cladding with masonry and concrete

809

Cladding with Masonry and Concrete

• Masonry Veneer Curtain WallsPrefabricated Brick Panel Curtain

Walls

• Stone Curtain WallsStone Panels Mounted on a Steel

Subframe

Monolithic Stone Cladding Panels

Stone Cladding on Steel Trusses

Posttensioned Limestone Spandrel Panels

Very Thin Stone Facings

• Precast Concrete Curtain WallsGlass-Fiber-Reinforced Concrete

Curtain Walls

• Exterior Insulation and Finish System

• Future Directions in Masonry and Stone Cladding

20

Architects Thompson Ventulett Stainback & Associates created a bold pattern of precast concrete sunshades and spandrel panels for the facades of the United Parcel Service Headquarters Building in Atlanta, Georgia. (Photo by Brian Gassel/TVS & Associates)

F R O M CO N CEP T TO R EA L I TY

Seattle University School of Law, Seattle, Washington

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Masonry Veneer Curtain WallsFigure 20.1 shows in a series of steps how a brick masonry veneer (a single wythe of brick masonry separated by a cavity from a structural backup wall) may be applied to a reinforced con-crete frame. The veneer may also be made of stone. The veneer wythe is erected brick by brick or stone by stone with conventional mortar, starting from a steel shelf angle that is attached

Buildings framed with structural steel or concrete are often clad with brick masonry, stone masonry, cut stone panels, or precast concrete. These substantial materials, though in fact they are sup-ported by the loadbearing frame of the building, impart a sense of solidity and permanence. Thin facings of masonry or concrete, however, do not behave the same way as solid loadbearing walls. When mounted on a frame, these brittle materials must adjust to the movements of the frame and maintain weathertightness despite being applied in a layer only a few inches thick. Careful detailing and good construction practices are required to make this possible.

810

Figure 20.1Construction sequence for a brick veneer curtain wall supported by a reinforced concrete frame. (a) Before the concrete frame of the building was cast, inserts were put into the formwork to form attachments for the brick veneer, including wedge anchors along the line of each shelf angle, two vertical dovetail slots in each column, short vertical dovetail slots in the spandrel beams, and horizontal reglets in the centers of the spandrel beams to accept the inner edge of a fl ashing over each window head (see pages 624 and 625 for pictures of these inserts). To begin installation of the brick veneer, a steel shelf angle is bolted to each spandrel beam, using malleable iron wedge inserts as shown in Figure 20.2. A slab of polystyrene foam thermal insulation (gray) is placed over the upright leg of the shelf angle, and a continuous fl ashing (white) is installed over the shelf angle, the foam, and the edge of the fl oor slab. This fl ashing also wraps around

the front of the column. All the seams in the fl ashing are overlapped and made watertight with sealant. The fi rst course of brickwork is laid directly on the shelf angle and fl ashing, without a bed joint of mortar. Every third head joint is left open in this fi rst course to form a weep hole. Three courses of brickwork bring the veneer up to the level of the fl oor slab. (b) The fi rst course of the concrete masonry backup wall is laid. Vertical reinforcing bars are grouted into the hollow cores of the backup wall at intervals specifi ed by the structural engineer. An asphaltic coating is applied to the backup wall to act as an air and moisture barrier. Three more courses of brick veneer bring the top of the veneer up to the level of the top of the fi rst course of concrete masonry. Polystyrene foam thermal insulation is placed against the concrete masonry. A combination joint reinforcing and masonry tie made of heavy steel wires is laid on top of the masonry, tying the brick veneer to the backup wall. Plastic clips are snapped onto the tie rods

(a)

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of the joint reinforcing to hold the insulation in position. A vertical expansion joint in the brick veneer is provided at the centerline of each column. A heavy wire masonry tie in a dovetail slot anchors the brick veneer to the column on each side of the joint; another such anchor is lying loose on top of the bricks, ready to be installed, in this view. (c) The wall rises in vertical increments of 16 inches (400 mm), which equals six brick courses or two concrete masonry courses. This is also the vertical distance between ties and the height of a polystyrene foam insulating panel. A-blocks (see Figure 9.23) are utilized as needed in the backup wall to avoid having to thread blocks over the tops of the vertical reinforcing bars. The vertical expansion joint is sealed with backer rod and sealant. As an alternative to the sequence of operations illustrated here, the backup wall and air barrier may be installed to their full height fi rst, followed later by the installation of insulation and veneer.

(b)

(c)

Masonry Veneer Curtain Walls / 811

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812 / Chapter 20 • Cladding with Masonry and Concrete

to the structural frame at each ß oor (Figure 20.2). The construction pro-cess and details are essentially the same as for a masonry cavity wall of a single-story building, but there are some crucial differences: To prevent normal movements in the frame of the building from stressing the ma-sonry veneer, and to allow the veneer to expand and contract without dis-tress, there must be a soft joint (horizon-tal expansion joint) beneath each shelf angle (Figure 20.3). This joint must be dimensioned to absorb the maximum anticipated sum of column creep, brick expansion, spandrel beam de-ß ection, and a dimensional tolerance to allow for construction inaccuracies while not exceeding the maximum safe compressibility of the sealant. Masonry curtain walls also must be divided vertically by movement joints (vertical expansion joints) to allow the

frame and the masonry cladding to expand and contract independently of one another (Figure 20.4).

A backup wall of light gauge steel studs covered with water-resistant sheathing panels of gypsum or ce-mentitious materials is often consid-

ered to be interchangeable with a concrete masonry backup wall for a masonry facing. The stud wall even has certain advantages over masonry in its lighter weight, its greater abil-ity to contain thermal insulation and electrical wiring, and its greater

Figure 20.2(a) An example of a cast-in-place anchoring system for attaching a steel shelf angle to a concrete spandrel beam. Steel shims are added as necessary between the shelf angle and the spandrel beam to place the angle exactly in the plane of the facing wythe. (b) The traditional method for attaching shelf angles to steel spandrel beams uses steel clip angles with shim plates as needed to make up for dimensional inaccuracies in the components. In practice, providing anchoring systems with adequate adjustability to account for deviations in the structural frame is often a diffi cult challenge.

(a)

(b)

Figure 20.3A complete detail section of the brick veneer wall that was begun in Figure 20.1 shows how the top of the backup wall is fastened to the underside of the spandrel beam with

a series of steel restraint clips that brace the top of the wall against wind loads but allow the spandrel beam to defl ect under load. Two lines of backer rod and sealant

along the columns and across the top of the backup wall make the backup wall airtight. A soft joint of sealant beneath the shelf angle permits the spandrel beam to defl ect

without applying force to the brick veneer. The brick ties nearest the underside of the shelf angle are anchored to dovetail slots in the spandrel beam. An additional plastic

clip on each wire tie in the center of the cavity acts as a drip to prevent water from clinging to the tie and running toward the backup wall. The interior of the building is fi nished with gypsum veneer plaster mounted on steel furring channels, similar to the

assembly shown in Figure 23.5. (Drawing from Allen, Edward, Architectural Detailing: Function, Constructibility, Aesthetics, New York, John Wiley & Sons, Inc., 1993, reproduced

by permission of the publisher)

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receptivity to a variety of interior Þ n-ish materials. However, the steel studs and their fastenings are inherently more ß exible than a concrete ma-sonry wall and may deß ect enough under maximum wind pressures to cause cracking of brittle masonry ve-neers. Such cracking often leads to water leakage. Furthermore, if there is leakage through the facing layer of the wall because of cracking, porous masonry, or poor workmanship, the steel studs and fasteners are suscep-tible to corrosion, and the gypsum sheathing panels are subject to water deterioration.

A concrete masonry backup wall is usually stiffer than the veneer that

it supports, so the veneer is unlikely to crack under wind loadings. A con-crete masonry backup wall can also, if necessary, maintain its structural in-tegrity despite prolonged periods of wetting. For these reasons, a concrete masonry backup wall is generally preferable to a wall of steel studs. If a steel stud backup system is selected, the studs, masonry ties, and fasteners should be sized very conservatively so as to be stiff enough against wind loadings that the veneer material will not crack. The sheathing material and fasteners should be selected for their durability under damp condi-tions. Each metal tie that connects the masonry veneer to the studs should

be attached directly to a stud with at least two corrosion-resistant screws. The wall must be detailed carefully to keep leaked water away from the back-up components. Constant inspection is required during construction to be certain that all these details are faith-fully executed and the cavity is kept clean so that it will drain freely.

The structural frame of a build-ing is never absolutely ß at or plumb. Thus, the attachment system for the shelf angles must allow for adjust-ments so that the masonry veneer may be constructed in a precisely vertical plane with level courses. Figure 20.2 shows how this is usu-ally done for both concrete and steel

Figure 20.4(a) A carefully detailed brick curtain wall by architects Kallman, McKinnell and Wood covers the steel frame of Hauser Hall at Harvard University. Notice the vertical expansion joint near the far-right corner. (b) At the base of Hauser Hall, the facing wythe is made of limestone blocks. The backup wall consists of steel studs and gypsum sheathing panels. A vertical expansion is visible in the far-left corner in this view. (Photos © Steve Rosenthal)

(a) (b)

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frames. The attachment system in Figure 20.5, which is designed to sus-pend a masonry veneer spandrel wall over a continuous band of windows, also provides for free adjustment of the shelf angle location.

The ß ashing above the shelf an-gle should project beyond the face

of the masonry by 1 inch (25 mm) or so and should be bent downward at a 45-degree angle to form a drip. In this way, it is able to conduct water that has leaked into the cavity back to the outdoors and to drain it safely away from the wall. If a ß exible plastic or composite ß ashing is used, it should

be cemented to a strip of sheet metal ß ashing over the shelf angle, with the sheet metal forming the projecting drip.

Many architects, because they wish to maintain the Þ ction that a masonry veneer is actually a solid masonry wall, Þ nd the soft joint and


Figure 20.5A detail section of a brick curtain wall that is supported below the level of the spandrel beam on a frame made of steel angles. The supporting frame becomes necessary when continuous horizontal bands of windows are to be installed between brick spandrels. All the connections in the supporting frame are made with bolts in slotted holes to allow for exact alignment of the shelf angle. After the frame has been aligned and before the masonry work begins, the connections are welded to prevent slippage. Shelf angle constructions for masonry curtain walls require careful engineering to accommodate expected loads and structural defl ections.

Figure 20.6The detail shown in Figure 20.5 allows the construction of brick spandrels between continuous horizontal bands of glass. (Photo by Edward Allen)

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projecting ß ashing objectionable. They use specially molded bricks with a face lip that hangs down over the shelf angle to conceal it from view, and they do not allow the ß ashing to project out of the wall. The color of the sealant that they use in the soft

joint is matched as closely as possible to the color of the mortar. Unfortu-nately, the use of lipped bricks and recessed ß ashings is very risky. The recessed ß ashing allows water to accu-mulate around the toe of the angle, causing the angle to rust. Freeze-thaw

action and the expansion of the steel as it rusts are likely to cause the lips to spall off of the bricks. Eventually, the deterioration along the line of the shelf angle becomes unsightly. Worse yet, the stability of the veneer may be endangered by failure of the

Figure 20.7Fabrication and installation of a brick panel curtain wall. (a) Masons construct the panels in a factory, using conventional bricks and mortar. Both horizontal and vertical reinforcing are used, the vertical bars being grouted into the hollow cores of the bricks. (b) Brick panels are stored to await shipment, complete with thermal insulation. The welded metal brackets are for attachment to the building; the structural strength of the panel comes primarily from the reinforced masonry, not the brackets. (c) A crane lifts a parapet panel to its fi nal position. (d) Corners can be constructed as single panels. (Panelized masonry by Vet-O-Vitz Masonry Systems, Inc., Brunswick, Ohio)

(a) (b)

(c) (d)

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Stone Curtain Walls / 817

corroded shelf angle. A better strat-egy for the conscientious architect is to Þ nd a way to express visually the presence of the shelf angle, ß ashing, and soft joint, and to make them posi-tive features of the building facade. A soldier course or cut stone sill above each shelf angle is a good start toward a frank expression of a constructional necessity.

Prefabricated Brick Panel Curtain Walls

Figure 20.7 shows the use of prefabri-cated reinforced brick panels for cladding. Masons construct the panels while working comfortably at ground level in a factory. Horizontal reinforcing

may be laid into the mortar joints or grouted into channel-shaped bricks. Vertical reinforcing bars are placed in grouted cavities of hollow-core bricks. These panels are self-rigid; they need no structural backup and can be fas-tened to the building in much the same way as precast concrete panels. A steel stud backup wall is required to carry thermal insulation, electrical wiring, and an interior Þ nish layer, but it has no structural role.

Stone Curtain WallsChapter 9 discusses types of stone and illustrates conventionally set stone facing systems that tie relatively small

blocks of cut stone set in mortar to a concrete masonry backup wall. Slabs of stone that are larger in surface area may be fastened to framed buildings in several different ways.

Stone Panels Mounted on a Steel Subframe

Figure 20.8 shows a system for mount-ing stone panels on a steel subframe, called grid-system-supported stone clad-ding. The vertical members of the subframe are erected Þ rst. They are designed to transmit gravity and wind loads from the stone slabs to the frame of the building. The horizon-tal members are aluminum shapes that engage slots in the upper and

Figure 20.8A subframe of vertical steel struts supports a facing of stone panels by means of horizontal metal clips that engage slots in the upper and lower edges of the panels. In order to avoid corrosion and staining problems, the steel struts should be galvanized, and the clips should be made of a nonferrous metal (aluminum or stainless steel) that is chemically compatible with the type of stone that is used.(a)

(b)

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Figure 20.9(a) Parapet and (b) spandrel details for a stone panel curtain wall made

of limestone, marble, or granite. The broken lines indicate the outline of the

interior fi nish and thermal insulation components, which are not shown.

Each support plate holds edges of two adjacent wall panels, which are pocketed

as shown to rest on the plate. The plate should be made of a noncorroding

metal. The vertical joints between panels are closed with a backer rod and sealant.

(a)

Figure 20.10A granite panel curtain wall of the type

illustrated in Figure 20.9 wraps around the corner of a Boston offi ce building. The upper-fl oor windows have not yet been installed, but

the window frames have been mounted in two of the middle fl oors, and the lower fl oors have been glazed. (Architect: Hugh Stubbins and

Associates. Photo by Edward Allen)

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(b) lower edges of each panel to attach them Þ rmly to the building. They are added as the installation of the stone panels progresses. Backer rods and sealant Þ ll the spaces between the panels, allowing for a considerable range of movement. A nonstructural backup wall, usually made of steel studs and gypsum sheathing panels, is constructed within the frame of the building but is not attached to the subframe. Its functions are to pro-vide an air barrier, to house thermal insulation batts and electrical wiring, and to support the interior wall Þ nish layer, which is usually plaster or gyp-sum board.

A weakness of this system is its de-pendence on the integrity of the seal-ant joints. If a sealant joint leaks, wa-ter may accumulate in the slots in the tops of the stone panels, and freeze-thaw deterioration may ensue.

Monolithic Stone Cladding Panels

Figures 20.9 and 20.10 illustrate the use of monolithic stone cladding panelsthat are fastened directly to the frame of the building. The weight of each panel is transferred to two steel sup-port plates by means of edge pockets that are cut into both sides of each panel at the stone mill. Each panel is stabilized by a pair of steel angle struts that are bolted to the stone with expansion anchors in drilled holes. Joints are closed with backer rod and sealant, and a nonstructural backup wall is required.


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Figure 20.11A steel truss system for stone cladding.

(a) Masons working in a fabrication yard attach thin sheets of stone to welded

steel trusses. The vertical joints are closed with backer rods and sealant. (b) The fabricated spandrel panel is lifted onto a truck using a crane. The metal clips that are just visible along the top and bottom edges of the panel engage

slots in the edges of the sheets of stone to hold the stone securely to the truss. The steel angle clips at the two upper

corners of the truss will support the panel on brackets welded to the steel

columns of the building frame. (c) The panel is installed. (Courtesy of International

Masonry Institute, Washington, DC)(a)

(b)

(c)

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Stone Cladding on Steel Trusses

In truss-supported stone cladding, sheets of stone are combined into large pre-fabricated panels by mounting them on structural steel trusses (Figure 20.11). Each truss is designed to carry both wind loads and the dead load of the stone to steel connection brackets that transfer these loads to the frame of the building. Sealant joints and a nonstructural backup wall Þ nish the installation.

Posttensioned Limestone Spandrel Panels

Thick blocks of limestone may be joined with adhesives into long span-drel panels and posttensioned with high-strength steel tendons so that

the assembly is self-supporting be-tween columns (Figure 20.12). Such posttensioned limestone spandrel panelsare a relatively costly type of panel because of their use of comparatively large quantities of stone per unit area of cladding.

Very Thin Stone Facings

Extremely thin sheets of stone (as thin as ¼ inch, or 6.5 mm, for gran-ite) may be stiffened with a structural backing such as a metal honeycomb and mounted as spandrel panels in an aluminum mullion system such as those described in Chapter 21.

Very thin sheets of stone may also be used as facings for precast concrete curtain wall panels. The stone sheets are laid face down in the

forms. Stainless steel clips are insert-ed into holes drilled in the backs of the stone. A grid of steel reinforcing bars is added, and then the concrete is poured and cured to complete the panel. The clips anchor the stone to the concrete.

When specifying the thickness of stone for any exterior cladding ap-plication, the designer should work closely with the stone supplier and also consult the relevant standards of the building stone industry. Stone that has been sliced thinner than in-dustry standards has caused a num-ber of failures of cladding systems.

Figure 20.12Thicker blocks of Indiana limestone may be posttensioned together to make spandrel panels that span from column to column but require little steel. The posttensioning tendon is threaded through matching holes that are drilled in the individual stones prior to assembly.


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Figure 20.13A typical detail of a precast concrete curtain wall on a sitecast concrete frame. Panels in this example are a full story high, each containing a fi xed window. The reinforcing has been omitted from the panel for the sake of clarity, and the outline of the thermal insulation and interior fi nishes, which are not shown, is indicated by the broken lines.

Precast Concrete Curtain WallsPrecast concrete cladding panels, both conventionally reinforced and pre-stressed (page 808 and Figures 20.13Ð20.18), are simple in concept but require close attention to mat-ters of surface Þ nish, mold design, thermal insulation, attachment to the building frame, and sufÞ cient

strength and rigidity in the building frame to support the weight of the panels.

The factory production of con-crete cladding panels makes it possi-ble to utilize very high-quality molds and a variety of surface Þ nishes, from glassy smooth to rough, exposed ag-gregates. Ceramic tiles, thin bricks, or thin stone facings may be attached to precast concrete panels. In precast concrete sandwich panels, thermal in-

sulation is incorporated as an inner layer of the panel (Figures 20.17 and 20.18). Alternatively, insulation may be afÞ xed to the back of the panel or may be provided in a nonstructural backup wall that is constructed in place. Reinforcing or prestressing of the panel must be designed to resist wind, gravity, and seismic forces and to control cracking of the concrete. Attachments must transfer all these forces to the building frame while

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Figure 20.14Workers install a precast concrete curtain wall panel. (Architects and engineers: Andersen-Nichols Company, Inc. Photo by Edward Allen)

Figure 20.15A Chicago hotel is clad in precast concrete panels. (Architects: Solomon Cordwell Buenz Associates. Photo by Hedrich Blessing)

Precast Concrete Curtain Walls / 823

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allowing for installation adjustment and for relative movements of the frame and the cladding.

More recently developed materi-als, such as carbon Þ ber reinforcing or ultra-high-performance concrete (see Chapter 15), allow the manufac-ture of panels that are thinner and lighter than those made of conven-tional materials.

Glass-Fiber-Reinforced Concrete Curtain Walls

Glass-fi ber-reinforced concrete (GFRC) is a relatively new cladding material that

has several advantages over conven-tional precast concrete panels. Its ad-mixture of short glass Þ bers furnishes enough tensile strength that no steel reinforcing is required. Panel thick-nesses and weights are about one-quarter of those for conventional precast concrete panels, which saves money on shipping, makes the pan-els easier to handle, and allows the use of lighter attachment hardware. The light weight of the cladding also allows the loadbearing frame of the building to be lighter and less ex-pensive. GFRC can be molded into three-dimensional forms with intri-

cate detail and an extensive range of colors and textures (Figures 20.19 and 20.20).

The Þ bers in GFRC must be manufactured from a special alkali-resistant type of glass to prevent their disintegration in the concrete. The panels may be self-stiffened with GFRC ribs, but the usual practice is to attach a welded frame made of light gauge steel studs to the back of each GFRC facing in the factory. The attachment is made by means of thin steel rod anchors that ß ex slightly as needed to permit small amounts of relative movement between the

Figure 20.16Horizontal bands of smooth and textured precast concrete create the facade pattern of this suburban offi ce building. (Architect: ADD, Inc. Courtesy of Precast/Prestressed Concrete Institute)

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Figure 20.17Manufacturing Corewall®, a proprietary foam-core precast concrete sandwich panel. Rollers apply a ribbed texture to the outside of a panel that includes a layer of foam plastic insulation sandwiched between layers of concrete. (Courtesy of Butler Manufacturing Co.)

Figure 20.18A completed panel is lifted from the casting bed. (Courtesy of Butler Manufacturing Co.)


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Figure 20.19Fabrication of a GFRC wall panel. (a) Concrete and chopped glass fi bers are sprayed into a mold and compacted with a hand roller to create a panel facing. Only the top half of the facing has been applied to the mold in this illustration. (b) A welded frame of steel studs with L-shaped steel rod anchors is lowered onto the back of the facing and held just above it by spacers. Pads of GFRC are placed over the anchors by hand to join the facing to the frame. (c) After overnight curing, the completed panel is removed from the mold and stored for further curing before installation.

(a)

(b)(c)

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Figure 20.20Fabrication of a GFRC curtain wall panel. (a) A special gun deposits a layer of sand–cement slurry simultaneously with 1.5-inch (38-mm) lengths of alkali-resistant glass fi ber reinforcing. Three layers are usually required to make up the full thickness of the panel facing; each is compacted with a small hand roller before the next layer is applied. The overall thickness is usually 1�2 inch (13 mm). (b) After the GFRC facing layer has been completed, the steel frame is lowered over it and the operator hand-applies pads of wet GFRC over the rod anchors to bond the frame to the GFRC facing. (Courtesy of Precast/Prestressed Concrete Institute)

(a)

(b)


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facing and the frame. Figure 20.21 shows typical ways of attaching met-al-framed GFRC panels to the build-ing. The edges of the GFRC facing, which is usually only about 1�2 inch (13 mm) thick, are ß anged as shown in Figure 20.22 so that backer rods and sealant may be inserted between panels.

Exterior Insulation and Finish SystemAn exterior insulation and fi nish system (EIFS) consists of a layer of plastic foam insulation that is adhered or me-chanically fastened to a backup wall, a reinforcing mesh that is applied to the outer surface of the foam by em-

bedment in a base coat of a stuccolike material, and an exterior Þ nish coat of a similar stuccolike material that is troweled over the reinforced base coat. In most cases, EIFS is construct-ed in place over a backup wall made either of concrete masonry or of steel studs and water-resistant sheathing (Figures 20.23 and 20.24), but the

Figure 20.21Typical connections of GFRC panels to a steel building frame. The lower connection in each case is a threaded rod that can fl ex as necessary as the height of the upper connection is adjusted with shims. (Courtesy of Precast/Prestressed Concrete Institute)

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Figure 20.22Typical edge details for GFRC cladding panels. (Courtesy of Precast/Prestressed Concrete Institute)

system also adapts readily to prefab-rication (Figure 20.25). EIFS Þ nds wide use over wood light framing as well, where it is used for small com-mercial and residential buildings.

There are two generic types of EIFS, polymer based and polymer modiÞ ed. Polymer-based EIFS uses a very low density expanded polysty-

rene bead foam insulation, a glass Þ ber reinforcing mesh embedded in a base coat that is formulated pri-marily from either portland cement or acrylic polymer, and a Þ nish coat that consists of texture granules in an acrylic polymer vehicle. The foam in-sulation is adhered to the backup wall. Polymer-modifi ed EIFS uses a slightly

higher density, extruded polystyrene foam insulation rather than expand-ed bead foam. The foam panels are mechanically attached to the backup wall with metal or plastic screws (plas-tic screws minimize thermal bridg-ing through the insulation). A metal reinforcing mesh is embedded in a relatively thick portland cement base

Exterior Insulation and Finish System / 829

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coat, and the Þ nish coat is formulated of portland cement with acrylic modi-Þ ers. Polymer-modiÞ ed systems are more durable (and more expensive) than polymer-based systems. They are more susceptible to shrinkage crack-ing during curing but are much less susceptible to denting or puncture. Polymer-based systems, on the other hand, have a very thin coating that is

more elastic and less prone to crack-ing but relatively easy to dent or punc-ture when applied to areas of a build-ing that are within reach of passersby or vehicles.

EIFS is an unusually versatile type of cladding, used for building types as diverse as single-family residences of wood or masonry construction as well as the largest buildings of noncombus-

tible construction. It is used both for new construction and for refacing and insulating existing buildings. The insu-lating foam layer may be up to 4 inches (100 mm) thick, and there is little or no thermal bridging. The Þ nish layer may be applied in a range of colors and textures. In appearance, at least from a distance, EIFS is virtually indistinguish-able from conventional stucco.

Figure 20.23Four steps in installing an EIFS over a building with walls of masonry or solid sheathing. (a) A panel of foam is daubed with polymer-modifi ed portland cement mortar. The foam may be as thick as required to achieve the desired thermal performance. (b) The foam panel is pressed into place, where it is held permanently by the daubs of mortar. (c) A thin base coat of polymer-modifi ed stucco is applied to the surface of the foam panels, with an embedded mesh of glass fi ber to act as reinforcing. (d) After the base coat has hardened, a fi nish coat in any desired color is troweled on. (Used by permission of Dryvit¨ System, Inc.)

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A weakness of conventional EIFS of either type is that it is designed as a barrier system, without any means of internal drainage to prevent damage to the backup material if water leak-age occurs at joints or through dam-aged areas. There have been numer-ous cases of extensive water damage in EIFS-faced buildings that have ex-perienced leakage through poor de-tailing, faulty sealant joints, or failed coatings, especially around windows and doors. In response to this prob-lem (and to the extensive litigation that arose out of it), EIFS producers now market water-managed or water-drainage EIFS. These systems utilize a layer of drainage matting behind the foam insulation that can capture wa-ter that does leak past the outer layer and conduct it to plastic ß ashings and weeps above wall openings and at the base of the wall, lessening the

Figure 20.24A new bank building clad in EIFS.

(Architect: Paul Thoryk. Photo by John Bare. Used by permission of Dryvit® System, Inc.)

Figure 20.25EIFS cladding can be shop fabricated and erected in panel form. (a) Steel studs are welded together to make panel frames. (b) Rigid sheathing is screwed to the panel frames and fi nished with EIFS as shown in Figure 20.23. (c) The fi nished panels are bolted to the frame of the building. (Used by permission of Dryvit® System, Inc.)

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Figure 20.26A mockup demonstrates the features of a proprietary EIFS system with internal drainage. From interior to exterior, the layers are an asphalt-saturated felt air and moisture barrier, a drainage mat composed of plastic fi bers, plastic foam insulation, reinforcing mesh, a base coat, and a fi nish coat. A continuous plastic fl ashing under a gap at the bottom of the wall drains any leakage out to the face of the wall. (Photograph of Senergy CD System courtesy of Senergy, Cranston, Rhode Island)

CSI/CSC

MasterFormat Sections for Masonry and Concrete Cladding

03 40 00 PRECAST CONCRETE

03 45 00 Precast Architectural Concrete Faced Architectural Precast Concrete

03 49 00 Glass-Fiber-Reinforced Concrete

04 20 00 UNIT MASONRY

04 21 00 Clay Unit Masonry Brick Veneer Masonry04 25 00 Unit Masonry Panels Metal-Supported Unit Masonry Panels

04 40 00 STONE ASSEMBLIES

04 42 00 Exterior Stone Cladding Grid-System-Supported Stone Cladding Stone Panels for Curtain Walls

07 20 00 THERMAL PROTECTION

07 24 00 Exterior Insulation and Finish Systems Polymer-Based Exterior Insulation and

Finish System Polymer-Modifi ed Exterior Insulation

and Finish System Water-Drainage Exterior Insulation

and Finish System

07 40 00 ROOFING AND SIDING PANELS

07 42 00 Wall Panels Fabricated Wall Panel Assemblies

risk of water penetrating deeper into the system, where it can cause greater damage (Figure 20.26).

Another weakness of polymer-based EIFS is the ease with which it is dented or punctured; this problem may be overcome by specifying a poly-mer-modiÞ ed system or a specially re-inforced polymer-based system in ar-eas subject to damage. Damaged spots are easily and unobtrusively patched.

Because of these weaknesses and problems, the designer is advised to proceed with extreme care in detail-ing and specifying EIFS cladding and to avoid the use of barrier EIFS ex-cept in combination with backup sys-tems, such as cast-in-place concrete, that are highly tolerant of moisture intrusion.

Future Directions in Masonry and Stone CladdingThe alert reader will have noticed that most of the cladding systems shown in this chapter are detailed as barrier systems, not rainscreen systems (the notable exception being masonry ve-neer systems with drainage cavities and backup walls). This means that they are entirely dependent on good installation and careful maintenance if they are to remain watertight. If a sealant joint fails or a stone cracks in any of these systems, there is little to keep water from getting behind the cladding. There is also no well-orga-nized system of secondary drainage in these systems: Although most have cavities behind their facings, the cavi-ties are interrupted by framing and attachment components that are likely to splatter draining water onto the building frame and backup wall, where it can cause serious damage.

There have been many isolated efforts to design true rainscreen de-tails for stone and concrete cladding systems, and a number of success-ful projects have been constructed. So far, however, no standard rain-screen details have emerged for these materials. This is an area to which

trade associations and researchers should direct a great deal of effort, because reliably watertight details that are not heavily dependent on

good workmanship and maintenance would save tens of millions of dollars each year in repair and reconstruc-tion costs.

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1. Brick Industry Association. Technical Notes on Brick Construction, Nos. 18, 18A, 21, 21A, 21B, 21C, 27, 28B. Reston, VA, various dates.

These detailed pamphlets cover every as-pect of brick veneer cladding systems.

2. All the references on stone and con-crete masonry listed at the end of Chapter 9 are also relevant to this chapter.

3. Precast/Prestressed Concrete Institute. Architectural Precast Concrete (3rd ed.). Chi-cago, 2007.

This is a well-illustrated hardbound book that covers all aspects of the design, man-ufacture, and installation of precast con-crete curtain walls. Also available from the same source is Architectural Precast Concrete—Color and Texture Selection Guide (2003), an extensive set of full-color plates of Þ nishes for precast concrete panels.

4. Precast/Prestressed Concrete Institute. GFRC: Recommended Practice for Glass Fiber Reinforced Concrete Panels (4th ed.). Chi-cago, 2001.

This 104-page booklet is a clear, complete guide to the design and manufacture of GFRC cladding systems. (Address for or-dering: See reference 3.)

5. Sands, Herman. Wall Systems: Analysis by Detail. New York, McGraw-Hill, 1986.

Though dated, this volume remains a valuable collection of case studies of clad-ding systems, illustrated comprehensively, with detailed drawings, many of them in three dimensions.

SELECTED REFERENCES

Cladding with Masonry and Concrete

AuthorÕs supplementary web site: www.ianosbackfi ll.com/20_cladding_with_masonry_and_concreteBrick Industry Association: www.bia.orgDry-Vit Systems: www.dryvit.comEIFS Industry Members Association: www.eima.comPrecast/Prestressed Concrete Institute: www.pci.orgWhole Building Design Guide, Wall Systems: www.wbdg.org/design/env_wall.php

WEB SITES

masonry veneershelf anglesoft joint, horizontal expansion jointvertical expansion jointbackup wallprefabricated reinforced brick panelsgrid-system-supported stone cladding

monolithic stone cladding paneltruss-supported stone claddingposttensioned limestone spandrel panelsprecast concrete cladding panelprecast concrete sandwich panelglass-Þ ber-reinforced concrete (GFRC)

cladding panel

exterior insulation and Þ nish system (EIFS)

polymer-based EIFSpolymer-modiÞ ed EIFSwater-managed EIFS, water-drainage

EIFS

KEY TERMS AND CONCEPTS

1. List all the common ways of attaching stone cladding to a building. Make a sim-ple sketch to explain each system.

2. Working from memory, sketch all the details of a brick veneer wall over a con-crete frame.

3. What are some options of surface Þ nishes for precast concrete cladding panels?

4. Describe the process of producing GFRC panels, illustrating your account with simple sketches.

5. Name two types of EIFS. Describe two ways of applying EIFS to a building. Why should barrier wall EIFS be avoided?

REVIEW QUESTIONS

1. Design and detail a brick veneer clad-ding for a multistory building that you are designing. Rather than trying to conceal the ß ashings and soft joints, work out a way of expressing them boldly as part of the architecture of the building.

2. Visit one or more buildings under construction that are being clad with masonry, concrete, GFRC, or EIFS. Make sketches of how the materials are detailed, especially how they are anchored to the

building. What will happen to any water that leaks through the cladding?

3. Adapt the brick veneer details in this chapter to installation on a building framed with structural steel.

EXERCISES

Exercises / 833

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http://www.ianosbackfi

http://www.bia.org

http://www.dryvit.com

http://www.eima.com

http://www.pci.org

http://www.wbdg.org/design/env_wall.php

cladding with masonry and concrete

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