The new portland cement-based plaster (stucco) industry standard is ASTM C1861–Lathing and Furring Accessories, and Fasteners for Interior and Exterior Portland Cement-Based Plaster1. C1861 is a product standard, as distinct from stucco material and installation standards long recognized in the stucco industry. It brings the benefits of standardized products to the stucco industry, explaining the purpose, functions and minimum requirements for individual accessories and fasteners to benefit stucco as a premium wall cladding. Architects, contractors and manufacturers are already specifying compliance with C1861 requirements.
What Is ASTM C1861?
C1861 is a product standard, based on the previous requirements found in stucco standards ASTM C9262, C10633 and C17874, where stucco application, lathing and furring installation requirements are specified. Improved information is added to reflect current industry practices and available products and materials.
The concepts for stucco lathing and accessories were just beginning to be understood as early as 1920 when the first stucco standard ACI No. 25 was published. ACI No. 25 described no stucco lathing accessories but had similar elements and detailing configurations performing basic functions such as for plaster thickness control, termination, and facilitating drainage from behind stucco.
Since then, numerous lathing accessories, furring accessories and fasteners have been under continual development to facilitate the functionality, serviceability and quality of stucco cladding systems.
C1861 summarizes its purpose:
C1861 @ 4.1.3 “Lathing and furring accessories shall facilitate lathing and furring installation, cement plaster application, and functionality of the completed stucco cladding assembly. Lathing and furring accessories shall be configured to serve one or more functions such as to assist in cement plaster thickness control, to reinforce cement plaster corners, to facilitate drainage, to reduce cracking by accommodating movement, 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.”
C1861 further includes improved terminology, materials and illustrations:
- 11 new terms to define and explain the functions of the discrete elements that combine to make lathing accessories – capture flange, cement plaster panel area, drainage surface, drip flange, fastener, flexible pleat, movement gap, ground/screed, and solid/key attachment flanges.
C1861 @ 3.2.6 “flexible pleat, n—the flexible element of a control joint lathing accessory that accommodates movement of the cement plaster cladding assembly caused by shrinkage and thermal variations.”
- Improved materials list—Includes steel (G60), stainless steel, zinc alloy, anodized aluminum, PVC and CPVC.
C1861 @ 3.3: 30 new “Illustrations are intended to generically depict examples of common lathing and furring accessory shapes and fasteners, by depicting their functional elements in relationship to each other, without literally depicting specific manufactured products. Variations of lathing and furring accessory shapes and fasteners illustrated shall be acceptable when the function and performance is equivalent to or exceeds the illustrated accessory or fastener.” (See Figure 1.)
- Fastener specifications—Table 3 lists acceptable fasteners and requirements in one convenient Table – including as nails, screws, staples, power-actuated fasteners, eye screws, adhesives and tie wire. Fastener requirements for placement into fire retardant-treated and preservative-treated wood are referenced to code requirements. (See Figure 2.)
Traditionally, stucco has generally been viewed as wall cladding only, not a part of a protective water management system to protect buildings, but with the exception of lathing accessories with drainage functions such as the weep screed, lathing accessories are not considered to be flashings per se.
In the last decade or so, certain lathing accessories have begun to include drainage as a functionality and with the recent development of requirements for a drainage space behind stucco in some climates, heightened emphasis will be placed on drainage as an essential function for stucco claddings in general and for lathing accessories specifically.
C1861 presents the current state of minimum requirements for lathing accessories, describing their functional elements and purposes. Combining these elements in different ways leads to innovative new accessories such as the Finish Rite accessories from Stockton Products, Water Management accessories from CEMCO and the backer bead and E-flange products from Clark Dietrich Building Systems and others. Combining various basic C1861 elements into new innovative lathing accessories will lead to a promising future for stucco as a premium wall cladding.
Because C1861 concerns the functional requirements of lathing accessories, decorative accessories such as soffit vents, channel screeds and banding beads are not specified.
Process to Codify C1861
C1861 has been a second-tier reference standard in C1063 since the 2021 IBC and 2021 IRC and since that time its requirements have been enforceable by local Authorities Having Jurisdiction (AHJ) who have adopted those code editions. C1861 is under review by the International Code Council (ICC) this year for codification as a primary reference standard beginning with the 2027 I-code editions.
ICC’s review and codification process for the new C1861 reference standard includes testimony before the ICC code development committees, reviews, and ultimately voting by ICC governmental members before receiving codification.
How Does C1861 Serve the Industry?
Codifying minimum requirements for lathing accessories, furring accessories and fastener products leads to enhancing the functionality, serviceability and quality of stucco cladding systems, to benefit stucco as a premium wall cladding.
However, the work on C1861 is not yet complete. More can be done to improve C1861 by interested people participating in the ASTM C1861 task group to contribute your knowledge. Topics that require further development include requirements for…
- Lathing accessories and furring accessories for curved substrates and archways
- Stainless steel and other corrosion-resistant fasteners
- Sealant to seal the splices, intersections and transitions of lathing accessories to prevent the entry of water per C926 A2.1.3
- Lathing accessories configured for use as drainage flashings
- Generic pre-engineered furring accessory systems
- And more….
Contact Don Pilz, AWCI director of technical services and current C1861 task group chair at [email protected] for more information on participation.
(1)ASTM Standards are available from ASTM International at www.astm.org.
(2)ASTM C926 Standard Specification for Application of Portland Cement-Based Plaster
(3)ASTM C1063 Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster
(4)ASTM C1787 Standard Specification for Installation of Non Metallic Plaster Bases (Lath) Used with Portland Cement-Based Plaster in Vertical Wall Applications
Jeff Bowlsby, ASTM Fellow, is a licensed architect in California and Nevada and is a stucco consultant with Simpson, Gumpertz and Heger based in Northern California. He specializes in exterior wall and stucco assembly consultations to architects, contractors and manufacturers. His nationwide practice focuses on new building enclosure design, renovations and forensic evaluations. Jeff chaired or co-chaired several ASTM stucco committees over many years including ASTM C1063 and C1861 and is the author of Stuccometrics.com.
