IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 Bowlsb y | 91 Stuccometrics: Stucco Jointing – The Why, When, Where, and How Jeffrey A. Bowlsby, CCS, CCCA Simpson Gumpertz & Heger, Inc. 100 Pine Street, Suite 1600, San Francisco, CA 94111 415-495-3700 • Email: jabowlsby@sgh.com Jeff Bowlsby is an architect and stucco consultant with 35 years of construction industry experience. He leads the ASTM C1063 Installation of Lathing and Furring for Portland Cement-Based Plaster task group and founded and leads the ASTM C11 Stucco Work Group that develops all ASTM stucco-related industry standards. He has completed performance testing of stucco assemblies and components, published several stucco-related technical articles in national industry professional journals, is the author of the stucco information resource StuccoMetrics.com, and is a frequent industry presenter on stucco wall claddings. Bowlsby is skilled in building science issues and the integration of all building enclosure systems and components. 92 | Bowlsb y IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 ABSTRACT SPEAKER Exterior stucco cladding can be categorized into one of two configuration types—either directly applied to cementitious and masonry substrates (barrier walls), or applied over lathing that is mechanically fastened over a water-resistive barrier to steel- or wood-framed substrates (drainage walls). Both configurations often employ a range of stucco cladding jointing types serving different functional and aesthetic purposes. The objective facts of why and when stucco jointing is needed or not needed, where joints are needed, and how joints are designed and constructed are explored, including significant new information that promotes knowledge and understanding to improve the performance and quality of stucco claddings, which are often misunderstood. This article is based on historical development, design, and installation requirements; building code and reference standard requirements; and the results of recent stucco jointing performance testing. Provided illustrations will depict stucco jointing construction detailing, lathing accessories, splicing, intersection and termination requirements, and plaster application methods used to configure stucco jointing. This presentation factually and objectively explains essential requirements and considerations for effective stucco jointing to assist stucco cladding designers and craftspeople. Jointing facilitates drainage, accommodating building substrate movement and cement plaster shrinkage movement, thus reducing cracking, while it terminates cement plaster panel areas and has decorative purposes. WHAT IS A STUCCO JOINT? In the earliest days of portland cementbased plaster claddings (stucco), stucco joints did not exist. Stucco was simply a plaster applied over solid masonry substrates where the stucco surface was continuous, uninterrupted, and expressed the building as a solid visual mass—a barrier wall configuration. Stucco developed to be applied to metal lathing onto wood-framed substrates over what we now call the water-resistive barrier in a drainage wall configuration, where the first stucco joints were developed out of necessity. The first stucco joints were primitive configurations of stucco cladding edges, using wood profiles and metal flashings without lathing accessories, arranged to serve the primary functional needs of terminating the stucco and facilitating drainage. 1 In the following decades, a range of stucco lathing accessories were developed to further assist the installation of lathing and the application of stucco, and to support the functional needs of the stucco cladding system. The earliest stucco lathing accessory was patented in 1921 by J.J. Earley,2 followed by the casing bead in 1922 by L.E. Curtis3. These lathing accessories were intended to reduce stucco cracking at window corners by separating the stucco from the window, which created an edge for stucco becoming what I call the panel edge joint. In the 1950s, weep screeds, which are drainage joints, were invented.4 The 1960s brought us the control joint lathing accessory5 and expansion joint lathing accessory6 to “prevent cracking of walls and ceilings”—a lofty goal, to be certain— ultimately giving us the control joint and expansion joint. Then in the 1970s, extruded aluminum lathing accessories7 were introduced, which are used to create one type of decorative joint. Manufacturers continue to refine and improve lathing accessory designs, including the development of hybridized stucco joints such as combining crack reduction with water management functionality.8 A stucco joint is an intentional, visible joint at the stucco surface—most commonly in the form of a straight line (linear), but may also be curvilinear (Figure 1). Stucco joints are “interruptions in the plane of the plaster,” including expansion joints and control joints, as ASTM C9269 at 7.3.5 indirectly describes. A stucco joint can be either narrow and nearly imperceptible or wide for emphasized visual impact. Stucco joints are often the visual expression of an installed lathing accessory that provides specific functionality within a stucco cladding system. More specifically, stucco joints serve one or more functions as specified in ASTM C926, C106310, and C1861,11 such as: 1. Facilitating the installation of lathing and furring by: • Defining requirements of the lathing installation based on required stucco joint type (i.e., continuous or discontinuous lathing at stucco joints) 2. Facilitating the application of portland cement-based plaster by: • Providing an edge, end, or termination for a cement plaster panel area, by separating IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 Bowlsb y | 93 Figure 1 – Stucco cladding with stucco jointing on a contemporary multistory building designed in 2013 by Christiani Johnson Architects at 333 Harrison Street, San Francisco, CA. Stuccometrics: Stucco Jointing – The Why, When, Where, and How cement plaster from dissimilar materials, load-bearing members, and penetrating elements • Assisting in cement plaster thickness control • Avoiding cold joints by providing a place to temporarily end plastering for a workday, especially on larger buildings 3. Minimizing cracking by accommodating movements related to: • The building structural system substrate • Cement plaster shrinkage and curing • Thermal and moisture-related cement plaster expansion and contraction 4. Facilitating the water management functionality of the completed stucco cladding system by: • Limiting water infiltration that bypasses the stucco cladding • Defining requirements of the water-resistive barrier facilitating drainage • Facilitating water drainage from behind the stucco cladding by diverting water out 5. Providing decorative effects to the stucco cladding surface (utilizing a lathing accessory if needed) by: • Creating an artful expression on the stucco cladding surface • Creating shadow lines to emphasize building features or to make a design statement In the context of this article, those lathing accessories that are fully embedded into the stucco and are not visible at the surface are not stucco joints. Embedded external and internal corner reinforcements, such as strip lath and “butterfly” corner reinforcements, are not stucco joints. A Stucco Joint Is More Than Just a Stucco Lathing Accessory One of the significant challenges in the stucco industry revolves around terminology. The plethora of the same or similar terms used to describe different things causes differences of interpretations and misinterpretations. For example, for decades, the terms “control joint,” “expansion joint,” “control/expansion joint,” and other variations were used interchangeably, yet they describe different things. The central focus of this paper is the stucco joint, not the lathing accessory as a component of a stucco joint. While they are intrinsically related, the essential thing for the reader to recognize and understand is the importance of terminology that is widely misunderstood and misapplied in the industry. A stucco joint is not the same thing as a stucco lathing accessory. Peruse a lathing accessory catalog and you will see products for “expansion joints,” “control joints,” “reveal joints,” etc. Despite the use of the word “joint” in the name of the accessory, these are lathing accessories and not “joints.” To elaborate, an expansion joint lathing accessory is one component of an expansion joint as a functioning assembly. An expansion joint assembly consists of a specific configuration of several interrelated components and installation conditions that, when correctly configured, results in a functional expansion joint assembly that serves its intended functional purposes. The expansion joint assembly includes not only the expansion joint lathing accessory, but also other related components such as the structural substrate in two distinct, separately moving parts, a continuous water-resistive barrier, lathing (discontinuous), lath edge fasteners, and, of course, the cement-based plaster applied to each side of the expansion joint assembly. It is interesting to note that recent editions of ASTM C1063 make a subtle but clear distinction between the requirements for stucco joints and their related lathing accessories. For example, see ASTM C1063 at 7.4.9 for expansion joint and ASTM C1063 at 7.4.10 for control joint. Lathing Accessories A lathing accessory is at the heart of all stucco joints except one type of decorative joint. Lathing accessories have developed over the decades, continuing even today, as craftspeople and designers invent to realize unmet needs or determine a usefulness for new lathing accessories. Studying them carefully, one can see similarities among different lathing accessories, namely what ASTM C1861 describes 94 | BowlsbSBy IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 2 – Stucco cladding without stucco joints on the Santa Barbara County Courthouse, Santa Barbara CA, built in 1929 and designed by architect William Mooser III. as their “elements.” Individual lathing accessories are merely combinations of different elements, which, when combined together as a given lathing accessory, support the functional or decorative purpose of the stucco joint. ASTM C1861 identifies these elements as: • Attachment flange: solid or key • Ground • Capture flange • Movement gap • Flexible pleat • Drip flange • Drainage surface The drainage joint lathing accessory material, because it manages and is exposed to water, must be corrosion resistant as is suitable for the environmental conditions. Selecting the material of lathing accessories can be critically important to durability and is primarily based on the needs of the service environment of the stucco cladding. Lathing accessories are commonly manufactured in galvanized steel, solid zinc alloy, aluminum, and PVC/CPVC. A few manufacturers offer lathing accessories in stainless steel, copper, and galvalume materials. Each of these materials is generally acceptable in the comparatively dry and moderate climates throughout much of the United States. Corrosive environments in coastal climates or near industrial locations require more corrosion-resistant materials, such as solid zinc, stainless steel, or PVC/CPVC lathing accessories. Consideration must be given to the possibility of electrogalvanic action. Water is the electrolyte. For example, where stainless steel lath fasteners are required due to fire-retardant-treated wood framing, the lathing and lathing accessories must also be either stainless steel or of non-metallic materials. Further, be aware that solid zinc and PVC/CPVC lathing accessories have high coefficients of thermal expansion. Stucco cladding designers are required to indicate stucco jointing locations and provide detailing, including the lathing accessories, in the contract documents per ASTM C1063 at 7.4.1.1. This requirement is satisfied when the building exterior elevations depict or reasonably infer the locations and detailing of stucco jointing, not merely specifying generic location criteria and the various lathing accessories in specifications or drawing notes. In addition, designers are encouraged to provide detailing at stucco joint splices, intersections, and transitions. As a final comment about lathing accessories, consider their exposed finish when installed—this is often overlooked. Lathing accessory materials, where exposed at the surface, can be left exposed to weather to their natural patina. Extruded aluminum lathing accessories are often available anodized or receive a chemical treatment to prepare for painting. All metallic lathing accessories can be shop-painted or coated before installation. Some of the PVC/CPVC lathing accessories are available with integral color, no painting required. Stucco Cladding and Movements Because stucco cladding is a brittle material, movements in the building structural substrate to which it is bonded, or where mechanically attached via lathing and lath fasteners, may cause cracking. Cracking may also be caused by portland cement-based plaster shrinkage and thermal movements where not mitigated. Cracking is an aesthetic concern and may allow water infiltration. All minimum code requirements and reasonable methods to meet expectations for reducing cracking and minimizing water infiltration should be implemented. Movements in the building structural substrate result from many factors, including: • Building settlement • Structural member and cantilever deflections • Story drift in multistory buildings resulting from wind and seismic loads • Cyclical expansion and contraction of wood-based sheathings • Continuous insulation The dimensional magnitudes of these movements are determinable for each building structure based on an engineering analysis by a qualified structural engineer. The dimensional movements in the building structural substrate range from less than an inch to several inches, so obviously, cracks will occur if stucco spans over these substrate movement locations, if not mitigated with an appropriate stucco joint. The material properties of portland cement-based plaster include movements resulting from portland cement shrinkage during curing and from in-service thermal movements. The dimensional magnitudes of portland cement shrinkage movement during curing and from thermal movements are typically measured in mils or thousands of an inch. In summary, “cement plaster systems should be designed and constructed to accommodate from 100 to 200 mils of cement plaster shrinkage movement or more for every 10-ft. increment of cement plaster panel length.”12 Even with these seemingly small dimensional movements, stucco as a brittle material will crack if it does not accommodate these movements with an appropriate stucco joint. Restricting the function of movement joints by ornamental features such as foam plant-on trim that may impede the function of control joints or expansion joints may result in cracking. The designer needs to detail how ornamental features interact with movement joints per ASTM C926 at A2.6.4. Stucco Joints on Solid-Base Substrates IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 BowlsbSBy | 95 Lathing accessories have developed over the decades, continuing even today, as craftspeople and designers invent to realize unmet needs or determine a usefulness for new lathing accessories. Stucco can be an effective and durable cladding where it is fully and continuously bonded to solid-base substrates such as concrete, concrete masonry, and brick masonry. Solid-base substrates are commonly used in certain building types: parking garages, certain storage facilities requiring high strength or durability, and most buildings in locations with high wind or seismic loads. Solid-base wall assemblies do not generally require lathing or a water-resistive barrier (WRB) or stucco jointing to receive stucco because these wall assemblies are considered barrier walls from a water management perspective, and substrate movements are often of relatively minor dimension (Figure 3). Water is managed by deflection at the wall surface and by the absorption and release of water temporarily stored within the solid mass of the wall. Solid-base substrate walls typically only require limited if any, stucco jointing, as will be further elaborated on. Stucco Joints on Framed Substrates Framed, or framed and sheathed substrates of wood or cold-formed steel materials (which are the predominant substrate for stucco cladding throughout much of the country) represent the majority of small- to medium-scale buildings in the United States. Framed, or framed and sheathed substrates require a concealed WRB and water management materials, including drainage flashings, drainage joints, and movement joints. This paper focuses on stucco jointing as related to stucco cladding on framed or framed and sheathed substrates as a drainage wall assembly. The subject of stucco jointing in stucco cladding on framed or framed and sheathed substrates as face barrier assemblies, as a water management concept, is beyond the scope of this paper. Weather-Exposed Surfaces (WES) WHERE are drainage joints needed for exterior stucco cladding? The International Building Code (IBC), at Section 202,13 helps us to define that requirement by classifying certain exterior building surfaces as weather-exposed surfaces (WESs), a definition which has been in the codes virtually unchanged since the 1960s. The WES definition provides specific dimensional criteria to classify an exterior building surface as a WES where exposed to wind-driven rain. If an exterior building surface is a WES, then it requires stucco drainage joints for water management purposes. Caveats Emptor Regarding Stucco Jointing Aesthetic considerations: Designers with stucco cladding design responsibility need to recognize the essential requirements for compliance with minimum building codes regarding stucco jointing. Design to provide stucco joints for their functional characteristics and locate them where necessary, as a minimum. Some designers claim exemption or special dispensation for not providing stucco joints on the basis of a building’s architectural style or occupancy. Stucco cladding—whether on a house or hospital, on a building of contemporary or historical-revival architecture—requires stucco jointing as a matter of function and building code compliance, which are the minimum requirements of the stucco industry. Water management: Stucco joints may allow water leakage if of a type or installation configuration that allows water infiltration to bypass around the joint, such as at panel edge joints and where stucco joint splices, intersections, or transitions are not sealed watertight per ASTM C926 at A2.1.3. Defined drainage space: Traditionally, for framed or framed and sheathed substrates, stucco has been applied over a lath and a two-layer WRB. The self-furring mechanism for lathing furs the lath and has nothing to do with enhancing the drainage function. In recent years, a defined drainage space creating a capillary break above the WRB is becoming more commonplace within stucco cladding assemblies for enhanced drainage functionality and building science purposes, often using a three-dimensional drainage mat or vertical strapping over the WRB. The dimension of this defined drainage space can vary from 1/8 in. (3 mm) to ¾ in. (19 mm) and has implications to the physical configurations of stucco jointing. Where a defined drainage space is used in the stucco cladding assembly, the ground dimension of the lathing accessory must be of a dimension capable of accommodating that defined drainage space, which does not reduce the minimum required stucco cladding thickness. WHY, WHEN, WHERE, HOW Let us now explore the various individual stucco joints. Lathing and cement plastering are constructed on a building sequentially and in coordination with other work in progress on the jobsite. With construction order as the frame of reference, the first stucco-related component on the wall is the foundation weep screed, a component of a drainage joint. DRAINAGE JOINTS The drainage joint, although not explicitly named in ASTM standards, is a stucco joint characteristic that facilitates a drainage function by directing water from behind the stucco cladding to the exterior of the stucco cladding (Figure 4). WHY is the drainage joint needed? Drainage joints are useful to facilitate the 96 | BowlsbSBy IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 3 – Drainage joint construction detail. drainage of water that infiltrates behind the stucco cladding, out of the stucco cladding system. Additionally, drainage joints typically provide grounds for controlling cement plaster thickness. WHY is the drainage joint important? The drainage function of drainage joint assemblies can be the primary function of the stucco joint or ancillary to it. Examples of this often include expansion joints or control joints where the drainage function is part of, but ancillary to, the primary function of the joint. WHEN is the stucco drainage joint needed? Drainage joints are needed to facilitate drainage for drainage wall constructions. Any time an assembly has a concealed WRB, drainage joints are needed. Drainage joints are not needed for barrier wall construction or for soffit conditions where the soffit assembly is not a WES. WHERE are drainage joints needed? The IBC requires a drainage joint at the lowest point of a drainage wall construction, in the form of a foundation weep screed. It requires this to recognize that where water does infiltrate into, through, and behind the stucco cladding, it must be given the opportunity get out, assisted by gravity. For small-scale buildings of one- or two-story heights, a foundation weep screed has generally been the minimum codified requirement. Many entities in the stucco industry recognize that taller buildings with stucco cladding drainage walls are constructed today that are multiple stories in height or are in climates zones with large amounts of annual rainfall. Additionally, drainage joints are needed in buildings with stucco cladding drainage walls that require that drainage occur at other locations away from the foundation, such as above windows, doors, and louver openings; where stucco is above elevated balconies or terraces or roofs; and at weather-exposed soffit corners. For taller buildings, drainage joints are useful to facilitate drainage at approximately story-height intervals. These additional conditions can facilitate drainage with drainage joints as determined and designated by the building designer, using designated drainage screeds as described in ASTM C1861. Designated drainage screeds can be located at windows, door and louver head conditions, along WES soffit corners, and at story-height intervals to facilitate drainage. HOW is the drainage joint designed and constructed? Several considerations for drainage joints should be considered. Stucco-clad drainage walls on framed or framed and sheathed substrates require a WRB system to manage water. Certain climates with greater annual rainfall may additionally require a designated drainage space, which is typically created by a three-dimensional drainage mat or furring, located over the WRB. An important industry trend is to include drainage mats in stucco-clad drainage wall assemblies—even in moderate rainfall climates. ASTM C1063 and C1861 require that the drainage joint lathing accessory include a solid attachment flange, and that the WRB (and by association, an optional drainage mat) be lapped over the solid attachment flange to facilitate drainage. Because drainage joints are exposed to and manage water, every element of the drainage joint assembly must facilitate the drainage function, including the finish coat. Where polymer-based stucco finish coats are applied, they can be overlooked as potentially impeding drainage. Drainage screed performance testing14 has confirmed that polymer-based finish coats, where bridging the drainage gap of drainage joints, can impede drainage. Therefore, when applying polymer-based finish coats over drainage screeds, be certain to clean off the coating while it is still wet to preserve the drainage function of drainage joints. MOVEMENT JOINTS Panel Edge Joints The panel edge joint—although not explicitly named in ASTM standards—describes the edge condition of a cement plaster panel area, separates the stucco cladding from adjacent dissimilar materials, accommodates cement plaster shrinkage and thermal movements, and seals against water infiltration at the stucco edge (Figure 4). WHY are panel edge joints needed? Stucco cladding is applied to buildings and the stucco cladding must terminate somewhere, resulting in panel edge joint conditions. The panel edge joint (that is the term I use, although it is not found in any current resource) is constructed from casIIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 BowlsbSBy | 97 Figure 4 – Panel edge joint. ing bead lathing accessories to provide the ground for cement plaster thickness control and define the edge of a cement plaster panel area. Casing beads were the first lathing accessories intentionally developed for stucco claddings. Panel edge joints are categorized as stucco movement joints because of the movement inherent with portland cement plaster shrinkage and thermal movements at the extent of the plaster. ASTM C1063 at 7.10.4.1 recognizes the movement function of panel edge joints where it categorizes wall or partition height door frames as control joints. WHEN is the panel edge joint needed? Panel edge joints are useful for stucco claddings applied to both solid base substrates and framed or framed and sheathed substrates to terminate cement plaster panels. Stucco cladding applied to either substrate type terminates at wall openings for windows, doors, and louvers at a minimum. Panel edge joints are required and useful to separate cement plaster from dissimilar materials per ASTM C1063 at 7.4.6. Dissimilar materials requiring separation from stucco cladding include window, door, and louver assemblies and penetrating elements such as ducting and conduits. Fun fact: Why is the common casing bead lathing accessory called “Milcor” or the “No. 66”? Because in the Milcor Co. lathing and accessories catalog from a century ago, it was accessory No. 66. There were many other profiles with other numbers. WHERE is the panel edge joint needed? Panel edge joints are located at stucco cladding panel edges, which occur at all cement plastered surfaces, whether they be vertical walls, horizontal ceilings/soffits, or non-planar, curvilinear surfaces. HOW is the panel edge joint designed and constructed? Panel edge joints are constructed using the casing bead lathing accessory, which typically includes either a key attachment flange or a solid attachment flange and a capture flange. For maximum functionality—especially at suspended grillage—key attachment flange casing beads are wire-tied over the face of the lath to key with the lathing and cement plaster and move with them during cement plaster shrinkage and thermal movements. On the other hand, solid attachment flange casing beads are mechanically fastened to framing members where the lathing is lapped over the solid attachment flange, and the cement plaster during initial shrinkage and thermal movement slips in and out of the fixed casing bead within its capture flange. The continuity with adjacent wall components or termination of the WRB and a defined drainage space at either side of the panel edge joint must be designed by a competent designer. Where a defined drainage space is used in the stucco cladding assembly, the ground dimension of casing beads must be capable of accommodating the additional thickness for the defined drainage space, which does not reduce the minimum required stucco cladding thickness. Of critical importance and sometimes overlooked in certain geographic regions where stucco cladding is used at WES conditions, is that the gap created between a panel edge joint and the adjacent dissimilar material must be sealed watertight to prevent water infiltration per ASTM C926 at A2.1.3. Expansion Joints An expansion joint accommodates greater movement than cement plaster shrinkage and curing per ASTM C1063 at 3.2.3 and is intended to reduce cracking per ASTM C1861 at 4.6.1 (Figure 5). WHY is the expansion joint needed? Because the primary purpose of an expansion joint is to accommodate movement, it is categorized as a movement joint. Building structures are designed to move in response to the dead loads and live loads imposed on them, resulting in vertical and lateral displacements or movements. These movements can be oriented vertically towards the ground as for dead load deflections, horizontally from side to side as for seismic and wind load story drift joints, or both at the same time. The expansion joint separates structural building loads from transferring from one side of the expansion joint through to the other side of the expansion joint, minimizing stucco cracking. WHEN is the expansion joint needed? Expansion joints are especially useful for larger buildings where building structural designers need to accommodate building structural substrate movements to avoid damage to the stucco cladding. Differential structural substrate movements are managed by providing movement gaps in the stucco cladding between adjacent independent structural systems. Brittle stucco cladding, spanning continuously over these movement gaps without benefit of expansion joints, is susceptible to significant cracking due to the inherent inflexibility of the stucco cladding. WHERE is the expansion joint located? Framed or framed and sheathed building structural substrates may require expansion joints where the building structural system is large enough to require the accommodation of large dimension movements in the building structural system. Solid-base substrates expand and contract during curing, with thermal movements and with in-service structural loads. Solid-base substrates may include what the concrete masonry industry identifies as a “control joint.” Control joints in solid base substrates are typically a small continuous linear gap of typically 3/8-in. (10-mm) width in the concrete masonry. Cement plaster applied continuously over this gap, directly bonded to the solid base substrates on each side of this gap, will 98 | BowlsbSBy IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 5 – Horizontal expansion joint. likely crack. The solution is to provide an expansion joint aligned over the movement gap or “control joint” in the solid base substrate, often with a configuration of self-adhered flashing for water management purposes. Expansion joints are located wherever building structural substrate movements occur. These include stucco-clad exterior building surfaces without exception: walls, ceilings/soffits, and between adjacent construction, such as where roofs and large window systems meet stucco-clad walls. Expansion joints will typically be in alignment with and are expected to continue the performance of building expansion joints in other adjacent construction assemblies such as for roofing, foundations, and through other cladding materials. HOW is the expansion joint designed and constructed? A groove or cut in the stucco is not an expansion joint, per ASTM C926 at A2.3.1.3. Expansion joints are related to building structural movements, and specifically to the differential movement of separate adjacent components of a building’s structural system. In response to that, expansion joint lathing accessories are typically two separate pieces that nest or slide together to accommodate the building structural system movements. Because movement of the expansion joint is of the building structure (and not of the plaster or lath), each edge of the expansion joint lathing accessory is directly attached to the separate adjacent building structural systems at each side of the movement gap, to accommodate differential building structural system movement. Expansion joints are the termination point for the lathing and cement plaster matrix that defines a cement plaster panel area. The expansion joint lathing accessory provides the ground for cement plaster thickness control. However, the continuity or termination of the WRB and a defined drainage space at either side of the expansion joint must be designed by a competent designer. The essential characteristics of an expansion joint assembly include: • Framing and sheathing are discontinuous at the expansion joint because its primary function is to reduce cracking caused by building structural system substrate movement. • The WRB is continuous through the expansion joint, although overlapping its solid attachment flange to facilitate drainage. • The lathing is discontinuous at the expansion joint. • The expansion joint lathing accessory includes a movement gap to accommodate building structural system substrate movement, in tandem with the discontinuous lathing. • The expansion joint lathing accessory splices intersections and transitions are embedded in sealant to minimize water infiltration. Control Joints A control joint accommodates movement related to plaster shrinkage and curing per ASTM C1063 at 3.2.2 and is intended to reduce cracking per ASTM C1861 at 4.6.2 (Figure 6). WHY is the control joint needed? The control joint is widely misunderstood and is the most controversial stucco joint. Because the primary purpose of a control joint is to accommodate movement to reduce cracking, it is a movement joint. The effective use of control joints can reduce cracking, which is what the buildings codes require, but it is a mistake to misconstrue this as to eliminate all cracking. The control joint lathing accessory provides the ground for cement plaster thickness control. A control joint typically does not support a drainage joint function, but variant product offerings of the control joint lathing accessory may provide for drainage joint functionality. WHEN is the control joint needed? Control joints are required for cement plaster applications over lathing, over framed or framed and sheathed substrates, per ASTM C1063. To serve their purpose of accommodating plaster shrinkage and curing movements, and to reduce cracking, control joints are required on all building types and occupancies, of every architectural design esthetic, without exception. Although there may be certain architectural styling esthetics where control joints are not preferred, that does not eliminate their codified requirement. Even if a building occupancy is of certain uses such as residential or because the building owner does not want control joints, that does not eliminate their codified requirement. Control joints are typically not required over direct-bonded cement-based plaster continuously adhered to solid base substrates per ASTM C926 at A2.3.1. Control joints constructed from one or a pair of casing beads installed back to back are codified at ASTM C1063 at 7.4.10.1 and are a type of panel edge joints. WHERE is the control joint needed? Control joints are located within stucco IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 BowlsbSBy | 99 Figure 6 – Control joint, vertical orientation. cladding to define discrete cement plaster panel areas at all cement plastered surfaces, whether they be vertical walls, horizontal ceilings/soffits, or non-planar, curvilinear surfaces. ASTM C1063 at 7.4.10 provides the minimum dimensional requirements for cement plaster panel areas, including 144-sq.-ft. wall areas maximum, 100-sq.-ft. ceiling/soffit areas maximum, 1:2.5 cement plaster panel area length-to-width ratios maximum, and 18 linear ft. maximum panel edge dimension. One requirement that is often overlooked is ASTM C1063 at 7.4.10.4, which requires a control joint at locations where the ceiling framing or furring changes direction. While some view these control joint location criteria as guidelines, they are, in fact, codified minimum requirements or, in other words, the maximum allowable cement plaster panel areas and dimensions. A common misunderstanding about control joints is that if these minimum requirements are satisfied, no cracking will occur. The correct use of control joints improves stucco cladding quality and reduces cracking, but some cracking may still occur. Improved crack reduction can be accomplished by reducing these maximum allowed panel area sizes. The author recommends the following for a more effective use of control joints with stucco cladding: • 100-sq.-ft. maximum cement plaster panel areas, because smaller panel areas are less vulnerable to shrinkage cracking. • 10-linear-ft. maximum cement plaster panel edges, because control joint lathing accessories must be spliced at 10-ft. intervals, and cracking typically occurs at splices. Eliminating splices away from intersections eliminates splice cracks and conforms to the recommendations for 100-sq.-ft. maximum panel areas and 1:1.5 maximum length-to-width ratio. • 1:1.5 cement plaster panel length-to-width ratios, because cement plaster shrinks towards its centroid (center of panel area), and long rectangular panel area proportions tend to crack into smaller panels of 1:1.5 proportions, especially at conditions such as the backs of parapets. • Align at least one control joint at reentrant wall opening corners (typically window and door corners) to avoid reentrant corner cracking, which is not a current ASTM C1063 requirement. Cracking at reentrant corners is the most prolific stucco crack, which can be reduced or eliminated by locating at least one control joint at the wall opening reentrant corner. Most buildings have window and door wall openings, aligning a control joint with each reentrant corner, easily achieving the recommendations for smaller panel areas, and length-to-width ratio previously noted. Finally—frequently overlooked but very important—the exposed ends and edges of plaster panels or exterior work are required to be sealed to prevent water infiltration per ASTM C926 at A2.1.3. The fundamental tenet of water management with any building cladding is to prevent water from entering behind the cladding that can then enter into the building. The correctly installed common stucco control joint lathing accessory with capture flanges does not typically allow water intrusion along its length. However, stucco control joints often do allow significant bulk water infiltration behind the cladding at unsealed splices, intersections, and transitions. Splices, intersections, and transition locations are the exposed ends and edges of plaster panels or exterior work that must be sealed to 100 | BowlsbSBy IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 7 – Horizontal to vertical control joint intersection of a control joint. prevent water infiltration. Figures 6 and 7 depict sealant located at control joint splices, intersections, and terminations. Note that no sealant is above the drainage screed to promote drainage from the upper vertical control joint, yet the top end of the lower vertical control joint below the drainage screed is sealed to prevent water infiltrations at this control joint intersection. HOW is the control joint designed and constructed? The essential requirement for a control joint is that lathing must be discontinuous at the control joint lathing accessory per ASTM C1063 at 7.3.1.5. This lathing discontinuity provides the location for plaster shrinkage and thermal movements to occur, reducing cracking, where continuous lathing significantly restricts movement and promotes cracking. A groove or cut in the stucco is not a control joint, per ASTM C926 at A2.3.1.3. Because movement of the control joint is of the plaster or lath (and not of the building structural substrate), each edge of the control joint lathing accessory is attached to the separate adjacent lath edges at each side of the control joint, to accommodate cement plaster shrinkage and thermal movements. One example of an effective horizontal-to-vertical control joint intersection is depicted in Figure 8, which also provides a drainage function. The essential characteristics of a control joint assembly include: • Framing and sheathing are continuous at the control joint because the control joint’s primary function is to reduce cement plaster-based shrinkage and thermal movements, not building structural system substrate movements. • The WRB is continuous through the control joint, although overlapping its solid attachment flange to facilitate drainage. • The lathing is discontinuous at the control joint to accommodate cement plaster-based shrinkage and thermal movements and to comply with ASTM C1063 at 7.3.1.5. • The control joint lathing accessory includes a pleat to accommodate shrinkage and thermal movements, in tandem with the discontinuous lathing. • The lower key attachment flange is wire-tied to the lathing edge, not mechanically fastened to framing, to accommodate cement plaster-based shrinkage and thermal movements. • The control joint lathing accessory splice intersections and transitions are embedded in sealant to minimize water infiltration. Control joints are a panel area edge for the lathing and cement plaster matrices that define a cement plaster panel area. The control joint lathing accessory provides the ground for cement plaster thickness control. However, the continuity or termination of the WRB and a defined drainage space at either side of the control joint must be designed by a competent designer. One effective method of minimizing the visual impact of control joints is to fill them with sealant over a backer rod, color matched to the adjacent finish coat (Figure 8). STATIC JOINTS Decorative Joints The decorative joint, although not explicitly named in ASTM standards, is useful for decorative purposes only and not for any other functional purpose, including crack reduction. Decorative joints are categorized as static stucco joints. WHY is the decorative joint needed? Decorative joints of one type or another have existed for portland cement-based plastering since its earliest use as an exterior building cladding. In fact, portland cement was devised and patented by Joseph Aspdin in 1824 as an “artificial stone,”16 so it is natural to extrapolate that vision which attempts to make portland cement-based plaster applications look like real stone or other materials requiring joints. WHEN is the decorative joint needed? Decorative joints are used for stucco claddings applied to both solid base substrates, framed, and framed and sheathed construction. Decorative joints are used for aesthetic effect and not needed for any functional purpose. WHERE is the decorative joint needed? Decorative joints—because they are decorative—typically only vary the decorative stucco finish coat thickness and can be applied to any portland cement-based plastered surface, walls, or ceiling/soffits. The decorative joint faux jointing pattern—because it has no functional purpose—may be located anywhere on the stucco cladding surface between movement joints as desired to achieve the intended aesthetic effect. It does not need to align with other stucco cladding movement joints or wall openings for windows or doors. HOW is the decorative joint designed and constructed? Decorative joints are of two types: those with a lathing accessory IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 BowlsbSBy | 101 Figure 8 – Control joints with sealant filled to minimize visual impact. and those without. As a static stucco joint, the decorative joint does not replace the functionality of or requirements for stucco joints which accommodate movements, facilitate drainage, or any other function. For the first type of decorative joints that include lathing accessories, there are significant considerations due to the inherent implications with this type of decorative joint (Figure 9): • The decorative joint lathing accessory provides a ground for cement plaster thickness control and serves decorative purposes only. • A control joint lathing accessory can be used to create a decorative joint, what ASTM E226617 and EMLA 92018 refer to as an “architectural joint.” Because there is nothing architectural about it, the term “decorative joint” is more descriptive. Decorative joints can appear deceptively similar to control joints because of the name and usage of the control joint lathing accessory. A significant difference between the decorative joint and the control joint is that lathing is continuous at the decorative joint, and lathing is discontinuous at the control joint. Continuous lathing at decorative joints effectively negates any accommodation for stucco cladding movements and does little, if anything, to reduce cracking. Decorative joints are intended to be applied within cement plaster panel areas between regular control joints per ASTM E2266 at X2.8.6. 102 | BowlsbSBy IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 10 – Decorative stucco jointing (sgraffito). Castello Sforzesco, Milan, Italy, 15th Century. Figure 9 – Decorative joint. Another type of decorative joint is the use of reveals or channel screed lathing accessories, which may result in a wider or deeper discontinuity of the cement plaster cladding surface and augmented linear aesthetics and shadow effects. Channel screeds have the unique characteristic among decorative joints in their section profile to allow for perforations which allow the screed to perform a ventilation function. Channel screeds with ventilation provisions are useful when they are installed in weather-protected soffits or ceilings where ventilation of the framing cavity behind the decorative joint is desirable. For example, the ventilation provided by a channel screed is appropriate below waterproofed terraces and similarly at roof eaves that ventilate attic or interstitial framing cavities. • Review the catalogs of lathing accessory manufacturers for additional accessories that can be incorporated into decorative joints. • A caveat with using decorative joints on WESs: Be cognizant of the increased potential for water infiltration. Where designed and installed as static joints, the cement plaster should remain in tight contact with the decorative joint lathing accessory, which minimizes water infiltration around it. It is essential to seal the splices, intersections, and transitions of decorative joint lathing accessories watertight during installation to minimize water infiltration. The second type of decorative joint—a groove or cut in plaster only—is not a control or expansion joint, per ASTM C926 at A2.3.1.3 (Figure 10). A decorative pattern is simply scored or troweled into the finish coat of the stucco cladding to visually emulate a faux stone masonry or tile pattern. A trade term for this is sgraffito. The stucco base coats remain full thickness. Another application technique for the decorative joint masks off portions of the base coat, then adds the textured finish coat, leaving a faux jointing pattern when the masking is removed. TOUGH STUCCO JOINTING QUESTIONS, DEFENSIBLE RESPONSES 1. Are Window Frames With Formed Stucco Receivers Acceptable as Panel Edge Joints? Unfortunately, no. An installed window surrounded by stucco cladding is a dissimilar material from the stucco, which requires separation from the stucco with a panel edge joint and may allow water infiltration behind the stucco cladding where sealant is not provided. ASTM C1063, C926, and C1861 do not recognize a window frame as a lathing accessory to create a panel edge joint, which requires a casing bead and sealant. The typical gap that occurs at window and door frames as the stucco cures results from cement plaster shrinkage and thermal movements between the stucco and the dissimilar materials at window and door frames. This unsealed gap is a known and common water path that may allow water infiltration. Retroactive attempts to create an effective and durable sealant condition at this narrow gap to prevent water entry are not possible because the gap is too narrow. To avoid potential water infiltration at this condition, separation is required between the stucco and dissimilar materials per ASTM C1063 at 7.4.6, which specifically requires the use of a casing bead for this purpose. The stucco cladding system includes the casing bead lathing accessory (the casing bead is not a dissimilar material from the stucco cladding system); and a window or door frame is a dissimilar material. Reliance on stucco receivers integral to window and door frames is bad news for stucco cladding and should be avoided. Casing beads as separately installed lathing accessories are the only lathing accessory specified in C1063 and C1861 to separate stucco cladding from dissimilar materials and create panel edge joints. Further, panel edge joints are required to be sealed to prevent water entry, per ASTM C926 at A2.1.3. The design of this sealant joint between the casing bead and window or door frame is beyond the scope of this paper. The purpose of these codified minimum requirements for a casing bead and sealant at stucco panel edges at windows and doors is to benefit the water management performance of the stucco cladding assembly by keeping bulk water out from behind the stucco cladding. They are basic requirements of the stucco cladding system, regardless of other considerations such as for local annual rainfall amounts, window water-resistivity performance rating, window location related to grade, window dimension or type, mulled or unmulled frames, integral or field-applied attachment fins, or local traditions. Stucco claddings in wetter climates generally conform to these requirements because the builders and designers know better from experience. Reliance on integral window and door frame stucco receivers in drier climates is more common, to the great detriment of stucco when water infiltration occurs, which is avoidable and preventable with a perimeter casing bead and sealant panel edge joint. IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 BowlsbSBy | 103 The typical gap that occurs at window and door frames as the stucco cures results from cement plaster shrinkage and thermal movements between the stucco and the dissimilar materials at window and door frames. This unsealed gap is a known and common water path that may allow water infiltration. 2. Does an ASTM E2266 or EMLA 920 “Architectural Joint” Reduce Stucco Cracking as Effectively as an ASTM C1063 Control Joint? Unfortunately, no. Small-scale comparative control joint and decorative joint performance testing (Figure 11) performed in a laboratory and published in 200919 illustrated the beneficial performance in terms of movement capabilities of control joints. The full range of available control joint lathing accessories and installation configurations (including discontinuous lathing over decorative joint with continuous lathing) were tested. Recently, comparative large-scale control joint vs. decorative joint performance testing was performed on an exterior wall test apparatus in Galveston, TX. The purpose of the testing was to compare the crack reduction performance of control joints to decorative joints. According to the sponsors, “We wanted to document if cutting the lath promoted more movement during curing, thus reducing cracks,”20 and “to establish a benchmark for a final decision on best performance of a stucco assembly.”21 104 | BowlsbSBy IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 12 – Comparative control joint and decorative joint performance testing crack map, Galveston large-scale testing. Figure 11 – Control joint performance lab testing (small-scale testing). The specific decorative joint tested was a control joint lathing accessory installed over continuous lathing which is called an “architectural joint” in both ASTM E2266 and EMLA 920. Two reports and an article summarizing the Galveston testing were published.20,21,22 The conclusion was, “Leaving the lath behind the CJ appears to behave similar to cut lath (in that enough movement is allowed to relieve major internal stresses).”22 While the testing was imperfect and its reports and conclusions not peer reviewed, it had certain consistencies to provide meaningful information. I was peripherally involved as an observer during preparations for the testing and was invited to personally witness this testing apparatus on site to document my observations, and I reviewed the sponsors’ report data after publication. A summary of my primary observations of visibly obvious comparative metrics are depicted in Figure 12 and Table 1. My conclusions differ from the published reports and its conclusion, based on the information I documented and a comparison to the data the sponsors published. It is obvious from my documented observations and data I collected that the Galveston testing illustrated and quantified a visible and significantly improved crack reduction performance using control joints over decorative joints in portland cement-based plaster as evidenced by reduced cracking and, in some conditions, eliminated cracking. This evidence of reduced cracking is a basis for our codified minimum requirements for using control joints in minimum-quality stucco claddings in ASTM C1063 and C926—not decorative joints—and reduced cracking is ultimately what is or should be most important to building owners, design professionals, and craftspeople. 3. Does a Decorative Joint That Includes Various Non-Pleated Lathing Accessories Function the Same as a Control Joint? Unfortunately, no. ASTM C1861 at 4.9.2 describes the most common control joint lathing accessory as a single prefabricated accessory with key attachment flanges and a flexible pleat. Alternatively, a control joint can be assembled from a pair of casing beads installed back to back with key attachment flanges and a flexible element functionally similar to the pleat, between them, per ASTM C1063 at 7.4.10.1. Avoid using and beware of decorative joints that use one-piece channel screeds and other decorative joint lathing accessories without a pleat or flexible element as control joints to accommodate movements. Certain decorative joint lathing accessories are installed with discontinuous lathing, so they may appear at first glance to meet the current definition of a control joint. However, these decorative joint lathing accessories do not have a flexible pleat or similar flexible element required by ASTM C1861 3.2.6 and 4.6.2 to accommodate movement. Decorative joint lathing accessories may include narrow capture flanges or point screeds at the stucco-to-screed interface similar to window and door frames. When cement plaster is applied and shrinks away from this type of fixed, inflexible lathing accessory, a gap may develop that cannot be effectively sealed and that is known to allow water infiltration that may bypass around the decorative joint lathing accessory (Figure 13). Even where the decorative joint lathing accessory includes a narrow capture IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 BowlsbSBy | 105 Table 1 – Quantified results summary of comparative control joint vs. decorative joint performance testing, Galveston. Figure 13 – Decorative joint used as control joint with increased water leakage potential. flange to cover the gap, significant water infiltration bypassing the decorative joint lathing accessory may occur (Figure 14). On the other hand, where designed and installed as static joints within panels surrounded by movement joints, the cement plaster should remain in tight proximate contact with the decorative joint lathing accessory, which minimizes water infiltration around the decorative joint lathing accessory. It is essential to seal the splices, intersections, and transitions of decorative joint stucco joint lathing accessories watertight during installation to minimize water infiltration. 4. What Are the Risks Related to Shimming Stucco Jointing Lathing Accessories? Shimming lathing accessories may contribute to cracking from abrupt or extreme cement plaster thickness variations; they should not be necessary, and they are not recognized in ASTM C1063, C926, or C1861. These standards require the substrate to be planar within ¼ in. (3 mm) in 10 ft. (1 m), which corresponds to the requirement for uniform nominal plaster thickness. If necessary, small-dimension, gradual plaster thickness variations up to ¼ in. can be accommodated by distorting the key attachment flanges of lathing accessories to adjust grounds as long as the minimum nominal cement plaster thickness is maintained. REFERENCES All figures and photographs are by Simpson Gumpertz & Heger, Inc. 1. Portland Cement Stucco, Typical Construction Details. Publication P4. p.15, Portland Cement Association, 1920. 2. J.J. Earley. Patent 1355756, Flexible Joint for Stuccoed Buildings. 1920. 3. L.E. Curtis. Patent 1419232, Plaster Terminal. 1922. 4. “Method Developed to Alleviate Leakage Through Stucco Walls.” The California Plasterer. April 1953. Vol. XXVII, No. 9. California Lathing and Plastering Contractors Association. 5. Raymond Clark. Patent 3015194, Building Construction and Expansion Joint Therefor. 1962. 6. Ross Washam. Patent 3331176, Building Construction and Expansion Joint Therefor. 1967. 7. R.W. Arnett. Patent 3606714, Molding Strip for Use as Quirk or Reveal. 1971. 8. Donald A. Pilz. Patent US2008/0016808 A1, Building Construction Product Directed to Minimizing Water Accumulation at Floor Joints. 2008. 9. ASTM C926, Standard Specification for Application of Portland Cement-Based Plaster. ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959. United States. ASTM standards are available from the ASTM website for a nominal charge. Membership is available to interested parties for a nominal fee, which includes a volume of the Annual Book of Standards (C11 is in Volume 04.01) either printed or online at no additional cost. 10. ASTM C1063, Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster. ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959. United States. 11. ASTM C1861, Standard Specification for Lathing and Furring Accessories, and Fasteners, for Interior and Exterior Portland Cement-Based Plaster. ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959. United States. 12. Jeff Bowlsby, CCS, CCCS. “Cement Plaster Metrics: Quantifying Stucco Shrinkage and Other Movements; Crack Acceptability Criteria for Evaluating Stucco.” Proceedings of the RCI Symposium on Building Envelope Technology. November 2010. 13. 2018 International Building Code, International Code Council Inc. 5203 Leesburg Pike, Suite 1600, Falls Church, Virginia 22041-3401. 14. Jeffrey Bowlsby and Christine Diosdado. “StuccoMetrics: Performance Testing and Evaluation of Drainage Screed Flashings and Drainage Subassemblies Used in Stucco Drainage Wall Systems.” STP 1588, 2015. ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959. 15. Joseph Aspdin. British Patent No. 5022, Artificial Stone. 1824. 16. ASTM E2266-11, Standard Guide for Design and Construction of Low-Rise Frame Building Wall Systems to Resist Water Intrusion. ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959. 106 | BowlsbSBy IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 14 – Water testing decorative joints used as control joints; water infiltration occurred. 17. Guide Specifications for Metal Lathing and Furring, Fifth Edition. NAAMM EMLA 920-09, Expanded Metal Lath Association Division of the National Association of Architectural Metal Manufacturers (EMLA) 2009. 18. Bowlsby, Jeff. “Scratching the Surface with Stucco Control Joints,” The Construction Specifier. April 2009. 19. “Stucco Control Joint Research Project,” Walls & Ceilings Magazine. June 2018. BNP Media, 2401 W. Big Beaver Rd., Suite 700, Troy, MI 48084-3333. 20. “Stucco Control Joint Controversy.” Houston Lath and Plaster. May 7, 2018, 1904 Hialeah Dr., Seabrook, TX 77586. 21. Cement Plaster Control Joint Movement Study. 2017, Final Report Rev 2, 8.29.2018, Z6 Commissioning LLC, 2308 Avenue K, Galveston, TX 77550. IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 BowlsbSBy | 107
