A Plaster Manifesto
Michael Gardner / October 2020
Spend time with a financial planner and you likely will experience a retirement planning discussion centered on the “three-legged stool,” a metaphoric device used to describe the relationship between three typical retirement income sources: Social Security, savings and a pension or 401(k) plan. Underfund, or eliminate, one of the three legs and the two-legged stool that remains will be a bit wobbly. Retirement won’t be as much fun under that scenario.
An analogous comparison can be made regarding the participation of the three primary entities—enforcement, manufacturing and contracting or installation—involved in the model code and standard revision process. Lose or negate the input of one of the three “legs” and the resulting document may not be acceptably complete.
Unfortunately, a committee that oversees the content of an international portland cement plaster installation standard seems to be moving toward a two-leg model, largely because it is ignoring input from the contracting participants on a specific issue. Consequently, the working committee has fractured slightly, making progress on meaningful updates of the standard difficult.
The stalemate involves an impasse over language in Section 22.214.171.124. of ASTM C1063, Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster, which requires lath used as a base for an application of exterior portland cement plaster to “… not be continuous through control joints, but shall be stopped and tied at each side.” The contentious issue is whether the lath really needs to be stopped, or cut, at the control joint as prescribed in the noted clause.
The Contrators’ Position
Large segments of the contracting industry believe that lath can run continuous behind a control joint without adversely impacting the finished plaster; therefore, the lath does not need to be stopped in every circumstance. They also believe there is no difference in performance between a continuous lath application and a cut lath application, and they consider plaster cracking to be a composite outcome of numerous contributing factors, many of which are fully disassociated from the lath-cutting requirement. Citing a history of successful installations and regional practices, they think the standard should equally permit the use of either installation method and should declare no preference for one over the other.
Those in opposition feel that the lath must be stopped in every situation. They allude to the historic reference to the C1063 standard in contemporary building codes, a relationship between standard and code that makes the issue non-debatable. In this opinion, if the code references the standard and the standard requires the lath to be stopped, then the lath must be stopped in every instance at a control joint.
The debate has been ongoing on for a few years, hampered primarily by a lack of verifiable evidence to support the performance of either approach.
History Doesn’t Help
Most of the historic testing that has been conducted on the subject is largely visual, not data-driven, and, while the results are interesting, the individual tests suffer from shortcomings such as a lack of data, an inability to ground the testing via any type of consensus test method, questionable sample construction or a lack of independent verification. The history of the issue in model building codes also provides no clarity. Until the early 2000s, three regional building codes were used for code enforcement in the United States: the BOCA National Building Code in the northeast and upper Midwest, the Southern Standard Building Code in the Southeast and the ICBO Uniform Building Code west of the Mississippi River. In 2000, the regional codes were assimilated into a single document and re-branded and re-issued as the International Building Code.
The regional building codes largely ignored the issue of cut lath at control joints. The UBC, first published in 1927, never contained cut lath language. It also never referenced a standard, like C1063, that contained lath application language. The BOCA and SBCCI codes, each of which was first published in the mid-20th century, effectively did not address the issue until references to ASTM standards began to appear in each document in the late 1980s. It was not until a reference to the C1063 standard was inserted in the 2000 IBC that the requirement began to become universally codified.
The fairly solid “bright line” in the 1990s that marks when model codes transitioned from having no cut lath requirements to mandating cut lath is interesting because it should provide a theoretic point in time where a before-and-after comparison about the impact of the cut lath requirement on exterior plaster quality can be made. However, there is no existing evidence that the transition in code requirements improved the performance of exterior plaster. There is also no historic evidence that code-compliant structures constructed to a predecessor regional code where the lath was run continuous at control joints performed any different than code-compliant structures constructed to a code, either regional or the IBC, that required cut lath at control joints. There is also little to indicate that the historic cut lath requirement has any basis in testing. Cut lath advocates occasionally point to language published, possibly as early as the 1960s, in an ANSI document that preceded C1063: ANSI A42.3, Lathing and Furring for Portland Cement and Portland-Cement Plastering, Exterior (Stucco) and Interior. However, there’s no evidence that the language was inserted into the ANSI standard on the basis of any testing. And there is nothing to suggest that any testing occurred when the C1063 language was first created or when the reference to the C1063 standard was first placed into a model code.
It all begs for answers to two questions:
First, and most important, how do you rely on language that appears to have no real foundation in testing or performance? And second, in the contemporary marketplace, contractors not only have to know how to install the materials that have been used for decades, they also must be adept at incorporating newer, non-conventional materials. So how does that work with universal language that was written decades ago and now may be imposed on a material that has evolved over time or wasn’t available when the language was conceived?
It’s a bit ironic: Standards language that is intended to guide and protect a contractor actually could create an unseen liability for that contractor. And that has happened because contractors are getting hung out to dry by the requirement when it has been inappropriately used against them. It is not a pleasant situation when members of an important industry committee are operating at odds. However, it is not an insurmountable quandary, and I believe a path to resolution exists. It is not an easy path, but it will work: All parties need to come together and cooperatively test.
I suggest the following:
First, the interested parties on both sides of the issue should form a consortium to directly investigate and study the issue. This could occur within the framework of the ASTM C11 committee or through an alternate entity.
Second, the consortium should fund the creation of a standardized test plan to adequately address the issue.
Finally, assuming that a test plan palatable to all perspectives can be constructed, the consortium should fund relevant testing based on the plan. The results of the testing should be used to refine the language in the C1063 standard.
The results of the testing should be used to draft language for incorporation into relevant model building codes. This is not a situation where an incremental improvement in plaster quality effected by one method over the other should be the basis of determination. If the two methods achieve a reasonably similar performance, then each should be permitted. It is entirely possible that the continuous method might be a better performer. No need to throw away the cut lath method if it performs acceptably and works for some contractors. Contractors understand that, like it or not, they must build to code. But if the language referenced in a code creates a requirement that may serve no real defined purpose, why use the language? Why not look at modifying language to make construction more efficient and cost effective and create more, rather than fewer, installation options?
Nothing herein should be interpreted as disparaging of the ASTM standards process, the specific committee mentioned or the model code revision process; however, technical issues need justification and in the instance of the discontinuous lath debate, little or no justification for the requirement exists. That needs to be addressed as the exterior plaster industry can ill afford the ongoing debate to continue indefinitely.
Michael Gardner is the president of M Gardner Services LLC, a consulting firm that assists wall and ceiling industry clients with industry standards, building codes, material and system testing, and competitive product analysis. He is the former CEO of the Gypsum Association, was the executive vice president of compliance programs for the International Code Council and currently serves as a special technical advisor to the Wall & Ceiling Conference. He can be contacted at firstname.lastname@example.org.