traditional "tuck pointing" techniques with a waterproof mortar be used, or should the joints be wiped with a "slurry coat" {a near-liquid cement mixture), or should they be caulked with a modem elastomeric sealant? The advantages and disadvantages of each approach should be investigated. Thermal expansion and wind loading as well as environmental dete- rioration of materials should be considers. The need for vertical and horizontal thermal expansion joints may be well understood today, but few early buildings include any such provision. Work should be done to determine if such expansion joints need to be introduced into early masonry buildings and, if so, how this con be accomplished. Problems from the condensation of interior moisture must be more thoroughly studied in buildings with curtain wall construction,

OCR for page 211
Diagnosis of Nonstructural Problems in Masonry Buildings 231 some of which have no inner cavity to prevent moisture passage. Con- tinual condensation could cause corrosion to the metal anchorage de- vices. Condensation may become an increasingly serious problem as buildings are renovated and their use changes (i.e. from office to res- identiall and as new energy-saving mechanical equipment is added which may not adequately control interior humidity. Study of cost-effective and practical ways to apply thermal insu- lation to masonry walls in early twentieth century buildings must be undertaken. Problems of moisture migration through the wails, in- creased potential of freeze/thaw problems with masonry, and the aes- thetic considerations of adding insulation to interior or exterior wad surfaces should be thoroughly studied. SELECTED BIBLIOGRAPHY Architectural Graphic Standards. John Wiley: New York, 1970. Atkinson, William. An improved skeleton construction, The American Architect and Building News. Jan. 9, 1897, pp. 5-6. Baker, Ira O. A Treatise on Masonry Construction. John Wiley: New York, 1889. Birkrnire, William H. Architectural Iron and Steel. John Wiley: New York, 1894. Croly, H.D. The proper use of terra-cotta, Architectural Record. Jan. 1906, pp. 73-81. Duell, John, and Fred Lawson. Damp Proof Course Detailing. The Architectural Press: London, 1977. Eldridge, H.J. Common Defects in Buildings. HMSO: London, 1976. Elements of Stone and Brick Masonry. International Textbook Co.: Scranton, Pa., 1930. Failure of buildings, The American Architect and Building News. April 25, 1896, pp. 36-39. Freitag, Joseph K. Architectural Engineenng. John Wiley: New York, 1901. Fryer, William J. Skelton construction, Architectural Record. July, 1892, pp. 228-35. Hodgson, Fred. Prachca1 Stonemasonry Self-Taught. Frederick Drake: Chicago, 1902. Howe, Malverd A. Masonry: A Short Text-Book. John Wiley: New York, 1915. Jenney, W.L.B. The dangers of tall steel structures, Cassier. March 1898, pp. 413-22. Kenly, W.W. Preservation of materials, Architectural Record. Nov. 1903, p. 409. Kidder, Frank E. The Architects' and Builders' Pocket-Book. John Wiley: New York, 1916. Lynch, Thomas C. The Masons', Bricklayers' and Plasterers' Guide. Riggs Printing House: Albany, New York, 1892. Marsh, Paul. Air and Rain Penetration of Buildings. The Construction Press: London, 1977. Parker, Harry, C.H. Gay, and J.W. MacGuire. Materials and Methods of Architectural Construction. John Wiley: New York, 1964. Pelton, John L. Adjustable facing Marble facing), The American Architect and Building News. Nov. 28, 1896, pp. 7~5. Preservation of steel in tall buildings, Scientific American. March 16, 1907, pp. 226-27. Ramsey, Charles G., and H.R. Sleeper. Architectural Graphic Standards. John Wiley: New York, 1936.

OCR for page 211
232 CONSERVATION OF HISTORIC STONE BUILDINGS Recommended Minimum Requirements for Masonry Wall Construction. Bureau of Standards: Washington, D.C., 1925. Sturgis, Russell. Stone in American architecture, Architectural Record. Oct. 1899, pp. 17~202. The enemies of structural steel, Scientific American. July 6, 1907, pp. 4-5. The preservation of building stone, The American Architect and Building News. March 19, 1887, pp. 142~3. Webb, Walter L., and W.H. Gibson. Masonry and Reinforced Concrete. American School of Correspondence: Chicago, 1909.