A Decade of Change: Recent Revisions to ASTM Stucco Standards Matthew J. Innocenzi, RBEC, PE Nick Innocenzi and Sons Consulting Engineers & Associates, LLC 20 Ashby St., Ste. 101, Warrenton, VA 20186 540-216-3224 • minnocenzi@niscea.com and Patricia M. Aguirre, REWC, CDT Bristow, VA 703-369-0996 • tricia@tros.org IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 Innoce nzi and Aguirre | 225 226 | Innoce nzi and Aguirre IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 ABSTRACT Although stucco has been in use for centuries, standards regarding its design and application were not developed until the early part of the twentieth century. Over time, these standards have been modified in response to changing needs, developments, and expectations within the industry. Revisions to stucco-related ASTM standards have accelerated over the past ten years in particular, changing the standards drastically. This paper will summarize the most significant of these changes and discuss the genesis and reasons for them. It will also examine areas of future progress on the standards anticipated over the coming decade. Matthew Innocenzi is principal of his firm. He has 20 years of experience as an engineering consultant, with a focus on litigation support and expert testimony for building enclosure systems, particularly light-gauge metal framing, portland cement stucco, brick veneer systems, steep-slope roofing materials, and waterproofing. Innocenzi is also an active member in ASTM C11 and D08 committees on Gypsum and Related Building Materials and Systems and Roofing and Waterproofing, serving as chairman and technical contact for ASTM C926, Standard Specification for Application of Portland Cement-Based Plaster and ASTM C1860, Standard Test Methods for Measurement of Tensile Strength or Bond Strength of Portland Cement-Based Plaster by Direct Tension task groups. Patricia Aguirre is a building enclosure consultant in northern Virginia. Her work focuses on forensic field and laboratory investigations; façade and building enclosure investigations; structural inspection, analysis, and design; architectural retrofit and repair; and development of design documents and repair recommendations. Aguirre is an active member of IIBEC, serving on the REWC Exam Committee and teaching several exterior wallrelated courses. She also serves on ASTM C11 Committee on Gypsum and Related Building Materials and Systems. SPEAKERS INTRODUCTION With the advent of the International Code Council (ICC) in 2000, standards governing the application of exterior portland cement plaster (stucco) and lath became codified. Both the International Building Code (IBC) and the International Residential Code (IRC) referenced stucco standards ASTM C926, Standard Specification for the Application of Portland Cement Based Plaster, and ASTM C1063, Standard Specification for the Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster. Seemingly overnight, these documents, whose content was often based on anecdotal performance, became the codeprescribed requirements for the installation of lath and stucco and evolved rapidly as litigation projects prompted explanation, interpretation, and revision of the language. In addition, advancements in building science and technology also prompted revision, such as nonmetallic lath, acrylic coatings, and foam ornamental features. This paper reviews some of the most significant changes over the past decade and provides an explanation for the reason(s) that initiated the change. In addition to the changes and revisions to the ASTM C926 and C1063 standards, a brief discussion of new stucco-related ASTM standards is provided. ASTM C926 Ornamental Features Stucco is a versatile building cladding material that can be formed to a myriad of different shapes. Window accents, floor line trim, parapet copings, rustications, and quoins are common and popular aesthetic features used by architects throughout a building’s exterior. In the 1990s and early 2000s, expanded polystyrene (EPS) foam was a popular choice as a backing material for ornamental features as it was lightweight and relatively insensitive to moisture. A common practice involved adhering the ornamental feature onto the surface of the stucco finish coat. Often, the foam bands would be adhered around window openings and conceal a portion of the control joints that aligned with the window jambs. In more daring applications, the foam trim was adhered along vast lengths of horizontal and vertical control joints (e.g., floor lines) in an effort to disguise the visually offending joint with a projecting accent. While the concept and approach seemed simple and harmless enough, the attachment of foam accessories to the stucco finish soon proved to be a problem. A separation (either a joint or an imminent crack) at the interface of the ornamental feature with the stucco surface would form. Water would soak into the foam core of the ornamental feature where it would be retained for long periods of time. In some cases, the additional weight of the water-logged foam core would exceed the shear capacity of the adhesive used to attach the trim to the face of the wall, resulting in failures and hazards from falling debris. In other cases, the absorbed water would build up hydrostatic head to the point that it would be forced through cracks and separations in the stucco. Because cracks and separations are often found around control joints, the alignment of these ornamental features over horizontal and vertical control joint accessories was particularly problematic from a water infiltration perspective. In 2015, design considerations relative to the design and installation of foam-based ornamental features were added to the Appendix of ASTM C926. In essence, the language required the foam feature be fastened to the stucco brown coat (as opposed to the finish coat) and covered in a continuous application of finish coat that extended onto the vertical portion of the wall itself. A design example is included in the Appendix that features an acrylic finish coat applied over impact-resistant mesh which, in turn, is applied over the foam core and extends onto the brown coat of the stucco (Figure 1). The methodology ultimately provides a rein- A Decade of Change: Recent Revisions to ASTM Stucco Standards IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 Innoce nzi and Aguirre | 227 Figure 1 – Sample detail for an ornamental feature. Reprinted, with permission, from ASTM C926-19a, Standard Specification for Application of Portland Cement- Based Plaster, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM International, www.astm.org. forced, continuous finish coat to mitigate the formation of cracks and separations at the interface of the foam band and the surface of the wall. Without the formation of a crack or separation, water is unable to saturate the core of the trim, allowing for a more durable detail. Nominal Thickness For years, the term “nominal thickness” as used in ASTM C926 has created confusion and debate. Both the IBC and the IRC add to this confusion, as they provide the same values for thickness as ASTM C926, with the exception that the codes prescribe them as minimum values. This conundrum triggered several construction defect claims for stucco that was allegedly applied too thin and did not meet code requirements. In 2013, text was added to Section 7.1 under the “Application” section of the main body of the standard to address nominal thickness as follows: The nominal values expressed in Table 4 represent neither a maximum nor a minimum value. They consider the inherent variation of thickness due to the nature of the application process, and the allowable variation of the substrate and the finished plane of the plaster. Additionally, a new Section X1.4.2.6 (later reorganized to X1.5.2.6) was added to the Appendix of ASTM C926. This section pertains to the application of stucco basecoats and describes the interaction between the plaster and lath/accessories during application. In this description, Item 4 offers a commentary on the term “nominal” as it relates to the thickness of the plaster. Per this explanation, “nominal” was specifically chosen as the thickness of the plaster is expected to vary due to the nature of its application. In the authors’ experience, treating the thickness values listed in ASTM C926 as nominal values is appropriate. For a successful stucco cladding project, the objective is to apply stucco such that it is thick enough to cover and protect metal lath from corrosion (especially in coastal environments where brackish air can result in rapid deterioration of the lath), but not so thick so as to compromise the bond or holding capability of the lath and associated fasteners. Thicknesses less than those tabulated in ASTM C926 may perform successfully in arid climates and/or where corrosion-resistant materials (e.g., stainless steel or nonmetallic) lath and accessories are used. In all cases, the evaluation of the stucco thickness should be left to the judgment of a design professional. With respect to an upper bound on thickness, it is possible that excessively thick stucco could exceed the bond strength of the stucco or the shear capacity of the lath and fastener assembly. The authors’ experience has shown that there is little, if any, correlation between thickness and tensile bond. However, additional research and study are required to determine the relationship, if any, between stucco thickness and shear bond (i.e., the tendency for excessively thick stucco to slide vertically off the wall). Generally speaking, experience has shown that stucco can be applied as thick as 1¼ in. (32 mm) without adverse effects. Maintaining a fairly uniform thickness throughout the stucco cladding is of greater importance than adhering to a strict maximum limit. Abrupt changes in plaster thickness can cause stress concentrations that lead to cracking and poor performance. Other Revisions Other revisions of note in ASTM C926 include: • Requirement that plaster be applied by hand trowel or by machine, effectively prohibiting application using slickers, screeds, or other suboptimal tools • Deletion of items that were redundant with ASTM C1063 • Migration of items within ASTM C926 dealing with lath and accessory installation to ASTM C1063 • Inclusion of nonmetallic lath as suitable plaster base ASTM C1063/ASTM C1861 Bifurcation of ASTM C1063 The greatest change to ASTM C1063 during the past decade has been the bifurcation of the standard. ASTM C1063 has, since its inception, been governed by the ASTM C11.03 subcommittee, which maintains and develops standards pertaining to the application of gypsum and related construction materials. Prior to ASTM C1063-18, the standard provided requirements both for fasteners and lathing accessory materials and for installation of lath and accessories in one document. Beginning in April 2018, these requirements were split into two documents. ASTM C1063-18 retained the lath and accessory installation requirements, while the material specifications were moved to a new subcommittee (ASTM C11.02, which maintains and develops standards related to the materials and testing procedures for gypsum and related construction materials). Within the new subcommittee, the materials specification became its own new standard, ASTM C1861, Standard Specification for Lathing and Furring Accessories, and Fasteners, for Interior and Exterior Portland Cement-Based Plaster. As an example of how the information is split between the two subcommittees and standards, ASTM C1861 now indicates which lath fasteners can be used and what their material properties must be, and ASTM C1063 specifies their spacing and embedment depth. The former addresses the materials while the latter describes the installation. The purpose of this split was to streamline the ASTM C1063 standard to make it easier to use. Before the new standard was developed, fastener and lathing accessory material requirements were scattered 228 | InnoceCEnzi and Aguirre IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Maintaining a fairly uniform thickness throughout the stucco cladding is of greater importance than adhering to a strict maximum limit. throughout the document, with some items being stipulated in the general, up-front sections and others located in more specific sections. In ASTM C1063-17b, nails, screws, and staples were described in Section 6.8 in terms of their general dimensions (e.g., diameter/crown size). However, their required lengths were provided in Sections 7.9.2 and 7.9.3. Powder-actuated fasteners (PAFs) were not described in the general fastener section (Section 6.8) at all; rather, their requirements were laid out in Section 7.9.5. All of these requirements have been centralized in ASTM C1861, where a new table, Table 3, summarizes the requirements for all of the permitted fasteners to simplify design and installation (reproduced in Table 1). An expanded version of the table originally in ASTM C1063 summarizing minimum required thicknesses for each type of accessory (e.g., weep screed) for each permitted material (i.e., galvanized steel, zinc alloy, etc.) is now located in ASTM C1861. Addition of Stainless Steel as an Acceptable Material for Lath, Fasteners, and Wire Ties As part of the development of ASTM C1861, new materials were added for lathing accessories and fasteners. In ASTM C1063-17b, lathing accessories were permitted to be fabricated from the following materials: • Galvanized steel (G60 coating) • Zinc alloy • Anodized aluminum alloy • Rigid PVC and CPVC Similarly, fasteners were to be fabricated from the following materials: • Nails were to be galvanized. • Screws were to have “corrosion-resistant treatment” through reference to other ASTM standards. • Wire was to be galvanized. • Materials for staples and PAFs were not specified. In brackish, humid environments such as coastal Florida, galvanized steel materials IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 InnoceCEnzi and Aguirre | 229 Table 1 – Lath and lathing accessory fastener requirements. Reprinted, with permission, from ASTM 1861-18, Standard Specification for Lathing and Furring Accessories, and Fasteners, for Interior and Exterior Portland Cement-Based Plaster, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM International, www.astm.org. tended to have shortened service lives as a result of corrosion in the salt-laden, moist air. PVC accessories can ripple or split after prolonged exposure to ultraviolet light due to their thermal properties. (Interestingly, PVC accessories have a coefficient of thermal expansion that is an order of magnitude greater than their metal counterparts). In response, manufacturers began producing stainless steel expanded metal lath and nonmetallic lath, as well as stainless steel accessories (nonmetallic lath is not included in ASTM C1063 or ASTM C1861, and will be discussed in greater detail later in this paper). Although stainless steel has not yet been included in the expanded metal lath materials standard (ASTM C847, Standard Specification for Metal Lath), its use has become more common in coastal locations. Due to their relative positions on the galvanic scale, it is unwise to pair stainless steel with galvanized steel, zinc, or aluminum, as contact with these dissimilar metals can result in accelerated corrosion from galvanic action (sometimes referred to as “galvanic corrosion”). A similar phenomenon occurs when galvanized fasteners are used in preservative-treated (PT) lumber. Since the early 2000s, PT lumber has been treated with copper-based preservatives; copper and the zinc plating used to “galvanize” fasteners are located far apart on the galvanic scale. In order to accommodate installation of stainless steel lath or fastening into PT lumber, accessories are now permitted to be fabricated from stainless steel in addition to the materials listed above. Fasteners (nails, screws, staples, and PAFs) are permitted to be galvanized, coated, or stainless steel. Wire ties are permitted to be either galvanized or stainless steel. ASTM C1063 has long exhorted consideration of climatic conditions in the selection of lathing and accessory materials, either in nonmandatory notes (ASTM C1063-16c and prior) or in mandatory language within the body of the standard (ASTM C1063-17 to present). Language has been added to both ASTM C1063 and ASTM C1861 to require consideration of material compatibility to address galvanic corrosion: • ASTM C1063-17, Section 6.1 (similar to reorganized Section 5.1 in more recent versions of the standard): “Metallic materials including lathing, lath accessories, and fasteners shall be selected for compatibility to minimize galvanic corrosion between adjacent metallic materials installed in the cement plaster cladding assembly.” • ASTM C1861, Section 5.1: “Lathing and furring accessory, and fastener materials shall be compatible with each other and with other materials in the cement plaster cladding assembly.” New Drainage Accessories Weep screeds at the base of walls have been explicitly required by the IBC since its inception, and by the IRC since 2003. In a similar fashion, the requirements for weep screeds at the base of walls have been included in the “Design Considerations” section of the ASTM C926 Annex and ASTM C1063 for several years. However, the codes have never required additional intermediate drainage provisions in the field of stucco cladding systems. Accordingly, many tall, stucco-clad buildings have been constructed with flashings at openings and a foundation weep screed, but no other means of diverting water on the drainage plane to the exterior. Given that such buildings can be tens of stories tall and—even in properly constructed stucco, the water-resistive barrier (WRB) is punctured hundreds or thousands of times 230 | InnoceCEnzi and Aguirre IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 Figure 2 – Example of a designated drainage screed. Reprinted, with permission, from ASTM 1861-18, Standard Specification for Lathing and Furring Accessories, and Fasteners, for Interior and Exterior Portland Cement-Based Plaster, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM International, www.astm.org. by lathing and accessory fasteners— significant water intrusion can and does occur. In 2016, Section A2.2.1 of ASTM C926 was revised to include a requirement for drainage accessories in conditions where drainage walls are located above barrier walls (i.e., where lathed construction is stacked above direct-applied plaster). While the standards still do not prescribe the frequency of flashing location on multistory buildings, a common practice is to prescribe and install drainage accessories at every other floor line to accommodate up to 20 ft. of wall height. Accessory manufacturers began fabricating accessories with drainage elements intended to provide drainage at intermediate locations to relieve the foundation weep screed. Examples of these new accessories have been included in Figure 1 of ASTM C1861, and they include horizontal expansion joints and control joints incorporating drainage surfaces as well as a newly defined accessory called a “designated drainage screed” (examples of which are excerpted in Figure 2 and Figure 3 herein). The purpose of the designated drainage screed is described further in Section 4.3.2 as follows: Lathing accessory located at designated exterior locations in addition to the bottom of exterior framed, or framed and sheathed walls, such as at floor lines of multi-story buildings, at soffit corners, above wall openings and projecting elements; used as a screed to assist in cement plaster thickness control; to facilitate drainage; to separate cement plaster from dissimilar materials, load bearing members and penetrating elements; and to provide an edge, end, or termination for a cement plaster panel area. OTHER REVISIONS Other notable revisions to ASTM C1063/ASTM C1861 include: • Installation requirements for furring for suspended ceilings was moved from the main body of ASTM C1063 to Annex A1. • Appendix X1 (nonmandatory) was added to ASTM C1063 to provide direction regarding maximum lath laps. • New terminology and figures were included in ASTM C1861 to better describe lathing accessory styles and requirements, • Nails and staples are now required to meet ASTM F1667. • Adhesives (not including expandable foam adhesives) are permitted for attaching accessories to solid plaster bases. NEW STANDARDS ASTM C1787/ASTM C1788 As discussed earlier, one way that manufacturers responded to the need for more corrosion-resistant materials in harsh environments was to develop nonmetallic lath. To ensure the nonmetallic lath that entered the market would perform appropriately within a stucco cladding system, ASTM developed two new standards: ASTM C1787, Standard Specification for Installation of Non Metallic Plaster Bases (Lath) Used with Portland Cement Based Plaster in Vertical Wall Applications, and ASTM C1788, Standard Specification for Non Metallic Plaster Bases (Lath) Used with Portland Cement Based Plaster in Vertical Wall Applications. ASTM C1788 is analogous to ASTM C1861 in that it is a material specification for nonmetallic lath, while ASTM C1787 is similar to ASTM C1063 because it is strictly an installation standard. Both nonmetallic lath standards were first promulgated in 2014. IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020 InnoceCEnzi and Aguirre | 231 Figure 3 – Example of an accessory incorporating a designated drainage screed with a horizontal control joint. Reprinted, with permission, from ASTM C1861-18, Standard Specification for Lathing and Furring Accessories, and Fasteners, for Interior and Exterior Portland Cement-Based Plaster, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM International, www.astm.org. ASTM standards are continually undergoing review and revision to adapt to changes in the industry, resolve conflicts in requirements, and respond to requests for interpretation of existing language. ASTM C1860 Direct-applied stucco refers to plaster that, as its name implies, is directly applied to solid substrates that are intended to receive plaster. Common substrates to which stucco is directly applied include concrete masonry units (CMUs), cast-in-place concrete, and stone masonry. For centuries prior to the advent of chemical admixtures and bonding agents, stucco bonded well because of the rough surface texture that provided a mechanical interlock between the stucco and the substrate. Additionally, the substrate’s ability to draw water from the plaster during application was beneficial to providing sufficient and intimate bond. In the early 2000s, construction defect claims were triggered from allegations that stucco was not sufficiently bonded to CMUs and/or concrete substrates. Many of these claims were based on sounding the samples for acoustical anomalies, a sound that represents a hollow and potentially delaminated condition. Until recently, there were no criteria for quantitatively testing the bond, nor was there a means to determine whether the values were acceptable. In 2017, a new ASTM test method (ASTM C1860, Standard Test Methods for Measurement of Tensile Strength or Bond Strength of Portland Cement-Based Plaster by Direct Tension) was published, providing a means to test stucco via mechanical tensile testing. This testing not only provides a consensus-based protocol and procedure for testing the stucco, but it also includes nonmandatory guidelines for interpretation of the results and analysis of the data for site-specific conditions in the Appendix. FUTURE ACTION ITEMS ASTM standards are continually undergoing review and revision to adapt to changes in the industry, resolve conflicts in requirements, and respond to requests for interpretation of existing language. Topics currently under discussion include: • Location of the datum for measuring stucco thickness • Reconciliation of stucco finish coat requirements • Curing requirements • Continuous insulation • Crack reduction methods • Drainage efficiency ASTM International promulgates stucco-related standards with consensus from manufacturers, contractors, industry associations, design professionals, and anyone with an interest in portland cement-based plaster. More information on the standards and their development can be obtained from ASTM International at www.astm.org. REFERENCES ASTM C926, Standard Specification for Application of Portland Cement-Based Plaster. ASTM International. West Conshohocken, PA. 2019. www.astm.org. ASTM C1063, Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster. ASTM International, West Conshohocken, PA. 2019. www.astm.org. ASTM C1787, Standard Specification for Installation of Non Metallic Plaster Bases (Lath) Used with Portland Cement Based Plaster in Vertical Wall Applications. ASTM International, West Conshohocken, PA. 2019. www.astm.org. ASTM C1788, Standard Specification for Non Metallic Plaster Bases (Lath) Used with Portland Cement Based Plaster in Vertical Wall Applications. ASTM International, West Conshohocken, PA. 2019. www.astm.org. ASTM C1860, Standard Test Methods for Measurement of Tensile Strength or Bond Strength of Portland Cement-Based Plaster by Direct Tension. ASTM International, West Conshohocken, PA. 2019. www.astm.org. ASTM C1861-18, Standard Specification for Lathing and Furring Accessories, and Fasteners, for Interior and Exterior Portland Cement-Based Plaster. ASTM International, West Conshohocken, PA. 2018. www.astm.org. 232 | InnoceCEnzi and Aguirre IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020
