Facade Magazinestyle

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DIRECT ADHEREDCERAMIC TILE,

STONE AND THIN BRICKFACADES

TECHNICAL DESIGN MANUAL

Richard P. Goldberg, Architect AIA, CSI


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Direct Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.2

Cover Photo: Project-Xerox Building Santa Ana, CA USA, 1988

Description: 12 x 12 x 3/8 inch ( 300 x 300 x 10 mm) Balmoral red granite over cement plaster, metal lath and steelstuds. Architect-Strock & Associates, Irvine, CA, USA

1998 LATICRETE International, Inc. All rights reserved. No part of this publication (except for previously publishedarticles and industry references) may be reproduced or transmitted in any form or by any means, electronic ormechanical, without the written permission of LATICRETE International, Inc.

The information and recommendations contained herein are based on the experience of the author and LATICRETEInternational, Inc. While we believe the information presented in these documents to be correct, LATICRETEInternational and its employees assume no responsibility for its accuracy or for the opinions expressed herein. Theinformation contained in this publication should not be used or relied upon for any specific application or projectwithout competent examination by qualified professionals and verification of its accuracy, suitability, andapplicability. Users of information from this publication assume all liability arising from such use.


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3

I am pleased that Richard Goldberg has been able to gather and compile

all of the technical information included in this design manual concerning

a subject with which I have been intimately involved with for the last 55

years. The products and systems we have invented allow for the

installation of ceramic tile, stone and thin brick facades in all types of

demanding climates throughout the world. This technology has enabled

the ceramic tile, stone and thin brick industries to advance and keep pace

with the demands of modern building design and construction.

I hope that you will enjoy and benefit from the contents of the technical

information related to direct adhered ceramic tile, stone and thin brick

facades included in this design manual. The information included in this

publication will serve as a design manual for Architects, Engineers,

Design Professionals, Construction Professionals and Ceramic Tile and

Stone Industry Professionals.

Dr. Henry M. Rothberg


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DIRECT ADHERED CERAMIC TILE,STONE AND THIN BRICK FACADES


Richard P. Goldberg, Architect AIA, CSIDirector of Technical Services

LATICRETE International, Inc. USA

ACKNOWLEDGEMENTS

This book was made possible through the support and assistance of many

people. I extend my deepest appreciation to Henry M. Rothberg Founder and

Chairman of the Board of LATICRETE International Inc., for sharing his 50+years of invaluable personal experience as the pioneer of latex cement and

epoxy adhesive technology, and for having the confidence in me to document

that legacy.

Richard P. Goldberg


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IndexDirect Adhered Ceramic Tile, Stone, &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.

DIRECT ADHERED CERAMIC TILE,

STONE AND THIN BRICK FACADES


TABLE OF CONTENTS

SECTION 1 INTRODUCTION..........................................................................................91.1 Preface1.2 Why Use The Direct Adhered Method?1.3 Brief History of Ceramic Tile, Stone and Thin Brick Facades1.4 Summary - Content of Manual1.5 Historical Case Study

SECTION 2 EXTERIOR WALL CONCEPTS......................................................................152.1 Function of Exterior Walls2.2 Types of Exterior Wall Structures

Bearing WallNon-bearing WallCurtain Wall

2.3 Types of Exterior Wall ConstructionBarrier Wall

Cavity WallPressure-equalized Rainscreen WallFuture Technology - Dynamic Buffer Zone

2.4 References

SECTION 3 TYPES OF DIRECT ADHERED WALL CONSTRUCTION.............................213.0 On Site (In-situ) Construction3.1 Concrete Masonry Unit Substrate

Barrier WallCavity and Pressure-Equalized WallInner Cavity Concrete Masonry

Inner Cavity Light Gauge Steel Framing3.2 Clay Masonry Unit Substrate3.3 Light Gauge Steel Framing

Cement Backer Unit SubstrateLath and Cement Plaster SubstrateCorrugated Steel Substrate

3.4 Reinforced Cast-in-place Concrete Substrate3.5 Pre-fabricated Panels3.6 Pre-cast Concrete

Positive CastNegative Cast

Glass Fiber Reinforced Concrete (GFRC) Panels3.7 Architectural Details3.8 Case Study - Saskatoon City Hospital - Precast Concrete and Ceramic Tile3.9 References

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SECTION 4 STRUCTURAL AND ARCHITECTURAL CONSIDERATIONS.......................694.1 Structural Considerations - Types of Structural Movement

Live and Dead LoadsThermal MovementMoisture ExpansionDrying ShrinkageElastic DeformationCreepDifferential Settlement

4.2 Architectural Considerations - Components of the Exterior WallAssembly

Windows and Window Maintenance SystemsThermal Control - InsulationMoisture Control - Waterproofing and FlashingMovement JointsFire Resistance and ContainmentAcoustical ControlRoofing and Parapet Walls

4.3 References

SECTION 5 SUBSTRATES..............................................................................................895.1 Criteria for Selection of Substrates5.2 Types of Substrates5.3 Substrate Preparation - Design and Construction Requirements5.4 Substrate Preparation - Cleaning Equipment and Procedures5.5 References

SECTION 6 SELECTION OF EXTERNAL CLADDING MATERIAL.................................107

6.1 Criteria for Selection of Ceramic Tile, Natural Stone and Thin Brick6.2 Ceramic Tile6.3 Natural Stone and Agglomerates6.4 Thin Brick Masonry6.5 Cladding Selection - Moisture Sensitivity, Color, Temperature6.6 References

SECTION 7 INSTALLATION MATERIALS AND METHODS - ADHESION....................121GROUTING OF CERAMIC TILE, STONE AND THIN BRICK7.1 Adhesive Performance and Selection Criteria7.2 Types of Adhesives7.3 Methods of Adhesive - Cladding Installation

7.4 Cladding Installation Equipment and Procedures7.5 Grout and Sealant Joint Materials and Methods of Installation7.6 Post-installation Cleaning7.7 References

SECTION 8 INDUSTRY STANDARDS, BUILDING REGULATIONS AND....................145SPECIFICATIONS8.1 Background8.2 Building Codes and Regulations8.3 Industry Standards8.4 Guideline Specifications

8.5 References

IndexDirect Adhered Ceramic Tile, Stone, &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.6


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SECTION 9 QUALITY ASSURANCE, TESTING, INSPECTION .....................................153MAINTENANCE PROCEDURES9.1 Quality Assurance Procedures9.2 Preventative and Corrective Maintenance9.3 Protection and Sealing9.4 Non-destructive Testing

Visual InspectionComputer Modeling (Finite Element Analysis FEA)Tap (Acoustic Impact) TestingInfrared Imaging (Thermographic Scanning)Ultrasonic Pulse Velocity and Echo TestingMoisture Content TestingSalt Contamination Testing

9.5 Destructive TestingTensile Pull Strength TestingCore DrillingShear Bond Testing

9.6 Types, Causes and Remediation of DefectsStaining and WeatheringFluid MigrationEfflorescenceCrackingDelamination and Adhesive Bond FailureMovement Joint and Grout Failure

9.7 Case Study - Computer Modeling of Ceramic Tile CladdingFinite Element Analysis

9.8 References

SECTION 1O APPENDIX ................................................................................................19310.1 Frequently Asked Questions (FAQ)10.2 Resource Guide - Trade Organizations, Technical References10.3 About the Author

INDEX..............................................................................................................................201

IndexDirect Adhered Ceramic Tile, Stone, &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc. 7


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Photo: Balthazar Korab Project: Rainier Tower - Seattle, Washington 1977 Architect: Yamasaki & Assoc., Troy, MIDescription: Porcelain ceramic, mosaic tile over concave reinforced concrete structural coreDirect Adhered Ceramic Tile, Stone, &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.

SECTION 1INTRODUCTION

9


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SECTION 1 IntroductionDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.10

1.1 PREFACELATICRETE International, a manufacturer ofceramic tile, stone and brick masonryinstallation systems, has long recognizedthe need for a technical manual to provideguidelines and recommendations for thedesign, specification, and installation ofdirect adhered ceramic tile, stone, andthin brick cladding for exterior facades.Technical advances in materials,manufacturing, and construction methods

have expanded the role of this typeapplication ever since the development ofadhesive mortars in the 1950s. In keepingwith their position as an industry leader,LATICRETE International is publishing thisfirst edition of the DIRECT ADHEREDCERAMIC TILE, STONE and THIN BRICKFACADES Technical Design Manual tomake state-of-the-art information andtechnology available to architects,engineers, construction professionals, and

manufacturers in the ceramic tile, stoneand thin brick industries. It is also the goalof this publication to encourage new ideas,research, and building regulations for thepurpose of improving the future of thisconstruction technology and the ceramictile, stone and brick industries.

1.2 WHAT IS DIRECT ADHEREDCLADDING AND WHY USE

THIS TYPE OFCONSTRUCTION?

For the purposes of this manual, the termsdirect adhered facade, direct adheredexternal cladding and direct adheredexterior veneer are all usedinterchangeably. By definition, these termsrefer to an exterior wall or envelope of abuilding that is clad or faced on theexterior surface with a weather-resistant,non-combustible cladding material which

is directly adhered to a structural backingmaterial with an adhesive. The cladding isadhered in such a manner as to exertcommon action to the underlying wall

under load or applied forces. While thereare numerous materials that could be usedas an adhered cladding for a facade, in thismanual the term cladding refers to themost common materials used in this typeof construction; ceramic tile, natural stoneand agglomerates, and thin brick masonry.

Why use the direct adhered methodof cladding a building facade? There aremany advantages. Adhesive technology hasopened up an entire new world of aesthetic

and technical possibilities for cladding offacades. The direct adhered methodoffers the architect tremendous designflexibility provided by new materialswhich would otherwise be, or previouslywere, unsuitable as a cladding for facades,such as ceramic tile. The building ownerbenefits from the more efficient andenvironmentally sensitive use of materials,resulting from reduced weight, cost ofmaterial, and more efficient use of natural

resources. The building constructionprocess is made more efficient bylightweight, pre-finished materials, or frompre-fabricated wall components, which allreduce construction time, on-site laborcosts, and provide better quality assurance.

However, all these advantages of thedirect adhered method for claddingfacades can only be realized with a newapproach to the design and construction ofexterior walls. Design and construction

techniques must be adapted to the specificrequirements and behavior of constructionadhesive technology, as well as the uniqueattributes of ceramic tile, stone, and thinbrick cladding materials.

1.3 HISTORY OF CERAMIC TILESTONE AND THIN BRICKFACADES

Ceramic Tile

Ceramic tile has been used for centuriesas a decorative and functional cladding forthe exterior facades of buildings. Ceramictile development can be traced to 4000 B.C.

SECTION 1

INTRODUCTION


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SECTION 1 IntroductionDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc. 11

in Egypt. However, use of ceramic tile onwalls first appeared around 2700 B.C. whenit was used to decorate the graves ofpharaohs in Egypt. The earliest survivingexample of exterior ceramic (terra cotta) tile

cladding is the Dragon of Marduk sculpturefrom the Ishtar Gate in Mesopotamia datingto 604 B.C. (Figure 1.3-1) It was not until the13th century when wall tiling for exteriorwalls was established in the Middle East.All prominent buildings during this periodhad ceramic tile clad exterior walls. Theinfluence of Islamic architecture graduallyspread to Spain and Italy in the 16thcentury, where ceramic tile was usedextensively as an external cladding on

public buildings.Until recently, ceramic tile had beenused primarily on walls and buildingfacades because technology did not permitmechanically resistant and affordableproducts for floors and pavements. It is

ironic, that with the development of newceramic tile and adhesive technology, thebulk of modern production of ceramic tilesis now used on floors and interior walls,when for centuries ceramic tile was used as

a decorative and functional exteriorcladding material. The use of ceramic tile onmodern building facades has, until recently,been limited primarily as an isolateddecorative element, due to inconsistentperformance of past installations.

Natural Stone

Stone has been part of our buildingculture and heritage since the beginning of

human existence. Use of natural stone asan exterior cladding has been extensiveover the course of human history. This wasdue to mans ability to fabricate stone inblocks or sections of sufficient size andthickness to support its own weight

Figure 1.3-1 The Dragon of Marduk, Ishtar Gate, Mesopotamia, 604 B.C. 1

1Photo: Detroit Institute of Arts Founders Society


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SECTION 1 IntroductionDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.12

through stacking, either dry or withmortars.

With the development of lightweightstructural skeletons and curtain wallconstruction in the late 19th century, the

very weight and durability that made stoneso desirable, also made economicalfabrication and handling, difficult whichultimately slowed its development intothese new construction methods.

It was not until 1955 that the inventionof high quality synthetic diamonds andcarbide abrasives at the General ElectricCompany in the USA revolutionizedthe fabrication of thin stone to meet thecompetitive demands of construction

economy. The development of modernfabrication methods in the 1960s allowedrelatively thin slabs of stone (24 inches/50100mm thick) to be hung frombuilding exteriors using metal mechanicalanchors and curtain wall frames, followedby attachment to facades with adhesivetechnology. Further stone fabricationadvancements now allow thickness as lowas 1/4-3/16 inch (610mm).

In the 1950s, Henry M. Rothberg, an

engineer who later founded the companyLATICRETE International, invented aproduct and a new methodology thatwould make direct adhesive attachment ofceramic tile, natural stone, and thin brickon exterior building facades physically andeconomically feasible.2 This developmentrevolutionized both the ceramic tile andstone industries and has once againpopularized the application of ceramic tileand stone on facades (Figure 1.3-2 ).

Thin Brick Masonry

While the use of traditional clay brickmasonry has an extensive history, therecent introduction of thin bricktechnology was a direct result of thedevelopment of latex cement adhesivemortar and other types of constructionadhesive technology in the 1960s.

As we approach the next century, theconstruction industry is under extremeeconomic and social pressure to developnew and alternative technologies due tothe rapid depletion of our natural resourcesand the escalation of labor and material

costs for traditional construction. Newdevelopments in ceramic tile, stone andthin brick and adhesive technologies haveopened up an entire new world ofaesthetic and technical possibilities forexternal cladding of facades. Combinedwith sound design and constructionprinciples, direct adhered externalcladding is likely to become one of themost important building constructiontechnologies of the future.

1.4 SUMMARY OF MANUALCONTENT

Section 2 - Exterior Wall Concepts

A primer on the theory and terminologyof exterior wall construction. Types of

Figure 1.3-2 Direct Adhered Ceramic TileFacadePrefabricated panels on high riseconstruction, Los Angeles USA ,19603

2H.M. Rothberg The History of Latex in Portland

Cement Mortars, LATICRETE TDS 107.113Tishman 615 Building, Los Angeles, CA, USA glass mosaic tile on pre-fabricated panels, metalframe - cement plaster and metal lath substrate, 22stories


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SECTION 1 IntroductionDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc. 13

exterior wall structures and constructionare presented, together with commentaryon applicability to the direct adheredmethod for cladding facades.

Section 3 - Types of Direct AdheredWall Construction

Architectural details show typicalwall assembly configurations andrecommended design for direct adheredcladding. Examples of exterior wallconcepts presented in Section 2 aregraphically depicted with varioussubstrate/back-up wall materialcombinations. Details include design

recommendations for interface details suchas windows, roof parapets, movement jointsealants, flashings, and waterproofmembranes.

Section 4 - Structural and ArchitecturalConsiderations

Direct adhered cladding must bedesigned and constructed with careful

consideration of the complex interactionsthat occur between the other componentsof an exterior wall assembly. This sectionexplores issues such as the effect andprovision for structural movement, as wellas recommendations for interface witharchitectural elements such as windows.

Section 5 - Substrates

The selection and preparation of a

substrate is one of the most critical stepsin design and construction of directadhered cladding. Suitability andcompatibility of the most commonsubstrates is covered, together withcomprehensive recommendations forpreparation such as evaluation of levelnessand plumb tolerances, surface defects, andthe effect of climatic and site conditions onsubstrates.

Section 6 - Selection of ExteriorCladding Material

Investigation and selection of the propertype of cladding is an important designdecision. Detailed criteria for the

assessment and selection of ceramic tile,stone, and thin brick are presented,together with important ancillaryconsiderations such as color/temperatureand moisture sensitivity of natural stoneand man-made stone agglomerates.

Section 7 - Installation Materials andMethods - Adhesion and Grouting ofCeramic Tile, Stone and Thin BrickCladding

This section covers the entire range ofinstallation and construction issues, fromselection criteria for adhesives, to the typesof installation procedures and equipmentrequired for the direct adhered method ofconstruction.

Section 8 - Industry Standards, BuildingCodes and Specifications

Detailed information on applicableindustry standards for both ceramic tileadhesives and direct adhered externalcladding is provided. Model buildingcodes, including detailed excerpts fromselected codes, are included. A chart liststhe most common codes and standardsfrom around the world that are applicableto direct adhered cladding.

Section 9 - Quality Assurance, Testing,Inspection and MaintenanceProcedures

Recommendations for planning andimplementation of a quality assuranceprogram are outlined. Cleaning, protection,and preventative maintenance proceduresare presented, along with design andconstruction diagnostic test methods. Thissection includes information on types,causes, and remediation of defects.


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1.5 CASE STUDY


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SECTION 2EXTERIOR WALL CONCEPTS

Photo: Project: Portland Building, Portland, Oregon 1982, Architect: Michael Graves & Associates, Princeton, NJDescription: Gail 10 x 10 inch (20 x 20mm) glazed brickplate and glazed ceramic tileDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.


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2.1 FUNCTION OF EXTERIORWALLS

The primary purpose of an exterior wallassembly is to separate the externalenvironment from the internal environment.To perform this function, the exterior wallmust act simultaneously as a restraint, abarrier and a selective filter to control acomplex, often conflicting series of forcesand occurrences.

Functions of Exterior Walls

Wind pressure and seismic forceresistance

Thermal and moisture movementresistance

Energy conservation and control of heatflow between interior-exterior

Rain penetration resistance and control Water vapor migration and condensation

control

Sound transmission resistance Fire resistance and containment Daylight transmission to the interior

environment; vision to exterior Air transmission between and within the

interior-exterior Passage of occupants

2.2 TYPES OF EXTERIOR WALLS

Exterior wall assemblies are generallyclassified in three broad categories of walltype structures according to the methodused to support the loads or forcesimposed on the building, and the methodof structural attachment to the buildingsinternal components.

Types of Exterior Wall Structures

Bearing walls Non-bearing walls Curtain walls

Bearing Wall

A bearing wall is defined as a wallwhich supports both its own weight, and

the weight all the other loads and forcesacting on the building, including theweight of the floors, roof, occupants, andequipment. The bearing wall is supportedby the buildings foundation in the ground.It is the primary structural support of abuilding and an integral component of theother structural components such as thefloors and roof. With the advent of modernstructural (skeletal) framing systems, thiswall type is typically used on buildings less

than three stories high.

Non-Bearing Wall

This type of wall only supports its ownweight, and is supported directly on thefoundation in the ground. Non-bearingwalls are also limited to low riseconstruction.

Curtain WallThis is broad category for a type of

exterior wall assembly which supports onlyits own weight and no roof or floor loads(similar to non-bearing wall types), but issecured and supported by the structuralframe of a building. The curtain walltransmits all loads imposed on it (lateralwind/seismic and gravity loads) directly tothe buildings structural frame. This is themost common wall type, especially inmulti-story construction.

2. 3 TYPES OF EXTERIOR WALLCONSTRUCTION

Within each category of wall structures,there are also three types of wallconstruction configurations. Each type ofwall construction differs primarily by themethod employed to prevent air, vapor,and water infiltration. Secondarydifferences are the methods and materialsused to control other forces, such as heatflow or fire resistance.

SECTION 2 Exterior Wall ConceptsDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.16

SECTION 2

EXTERIOR WALL CONCEPTS


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Types of Exterior Wall Construction

Barrier wall Cavity wall Pressure-equalized rainscreen wall

Bearing, non-bearing, and curtain wallstructures can employ any of the abovetypes of wall construction, although certaintypes of wall structures are more adaptableto certain types of wall construction.

Barrier Wall

Historically, we have relied on this typeof wall for most of human history. Thepurpose of a traditional barrier wall design isto provide a relatively impenetrable barrier

against water and air infiltration, relyingprimarily on massive walls to absorb,dissipate, and evaporate moisture slowly.The mass of the wall also controls otherforces such as sound, fire, and heat flowquite efficiently. Openings or vulnerable

joints are protected from water infiltrationby roof overhangs, window setbacks, dripedges, and other types of physical shields.

Today, constructing a traditional barrierwall with massive walls and a complex

configuration is cost prohibitive. Instead,economics of modern construction requirethat barrier wall construction be thinand lightweight. Modern barrier wallconstruction relies on impermeablecladding materials and completely sealed

joints between exterior wall assemblycomponents to resist all water penetration.While a barrier wall design typically hasthe lowest initial cost than other exteriorwall configurations, the lower initial cost is

offset by higher lifecycle costs, due tohigher maintenance costs and lowerexpected life span caused by moreaccelerated rates of deterioration.However, with the pace of aesthetic andtechnological change in our culture,reduced life cycles for certain types ofbuildings have become acceptable.

A direct adhered ceramic tile, stone, orthin brick barrier wall facade does havelimitations that may increase frequency of

maintenance and decrease useful life. Stoneand thin brick cladding materials will allowvarying degrees of water penetrationdirectly through the surface. Water

penetration may also occur through hairlinecracks in naturally fragile stone that, whilenot affecting safety, can occur from normalstructural, thermal, and moisture movementin the building. Similarly, hairline cracks in

joints between the ceramic tile, stone,or thin brick that are grouted withcementitious material will also allow waterpenetration. While ceramic tile suitable forexterior walls can be impermeable, thecementitious joints between tiles will bepermeable, unless they are filled withepoxy grout or silicone/ polyurethanesealants. In an attempt to prevent waterpenetration with impermeable joint fillers,the following new problems may be

created:1) it is impossible to achieve a 100%

seal against water with a field appliedsealant or epoxy grout over thousands oflineal feet/meters of joints.

2) a totally impermeable exterior wallmay perform well in warm, humidclimates; but in colder climates, watervapor from the interior of the building mayget trapped within the wall and condense,causing internal deterioration of the wall.

3) sealant joints require frequentmaintenance and replacement.

Cavity Wall

This type of wall construction consistsof an inner and outer layer of wallcomponents separated by an air cavity.Recognizing the difficulty of achieving a100 percent effective water barrier, a cavitywall is designed to allow a certain amountof water to penetrate the outer layer intothe cavity. Water cannot bridge the aircavity easily, so it drops by gravity and isthen controlled and directed by properlydesigned drainage outlets back to theexterior surface of the wall.

Pressure Equalization

This type of wall construction is a moresophisticated type of cavity wall wherespecially placed and sized openings in theexterior cladding allow outside air topenetrate the cavity and reach the samepressure as the outside air, thus the term

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pressure equalize. This type of wallconstruction reduces the internal wallcavity pressure differential (Figure 2.3-1).A pressure differential could cause waterand vapor to be forced and suctioned in

either direction across the cavity, resultingin leakage and deterioration. The internalwall cavity is normally at differentpressures due to wind flow over theexterior facade, the stack rising effect ofair flow in a building, and HVAC(heating/ventilating) system pressurizationand imbalance.

To allow proper air pressure transfer, theinner layer of wall construction must beairtight. This is achieved by installation of

an air retarder on the exterior surface of theinner layer of the cavity wall assembly.

Future Exterior Wall Technology -The Dynamic Buffer Zone

Studies have shown that moistureaccumulation in wall cavities occurs moreoften from the water vapor migrationand build-up of condensation than fromrain or snow penetration. One studyhas demonstrated that in one month,approximately 31 pounds/15 kg of watercould leak by air leakage and resultantcondensation through an electrical outletwith a net open area of 1 inch2/6.5 cm2

and an interior-exterior air pressuredifference equivalent to a 9.3 mph/15 km/hour wind.4

The mechanism behind moisturecondensation is the exfiltration of humidindoor air in cold climates, and to a lesserdegree, the infiltration of humid air inwarm climates to the cool internal wallcavity. Though vapor barriers and the moresophisticated air barriers provided byventilated or pressurized rain screen walldesigns have greatly improved air andwater vapor resistance of exterior walls, aperfect seal is not feasible. Water vaporcondensation will continue to occur inbuildings with moderate humidity levels incold climates, and in air conditionedbuildings in warm, humid climates.

In direct adhered cladding systems,many of the problems that we associatewith apparent rain penetration areactually caused by accumulation of

condensation. This internal wall moisturenot only causes water leakage andstaining, but is often responsible forproblems such as efflorescence, mildewodors, diminished insulation value,corrosion of metal components, andreduced strength, or even failure ofadhesives and membranes.

Research and full scale testing was

recently resurrected for an exterior wallconcept known as the Dynamic BufferZone (DBZ)5, which was first proposed inthe 1960s. The DBZ concept, while fairlysophisticated, has been demonstrated tosignificantly reduce or even eliminatemoisture in the internal cavities of exteriorwalls by mechanically pumping dryoutdoor air into the wall cavities inbuildings located in cold climates. Thus far,this concept has not been tested in warm

humid climates, but the technology haspromise to also solve similar problemsunique to warm humid climates, such ascondensation and mildew growth/odorsfacilitated by air-conditioning. The DBZtechnology works through pressurization ofthe exterior wall cavity using partially

SECTION 2 Exterior Wall ConceptsDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.18

Figure 2.3-1 Typical cavity wall air pressuredifferentials

4

Quirouette, R.L., The Difference Between a VaporBarrier and an Air Barrier, BPN 54, NRC Canada,19855Quirouette, R.L.,The Dynamic Buffer Zone, TheConstruction Specifier, August 1997


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heated outdoor air in cold climates. A DBZwall system is designed so that the wallcavity pressure is above the indoor roompressure, thus limiting passage of indoorhumidity by air leakage. The most

significant challenge in the practicalapplication of the Dynamic Buffer Zoneconcept is not necessarily the cost (muchof the infrastructure and equipment alreadyexists in modern commercial buildings);the challenge lies in the extensive level ofdetail and coordination of mechanicalengineering and architectural disciplines,and the correlating trades on theconstruction site.

2.4 REFERENCES

1. Quirouette, Rick, Dynamic BufferZone, Construction SpecifierMagazine, Aug.1997

2. Persily, Andrew, Envelope Design

Guidelines for Federal OfficeBuildings, Progressive ArchitectureMagazine, March,1992

3. Robinson, G. & Baker, M.C., WindDriven Rain and Buildings, NRCC14792 National Research Council,Canada,1975

4. Canadian Building Digest 40, NationalResearch Council, Canada, RainPenetration and its Control, 1963

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SECTION 3TYPES OF DIRECT ADHERED WALLCONSTRUCTION

Photo: Project-Hotel Nikko, San Francisco, CA USA Architect: Takanaka Associates, Tokyo, JapanDescription: 2 x 2 inch (50 x 50mm) porcelain tile adhered by the negative cast method on precast concrete panelsDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc. 21


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SECTION 3 Types of Direct Adhered Wall ConstructionDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.22

3.0 ON-SITE CONSTRUCTION

3.1 CONCRETE MASONRY UNITBACK-UP WALLS

Concrete block masonry units (CMU) arethe preferred back-up wall system forinstallation of direct adhered cladding inbuildings where a long service life andmaximum durability is desired. CMU wallthickness must be calculated basedon engineering analysis as required by

building codes. However, the empirical ruleof a height to thickness ratio of 18 remainsa good guide for preliminary selection ofwall thickness. Walls should be a minimumthickness of 8 inches (200mm).

CMU walls usually require vertical andhorizontal reinforcing in order to satisfyseismic requirements. Joint reinforcingshould be used at every second horizontalbed joint.

Barrier Concrete Masonry WallsSingle wythe CMU back-up walls are

barrier walls and therefore must bewaterproofed, even if they are clad with arelatively impermeable cladding. Every

joint between the ceramic tile, stone orthin brick cladding is a potential source ofwater penetration. Cement or latex cementleveling plasters (renders) or parge (skim)coats may provide adequate protection inextremely dry climates but water will

penetrate during prolonged periods of rainand cause either leakage, deterioration ofunderlying materials, or sub-surfaceefflorescence which can result in adhesivebond failure.

Through-wall flashing and weep holescan be provided in the CMU at the bottomof the wall at windows splitting the wallinto two thin wythes at the flashing.

Cavity Concrete Masonry Walls

The outside face of the internal wythe ofCMU back-up walls should bedamproofed, as cavity walls are designedwith the anticipation of water penetration.

Cavity walls should have an unobstructedair space between the inner and outerwythes. The air space prevents infiltratedwater from bridging to the inner wall, andcan be designed to equalize outside andcavity air pressure to prevent water frombeing driven across the air space. Watercan then be collected and directed back tothe exterior surface of the cladding (seeSection 2 - Pressure Equalization).

The recommended width of a cavity is 2

inches (50mm), and should not be lessthan 1 1/2 inches (32mm) or greater than 4inches (100mm). If rigid insulation is usedin the cavity in cold climates, a 2-inch(50mm) air space should be provided fromthe face of the insulation.

Weep holes should be placed at thebottom of each floor level, bottom of walls,at window sills, and any other locationswhere flashing is provided. Weep holes arenormally spaced at 24 inches (600mm),

but no greater than 32 inches (800mm) oncenter, and located where the verticaljoints of both the CMU and externalcladding align. The cavity base should beprovided with drainage material, such asgravel or plastic drain fabric to preventmortar droppings from blocking drainage.

Flashings (see Section 4) are used tocollect and direct water which hasinfiltrated the cavity back to the exteriorthrough weep holes. Flashings must be

terminated in a horizontal CMU joint, andmust be turned up a the ends of windowsills or other horizontal terminations toform a dam, otherwise water will travellaterally and leak at the ends of theflashing. At the face of the externalcladding, flashing should be terminated ina rigid sheet metal drip edge to direct anywater away from the face of the cladding. Ifflexible sheet or fluid applied flashings areused, they need to be bonded to a rigid

metal drip edge.The external CMU wythe and externalcladding are anchored to the back-up CMUwall with galvanized steel wall ties typicallyspaced 16 inches (400mm) on center

SECTION 3

TYPES OF DIRECT ADHERED WALL CONSTRUCTION


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vertically and horizontally. Anchors requireflexible connections in order to allow formisalignment of the internal/external CMUcoursing, and to permit differentialmovement both within the CMU wall, and

between the external cladding-CMU walland the internal back-up wall and structuralframe.

3.2 CLAY (BRICK) MASONRYBACK-UP WALLS

Clay brick masonry back-up walls, whetherdesigned as barrier or cavity walls, aregenerally constructed using the sameprinciples and design techniques asconcrete masonry back-up walls.

However, there is one importantdifference between the two materials. Claybrick will expand permanently with age asa result of moisture absorption. When abrick is fired during the manufacturingprocess, all the moisture has beenremoved, and clay brick will graduallyincrease in volume from the originalmanufactured dimensions. (See Section6.4)

Consequently, clay brick masonry back-

up walls must make provision for expansion.This is particularly important where claybrick is used in a barrier wall configurationto infill between structural concrete frames;restrainment of expansion can cause theback-up wall to bow outwards.

3.3 LIGHT GAUGE STEEL METALSTUD, BACK-UP WALLS

Light gauge metal (galvanized steel) studs

are commonly used as a back-up wallstructure for directed adhered cladding.Metal stud back-up walls are onlyrecommended in buildings with ananticipated facade service life of 30 years.

The metal stud frame can employ avariety of sheathings, the type of sheathingdependent on whether the wall is barrierwall requiring direct adhesion of thecladding material, or a cavity wall wherethe sheathing type does not affect

adhesion. Metal stud walls can also beused for both pre-fabrication of panels, orconstruction in-place.

Metal stud size and gauge are selectedbased on known structural properties

required to resist live and dead loads. Thepredominant live load is wind, thereforestiffness usually controls size of metal studs.Empirical experience has shown that 6 inch(150mm) wide, 16 gage studs spaced

16 inches (400mm) on center areappropriate for most applications.However, engineering calculations mayshow that other widths and gauges arerequired. Deflection (measure of stiffness)of metal stud back-up wall construction forexterior facades should be limited to 1/600of the unsupported span of the wall underlive (wind) loads. While this is the currentallowable deflection for metal stud back-upwalls, some studies on conventional

masonry veneer cavity walls have showncracking can occur on walls that havesignificantly less deflection. There havebeen no definitive studies conducted onmetal stud barrier walls used in directadhered cladding, but empirical evidenceindicates that the composite action of rigidcladding materials, high strength adhesives,and proper specification of sheathingmaterial and attachment method to metalstuds does create a more rigid diaphragm

compared to a metal stud back-up wallseparated by a cavity.Metal stud framing typically requires

lateral bracing to, or integration within thestructural steel frame of a building. Bracingis dependent on the configuration andunsupported length of the stud frame.Empirical experience has again proven thatintegration within the structural steelsystem not only provides a stiffer metalstud wall by reducing the unbraced lengths

of studs, but also improves accuracy andreduces errors by providing an establishedframework where studs are used as infillrather than the entire framework.

There are a wide variety of sheathingmaterials to choose from for metal studwalls, ranging from low cost exteriorgypsum sheathing or plywood for cavitywall sheathing, to cement backer board, orlath and cement plaster for barrier wallsrequiring direct adhesion of the cladding

material.Gypsum sheathings historically have notbeen a very durable material for cavitywalls, although new gypsum basedsheathings with fiberglass facings and

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SECTION 3 Types of Direct Adhered Wall ConstructionDirect Adhered Ceramic Tile, Stone, &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.24

silicone impregnated cores have improvedperformance.

Cement plaster is an ideal sheathing formetal stud back-up walls. This sheathingprovides a seamless substrate with no

exposed fasteners, resulting in good waterand corrosion resistance. The integralreinforcement also provides necessarystiffness, resistance to shrinkage cracking,and positive imbedded attachment pointsfor anchorage to the metal stud frame. Theattachment of the reinforcing in a cementplaster sheathing and resulting shear andpull-out resistance of the fasteners withinthe sheathing material is superior to that ofpre-fabricated board sheathings such as

gypsum or cement backer unit boards(CBU). This factor is important in moreextreme climates where there is moresignificant thermal and moisture movementwhich can affect sheathings that are poorlyfastened or have low shear or pull-outresistance to fasteners.

Cement backer unit boards (CBU), fibercement and calcium silicate boards areother choices for metal stud back-up wallsrequiring direct adhesion of the cladding

material. CBU board is pre-fabricated,and provides an efficient, cost effectivecementitious substrate for adhesion ofcladding materials. While CBU istechnically water resistant, it requireswaterproofing, as the minimal thicknessand corrosion potential of screwattachments increase the possibility forminor cracking, leaks, deterioration, anddefects such as efflorescence. Fiber cementboards can be sensitive to moisture, and

require waterproofing on both sides to resistdimensional instability that may be causedby both infiltrated rain water orcondensation on the back side of the board.

There are proprietary direct adheredwall systems which employ corrugatedsteel decking as a sheathing and substratefor cladding adhered with special structuralsilicone adhesives. Because these systemsemploy spot bonding rather than acontinuous layer of adhesive, the

combination of open space behind thecladding and the corrugation of the steeldecking provides a cavity for drainage andventilation. This cavity anticipates waterpenetration, and re-directs water back to

the exterior wall surface. However, theunderlying metal decking and framing aresubject to corrosion facilitated by abrasionof galvanized coatings during construction.Leakage may also occur due the difficulty

in waterproofing the steel and multipleconnections/penetrations. Corrugated steelsheathing cavity walls have a limitedservice life similar to that of barrier walls.

Generally, the light weight and minimalthickness of most sheathing materials formetal stud barrier back-up walls makethem more susceptible to differentialstructural movement and dimensionalinstability from thermal and moistureexposure. Therefore, careful engineering

analysis of cladding-adhesive-sheathingmaterial compatibility, and analysis of theanticipated behavior of the sheathing andits attachment are critically important.

3.4 CAST-IN-PLACEREINFORCED CONCRETEBACK-UP WALLS

Cast-in-place concrete is one of the mostcommon back-up wall materials for directadhered external cladding. However, it is

unusual that an entire facade back-up wallconstruction will be concrete; typically onlythe face of the structure or walls at the baseof the building are concrete. Cast-in-placeconcrete is only economical in barrier walltype of construction, and resists waterpenetration by virtue of mass and density.However, it is still recommended towaterproof concrete, as saturation withwater can cause efflorescence.

There are several other important

considerations unique to vertically cast-in-place concrete used as a back-up wall forexternal cladding (see Section 5 fordetailed information):

form release agents surface defects dimensional change and cracking caused

by shrinkage

3.5 PRE-FABRICATED PANELCONSTRUCTION

3.6 PRE-CAST CONCRETE WALLPANELS

Ceramic tile, stone, and thin brick clad pre-cast concrete panels combine durability


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and tremendous design flexibility with thestrength and economy of pre-cast concrete.The primary advantage of this type of back-up wall construction is the economy of pre-fabricated, panelized construction.

Prefabrication permits construction ofpanels well in advance of the normalsequencing of on-site construction of abuildings exterior wall. Once the properstage in the sequence of construction isreached, panels can be erected quickly,without weather or scaffolding erectiondelays. Pre-cast concrete also allows morestringent quality control afforded by plantproduction of both the batching andcasting of the concrete, as well as the

installation of the cladding material.The considerations for clad pre-castconcrete panels are generally the same asthose for un-faced panels, with twoexceptions; the method of installation forthe cladding material, and investigation ofdifferential thermal and moisturemovement between the pre-cast concreteand the cladding material.

Pre-Cast Concrete Panels - Negative

and Positive Cast Methods

There are two methods for installationof cladding on pre-cast concrete panels;the negative and positive cast methods.Negative cast panels involve the casting ofthe concrete and bonding of the claddingin one step. The cladding material isplaced face down over the face of thepanel mold; joint width and configurationare typically controlled by a grid to insureproper location, uniform jointing andsecure fit during the casting operation.

Joints are typically cast recessed, andpointed or grouted after the panel is curedand removed from the mold. This methodrequires the use of a cladding with adovetail or keyback configuration on theback in order to provide mechanicallocking action between the cladding andthe concrete. The mechanical bondstrength afforded by the integral locking ofthe concrete to the back is oftenaugmented by the use of latex Portlandcement slurry bond coats or polymericbonding agents just prior to casting of thepanel.

Positive cast panels are prefabricated intwo separate processes. The pre-cast panelis cast, cured, and removed from the mold,and the cladding material is then installedusing an adhesive in the production plant.

Installation of the cladding after erectionand attachment to the structure on-site isviable, but this sequencing defeats the goalof economy and quality control providedby prefabrication.

Pre-Cast Concrete Panels - DifferentialMovement (Internal to Panel)

Differences in the physical characteristicsof the pre-cast concrete and the claddingmaterial make this type of back-upconstruction more susceptible to problemsof panel bowing or excessive shear stress atthe adhesive interface.

Bowing of panels can occur fromseveral mechanisms. In negative castpanels, the concrete shrinks as it hydratesand excess water evaporates. The cladding,being dimensionally stable, can restrain theshrinkage of the concrete. The result iscompressive stress in the cladding, andtensile stress at the adhesive interface, withthe potential for outward bowing of thecladding surface.

The best techniques in preventing panelbowing is to control the concrete shrinkageand to provide the proper ratio of crosssectional area to stiffness (modulus ofelasticity) of the panel. Avoid flat panelsless than 56 inches (125150mm) thick;panels as thin as 4 inches (100mm) can beused in panels with small areas, or inpanels where stiffness is increased byconfiguration or composite action with athick cladding material. Concrete mixdesign and curing conditions can beadjusted to minimize shrinkage.

Several other techniques, such as theamount, location, and type of (prestressing)reinforcement, or introduction of camberto the panel, have been developed tocompensate for possible bowing caused byshrinkage.

Differential movement caused bydifferent coefficients of thermal expansionbetween the cladding and the concrete canalso result in panel bowing. The optimumcondition is for the concrete to have a

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from flex anchors by their size,configuration, and connection orientationto the GFRC. It is very important toconsider the additional weight of thecladding material during the design and

engineering of a GFRC panel; you cannotinstall direct adhered cladding using thepositive method unless the panel wasengineered specifically for that purpose.

Properly engineered and constructedGFRC panels have extremely high strengthand good physical characteristics,However, due to the thin section employedin GFRC panels, differential thermal andmoisture movement can cause panelbowing, resulting in cracking. Because

GFRC expands and contracts from wet-drycycling, the adhesion of a cladding canresult in a different rate of moisture gain orloss between the front and back of thepanel and induce bowing stress. Therefore,careful attention to detailing to preventrain infiltration and condensation withinthe wall (see Section 4) are important.Similarly, cladding materials withincompatible coefficients of thermalmovement can induce stress. So thermal

and moisture movement compatibility withcladding is important, as are low modulusadhesives and movement joints.

3.7 LIST OF ARCHITECTURALDETAILS (SEE PAGES 2765)

3.7-1 to 3.7-7 Barrier wall, concretemasonry back-up wall, continuouswaterproof membrane3.7-7 to 3.7-14 Barrier wall, -concrete

masonry back-up wall, membrane flashing3.7-15 to 3.7-17 Barrier wall, metal studback-up with cement board or plaster3.7-18 to 3.7-20 Cavity wall, metal studback-up with cement board or plaster3.7-21 to 3.7-23 Barrier wall, precastconcrete panels3.7-24 to 3.7-30 Cavity wall, double wytheconcrete masonry3.7-31 to 3.7-33 Cavity wall, concretemasonry and metal stud back-up wall

3.7-34 to 3.7-36 Cavity wall, epoxy spotbonding3.7-37 to 3.7-39 Barrier wall, GFRC panel


rate of thermal expansion that closelyapproximates that of the cladding. Thethermal coefficient of expansion of concretecan be modified slightly by adjustment ofaggregate type, size and proportion to

provide compatibility with the cladding andminimize differential movement undertemperature changes.

Pre-cast Glass Fiber ReinforcedConcrete Wall Panels (GFRC)

Pre-cast glass fiber reinforced concrete(GFRC) is the term applied to a materialwhich is fabricated from a cement-aggregate slurry and reinforced with alkali-resistant glass fibers. Mix composition

and types of applications vary, but forinstallation of direct adhered cladding,GFRC panel consist of mix which contains5% by weight of glass fibers combined witha Portland cement-sand slurry which isspray applied onto a form. The form maycontain a cladding material (negative castmethod) to which a bond coat of latexPortland cement is applied just prior toapplication of the GFRC material, or thepanel is cast, cured and removed from the

form for subsequent application of acladding material in a separate process(positive cast method). A single skin GFRCpanel is the most common type of panelconstruction. This type of panel has athickness of approximately 1/2 inch (12mm),however it is recommended to increase thethickness of the GFRC panel, toapproximately 1 inch (25mm) to reduceand better resist differential movementstress. GFRC panels rely on a structural

backing or stiffener of a steel studframework. The steel frame is commonlyseparated from the GFRC by an air spaceand attached to the GFRC by means of 1/4inch (6mm) diameter rods called flexanchors, which are imbedded into theGFRC and welded to the framework. Theseanchors, while rigidly attached, haveflexibility inherent by diameter andorientation of the rods, which allow somepanel movement to accommodate thermal

and moisture movement. Heavier panels, orthose requiring seismic bracing, alsorequire additional anchors known as gravityor seismic anchors, and are differentiated


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Figure 3.7-1 Architectural Details of Barrier Wall - Concrete masonry unit backup with continuouswaterproof membrane



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Figure 3.7-8 Architectural Details of Barrier Wall - Concrete masonry unit backup with membraneflashing


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Figure 3.7-15 Architectural Details of Barrier Wall - Barrier Wall - Light gauge steel (metal stud) withcement backer board (CBU) or cement plaster backup


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Figure 3.7-16 Architectural Details of Barrier Wall - Light gauge steel (metal stud) with cementbacker board (CBU) or cement paster backup


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Figure 3.7-18 Architectural Details of Cavity Wall -- Light gauge steel (metal stud and cement boardback-up


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Figure 3.7-19 Architectural Details of Cavity Wall - Light gauge steel (metal stud and cement boardback-up


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Figure 3.7-20 Architectural Details of Cavity Wall - Light gauge steel (metal stud and cement boardback-up


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Figure 3.7-21 Architectural Details of Barrier Wall - Negative cast pre-cast concrete panels


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Figure 3.7-24 Architectural Details of Cavity Wall - Concrete masonry back-up


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Figure 3.7-32 Architectural Details of Cavity Wall - Concrete masonry unit with steel stud backup


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Figure 3.7-33 Architectural Details of Cavity Wall - Concrete masonry unit with steel stud backup


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Figure 3.7-34 Architectural Details of Cavity Wall - Epoxy spot bonding over concrete masonryback-up


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Figure 3.7-35 Architectural Details of Cavity Wall - Epoxy spot bonding over concrete masonryback-up


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Figure 3.7-37 Architectural Details of Barrier Wall - GFRC pre-cast concrete panels - negative castmethod


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3.8 CASE STUDYCERAMIC TILE CLADPRE-CAST CONCRETE

City Hospital features ultra efficient

precast concrete wall system using therain-screen principle

Saskatoon City Hospital, winner of theprestigious PCI Design Award, hasreceived much praise for the appearanceand technical superiority of its precastconcrete wall system. The precast panelsare clad with ceramic tile, a first inSaskatchewan, Canada. They also featurethe proven rain-screen principle. Thedetailing of the precast cladding materialis very well handled. Some toughchallenges were overcome in this rathersophisticated panel system, said thePrecast/Prestressed Concrete Institute

judges when they presented the 1992Design Award to the hospitals architects.

The Project

The 492-bed facility provides a communitygeneral hospital for Saskatoon, and a major

referral center for all of northernSaskatchewan.In choosing precast wall panels, the

architects were seeking a high performancewall with an effective and durable air

Figure 3.8-1 Saskatoon City Hospital - Ceramic tile clad pre-cast concrete panels

barrier, high insulation value and minimalthermal breaks. They wanted factorymanufacture of the system to obtainsuperior quality and rapid enclosure of thehospital during construction. This type of

high quality wall system is suitable for allbuildings, but particularly those with highhumidity in severe climates.

Testimonial

Super, it looks great - the cladding willreally offset the surrounding landscape,said the Executive Director of the hospital,Mr. Elmer Schwartz. The preferred profileof the exterior wall could not have beeneffectively achieved with any system

other than the precast concrete panels,explained Gerry Wilson of City HospitalArchitects Group, the buildings designers.The appearance of the ceramic tile precastconcrete panels has been well received bymembers of the design team, the ownerand the general public, he added.

The Ideal Wall

The hospital wall is a precast concrete

sandwich panel incorporating insulationand a rain-screen, with a ceramic tile finishon the exterior. This is how a high-performance wall was described in a reportby City Hospital Architects Group:


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Figure 3.8-2 Saskatoon City Hospital - Ceramic tile clad pre-cast concrete panels

Figure 3.8-3 Wall Sections - Saskatoon City Hospital - Ceramic tile clad pre-cast concrete panelswith pressure-equalized rain-screen cavity


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Technically, a quality wall has anexterior skin which can expand andcontract in various conditions. Behind thisskin is an air space which is maintained atexterior air pressures (positive and

negative), consequently excluding waterpenetration through the facade due to airpressure differentials. This technique iscommonly referred to as a rain-screen. Thenext element adjacent to the air space isthe insulation which, in addition to itsenvelope function, protects the buildingstructure and any structure supporting theouter skin, from thermal stresses. Anair/vapor barrier can be applied on eitherside of the system supporting the outer skin

(or be within the system). The connectionsbetween the outer skin and the innersupporting structure should be minimal.Connections between the total wall system

and the building should not pierce theair/vapor barrier and should be thermallyprotected.

3.9 REFERENCES

1. PCI Design Handbook, Precast andPrestressed Concrete Institute, 1992

2. Prestressed Concrete Institute,Recommended Practice for Glass FiberReinforced Concrete Panels, 1987

3. Look-alike Towers are Lightweight,Ceramic Tile Clad GFRC Panels,Engineering News Record, 1987

4. Cowie, J.W., Failure of Brick MasonryVeneer Walls, Masonry ConstructionMagazine, Feb. 1990

5. Arumala, J.O., Performance Evaluationof Veneer with Steel Stud Back-up,Clemson University, Apr. 1982


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Photo: Project-Office Building, SingaporeDescription: Marble cladding over cement render and reinforced concreteDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc. 69

SECTION 4

STRUCTURAL AND ARCHITECTURAL

CONSIDERATIONS


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SECTION 4 Architectural & Structural ConsiderationsDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc.70

4.0 GENERAL BACKGROUNDImportant structural and architecturalconsiderations in the design of directadhered cladding are:

Compatibility of the bonding adhesivewith both the cladding material and thesubstrate

Dimensional stability of the claddingmaterial and substrate

Thermal and moisture expansioncompatibility between the claddingmaterial and the substrate

Differential movement capability ofbonding adhesive

4.1 TYPES OF STRUCTURAL

MOVEMENT

The structural frames of modern buildingsare considerably more vulnerable tomovement than traditional massive masonryor concrete structures. This trend is not onlydictated by economics, but also thedevelopment of new materials and methodsthat are stronger, lightweight, and capable ofspanning great distances and heights.

While modern structural frames aresafe, they are designed to be more flexibleand typically provide less resistance tomovement. It is essential that directadhered external cladding be designed andconstructed to accommodate all typesof structural movement. Direct adheredexternal cladding differs from mechanicallyanchored cladding primarily becausestructural movement can be transmittedthrough the direct adhesive connection,

accumulate, and then exert stress on thecladding, resulting in cracking, buckling,or crushing of both the cladding or otherwall components.

Most of the structural movement in adirect adhered facade is controlled by theunderlying wall components and theirconnection to the buildings structuralframe; the adhered cladding is a non-

structural finish. However both theadhesive and the perimeter interfaces withthe cladding must be designed to furthercontrol and minimize reflection ofdifferential structural movement.

The most difficult aspect of designingan exterior wall system is that structuralmovement is somewhat unpredictableand indeterminate. Building movements

are individually quantifiable throughmathematical calculations. However,building movements are dynamic; theyare constantly changing and notnecessarily simultaneous. As a result, theexact magnitude of resulting stresses frombuilding movement can be difficult topredict. Fortunately, the structural theoryused in most building codes dictates use ofworst case conditions; movements are

considered to act simultaneously, and be ofthe highest possible magnitude in order toprovide a safety factor for the most extremeconditions.

Types of Structural Movement

Live loads (wind, seismic) and deadloads (gravity)

Thermal movement

Drying shrinkage* Moisture expansion* Elastic deformation under initial loads Creep of concrete under sustained load* Differential settlement

Live Loads

Lateral forces due to anticipated gravity,wind or seismic loads must be analyzed to

determine the required tensile and shearbond strength of adhesive mortars to resistthese forces.

For non-load bearing curtain walls,wind loading is typically the dominantstructural load which a wall must be

SECTION 4

STRUCTURAL AND ARCHITECTURAL

CONSIDERATIONS

*denotes types of movement in concrete or woodstructural frames only


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engineered to resist. The wall must beengineered to have not only sufficientstrength to resist the positive and negative(suction) wind pressures, but also sufficientstiffness so that the direct adhered claddingmaterial does not crack under high windloads. Deflection or stiffness of back-up

wall construction should be limited to1/600 of the unsupported span of the wallunder wind loads.

In regions with seismic activity, theshearing force exerted by seismic activity isby far the most extreme force that anadhesive bond must be able to withstand.The shear stress exerted by an earthquakeof a magnitude of 7 on the Richter Scale is

approximately 215 psi or 15 kg/cm 2, sothis value is considered the minimum safeshear bond strength of the cladding,adhesive and substrate interfaces.

The shearing forces induced by thermalmovement are similar to seismic activity inthat they are typically far greater than thedead load (weight) of the claddingmaterial.

Wind and seismic forces can also cause

lateral building movement called drift. Thistype of movement is characterized by theswaying of a building from wind or seismicactivity, and is the type of movement thatcan be controlled and isolated withmovement joints. While seismic and windmovement joints are typically a structuralengineering function of the underlyingstructure and back-up wall construction, it

is critical that this movement capabilityextend through to the leveling andadhesive mortars, as well as to the externalcladding surface and interfaces with otherwall components.

Building codes typically limit drift ordisplacement of a story relative to theadjacent story to .005 times the storyheight. For example, a 12 foot (4 m) singlestory height could have maximum

allowable drift due to design wind load of.005 x 12 ft (4m) x 12 in/ft (1000 mm/m) =3/4 inch (20 mm) between stories(movement is not cumulative, but relativeonly between each floor level). This issignificant movement, although underworst case conditions. Placement ofmovement joints horizontally at each floorlevel, and vertically at strategic locations

such as along column or window edgesevery 1216 feet (45 meters) maximum ismandatory to isolate wall components andeliminate restraint of drift. The use of alow modulus or flexible adhesive is alsocritical in accommodating structural driftmovement (see Section 7 - AdhesiveCriteria).

In severe seismic or wind zones, theeffects of structural drift on direct adheredcladding can be further minimizedby isolating the underlying substrate with acleavage membrane and applying aleveling mortar over galvanized steelreinforcing wire fabric attached withflexible connections to the underlying

support wall or structure. The cleavagemembrane prevents partial bond andallows the cement leveling mortar substrateto float over the underlying back-up walland provide isolation from transmission ofstructural movement by flexible structuralconnections to the wire reinforcing.

Thermal Movement

All building materials expand andcontract when exposed to changes intemperature. There are two factors toconsider in analyzing thermal movement:

1) the rates of expansion of differentmaterials (also known as the linearcoefficient of thermal expansion)

2) the anticipated temperature rangeexposure

SECTION 4 Architectural & Structural ConsiderationsDirect Adhered Ceramic Tile, Stone &Thin Brick FacadesTechnical Manual 1998 LATICRETE International, Inc. 71

Figure 4.1-1 Types of structural movement


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The primary goal in analyzing thermalmovement is to determine both thecumulative and individual differentialmovement that occurs within and betweencomponents of the facade wall assembly.

For example, a porcelain tile has anaverage coefficient of linear expansion of

between 4 - 8 x 10-6mm/C/mm of length.Concrete has an expansion rate of 5 x 10-6

in/in/F (9-10 x 10-6mm/C/mm). Thesurface temperature of a dark tile mayreach as high as 140F (60C) in hot sun,and the lowest ambient temperature in amoderately cold climate may be 14F(-10C), resulting in a temperature range of158 F (70C) for the tile. The temperature

range of the concrete structure, notexposed directly to the sun and insulatedfrom temperature extremes by the tile, andleveling/adhesive mortars as well as lengthof time exposure, may only be 30C. For a50 meter wide building, the differentialmovement is as follows:Concrete .000010 x 50m x 1000mm x30C = 15mmTile .000006 x 50m x 1000mm x 70C =

21mmBecause the tile thermal expansion is

greater, this figure is used. The general rulefor determining the width of a movement

joint is 23 times the anticipatedmovement, or 3 x 21mm (.82 in) = 63mm(2.5 in). Minimum recommended width ofany individual joint is 10mm (3/8 in),therefore, a minimum of 6 vertical joints

(inclusive of corners) across a 50m (154 ft)wide facade, each 10mm (3/8 in) in widthis required just to control thermalmovement under the most extreme

conditions. Similarly, there is anapproximate potential differentialmovement of 6mm (1/4 in) over 50 mbetween the veneer and underlyingconcrete structure that must beaccommodated by the flexibility of theadhesive and leveling mortars.

Thermal induced structural deflectionor bending of the buildings structuralframe is another often overlooked cause ofstress on a direct adhered facade. Thisphenomena can occur when there is asignificant temperature differential betweenthe exterior and interior of the structuralframe, causing the frame to bend and exertforce on the exterior wall assembly. For

example, a 100F (38C) temperaturedifferential between the interior andexterior structural steel or concretemembers in an extremely hot climate withan air-conditioned interior can result in achange of length of 7/8 inch (20mm) over a100 foot (30m) distance. An engineeringanalysis to determine movement jointrequirements is mandatory, because, unlikea mechanically anchored wall finish with

flexible connections, the frame transmitsmovement directly to the fixed, directadhered cladding. This problem is moreacute in steel framed buildings.

Moisture Shrinkage/Expansion

Underlying structures or infill wallsconstructed of concrete or concrete

masonry will undergo permanent shrinkagefrom cement hydration and loss of waterafter initial installation. The amount ofshrinkage is dependent on several

Figure 4.1-2 Linear thermal movement of different porcelain ceramic tile sizes at normal maximumtemperature range for temperate climate


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variables; water/cement ratio of concrete,relative humidity/rainfall, thickness ofconcrete, and percentage of steelreinforcement. While an average of 50% ofultimate shrinkage occurs within the first36 months (depending on weatherconditions), the remainder can occur over

a period of 2 or more years. In a wet,humid environment, the period of highinitial shrinkage is difficult to predict. Ifpossible, it is recommended to sequence ordelay the direct application of claddingand leveling mortars until after the majorityof shrinkage of a concrete structure hasoccurred, which under ideal conditionsmay be about 6 months. If scheduling and

sequencing does not permit a 6 monthwait, it is recommended to wait aminimum of 45 to 90 days after theplacement of structural concrete,depending on humidity and drying/curingconditions, before installation of claddingor cement leveling mortars. In somecountries, such as Germany, there arebuilding regulations which require aminimum 6 month waiting period.

The reason for waiting period is that theamount and rate of shrinkage of theconcrete is greatest during the first 6 monthperiod, and there is no sense exposing theadhesive interface to differential movementstress if it can be avoided, as the claddingwill not shrink, and leveling mortars willhave a significantly lower amount and rateof shrinkage. Also, the concrete will reach

its ultimate compressive and tensilestrength within 28 days, and be much moreresistant to cracking after that period

As an example, reinforced concretewalls will ultimately shrink between.00025 to .001 times the length(.025.10%), depending on a number ofvariables such as concrete water/cementratio or the amount of steel reinforcing. Aconcrete framed building which is 120

ft/40 (meters) high can shrink up to 3/4"(18mm) vertically. Cladding will not shrink,and in some cases will undergo moistureexpansion (see Section 6 - Thin Brick). As aresult, there must be provision in themovement joints to absorb at least 3/4"(18mm) of contraction (joint width must beapproximately 23 times the anticipatedmovement, or 2 1/4" (54mm) total.

Assuming 10 stories at 12ft (4m) heighteach, shrinkage could add approximately1/4" (5.5mm) in width to the horizontalmovement joint at each floor level,depending on how much of the ultimateshrinkage has occurred at the time ofinstallation of the cladding.

Conversely, ceramic tile and thin brickcladding, as well as underlying clay brickmasonry back-up walls, can undergo longterm, permanent expansion from moistureabsorption. Dimensional changes inceramic tile can be virtually eliminatedby use of an impervious or semi-vitreoustile. However, thin or thick clay brickmasonry must be detailed with proper

movement joints to accommodatemoisture expansion. (See Section 6.4 -Thin Brick)

Structural Deformation

As a building is constructed, the weightof materials increase, and permanentmovement, known as elastic deformation,occurs in heavily stressed components of

the structure. For example, the spandrelbeam or lintel over the windows is allowedto move or deflect up to 1/500 of the span.Therefore a beam spanning 15 ft (5m)between columns is allowed to move 3/8in (10mm) vertically from initial positionunder full load. The spandrel beam istypically the optimum location for ahorizontal movement joint at each floor

level of a building. The joint shouldcontinue from the surface of the claddingand through the adhesive and levelingmortars. Similarly, it is also critical to leavea space between the bottom of thespandrel beam and the top of the backupmasonry wall to allow for this movement.The backup wall is not designed as a loadbearing wall, and may crack or bulge whendirectly exposed to loads from the floor

above. This space between each floor istypically filled with a compressible filler toallow for movement, flashed and sealed toprevent water and air penetration. Thebackup wall should be braced laterally tothe columns with masonry anchors andreinforcing.

Deformation movement in concretestructures, also known as creep, occurs

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more slowly and can increase initialdeflections by 23 times. Allowance forthis type of long term movement must beconsidered in the design of movement

joints. Creep is typically of greater concernin taller, reinforced concrete framebuildings, especially those that do notincorporate compressive reinforcing steelin the structural design.

Example:

A typical 10 story building is 130 feet (40meters) tall. Creep, or long termdeformation may be as high as .065% ofthe height. Creep would be calculated asfollows:40m x 1000mm x .00065 = (1 inch) 26mmpotential reduction in the height of the

concrete structure.

Differential Settlement

Buildings structures are typically designedto allow for a certain tolerance of movement in the foundation known asdifferential settlement. In most buildings,the effect of normal differential settlementmovement on the exterior wall assembly is

considered insignificant, becausesignificant dead loading and allowablesettlement has occurred long beforeapplication of the cladding. Differentialsettlement of a buildings foundation thatoccurs beyond acceptable tolerances isconsidered a structural defect, withsignificant consequences to a directadhered ceramic tile facade.

4.2 ARCHITECTURAL

CONSIDERATIONS

This section examines the architecturalpractices that contribute to the successfulperformance of a direct adhered facade.Exterior walls are complex assembliescontaining many materials and systemsthat must interface, and the performance of

the interface between components is asimportant as the individual componentsperformance.

Windows, Glazing, and WindowMaintenance Systems

In addition to satisfying obvious needsto provide interior daylight and exteriorviews, windows function in many of thesame ways as the other components of anexterior wall assembly. Windows controlheat flow and air infiltration, provideresistance to water and air pressures, soundattenuation, as well as an aestheticallypleasing facade.

While the functional and aestheticcriteria for selection and design ofwindows is beyond the scope of thismanual, it is important to consider the

windows interface with the direct adheredexternal cladding system.

Window Interface Requirements

Configuration and location of windows Mechanical connection of the window

frame (wall assembly or structure) Compatibility of materials

Figure 4.1-3 Control of concrete thermal movement by type of aggregate


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Water and air infiltration resistance Flashing a

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