Control Joints in Stucco

May 2015

Q: When installing control joints in a portland cement stucco system, is it necessary to cut the lath?

A: According to ASTM C1063, Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster, the lath must be cut:  “ Lath shall not be continuous through control joints but shall be stopped and tied at each side.”

However, this particular issue has been the subject of debate for many years and, at the time of this writing, is up for discussion again among the keepers of ASTM C1063—and for good reason. Before 2006, ASTM C1063 was a voluntary standard that design professionals and contractors could agree to follow for a stucco installation, but its practices were not mandated by any legal authority. If ASTM C1063 had been the agreed upon standard in a contract but was not adhered to during construction and the system failed, there was legal recourse available to the owner for not adhering to the terms of the contract. But in 2006, ASTM C1063, among other standards, was cited by reference in the International Codes, which in turn meant that once adopted by a jurisdiction, unless otherwise amended, it became the law. So, what was once offered as a “best practice,” which was one offering of many, became the lone practice to the exclusion of all others.

This turn of events has resulted in an increased sense of urgency to modify ASTM C1063 and its companion standard, ASTM C926, Standard Specification for Application of Portland Cement-Based Plaster, so that they leave room for other proven acceptable practices that do not currently appear in the documents. And as the members of the task groups that maintain the two standards are for the most part the same people, they have set up an informal group with the mission of ensuring that changes in one of the standards do not conflict with or leave omissions in the other standard. So, to prioritize the topics taken up in these standards, the stucco work group recently asked its members for position papers recommending changes and the rationale for the suggested changes.

One AWCI member, Past President Mike Boyd, who is also the co-chairman of the task group for ASTM C1063 and the facilitator for AWCI’s Stucco—Doing It Right® program, has submitted a position paper on the issue of control joint installation. AWCI supports his position, says AWCI Executive Vice President & CEO Steve Etkin. Mark Fowler, vice president of the Western Wall and Ceiling Contractors Association, has also submitted a letter that shares Boyd’s position.

In his paper, Boyd explains why the proposed change is necessary: “Up until 2006, reference documents prepared by industry associations/bureaus across the country carried the same weight as ASTM C1063. Many of these ‘bureau standards’ were developed for the sections of the country covered by the respective bureaus and were based upon many decades of successful installations on buildings and exterior wall configurations of all types. These documents were generally developed by industry professionals, including contractors and bureau representatives that had spent their life in the lath and plaster business. Very few, if any, outside engineers, consultants, attorneys, etc., were a part of developing these standards.”

Later in the same document: “The ASTM C1063 committee of today is for the most part driven by consultants, engineers and manufacturer representatives. Contractor participation is rare. Many of the people making the decisions have never been a contractor, never have installed metal lath and lathing accessories and do not have on the job, real world experiences to rely on. Many of the people that serve on the current ASTM C1063 committee because of the nature of their practice only see the failures or problem projects. This is just such a small sample of the work being performed across America but, in my opinion, skews their thinking and their ability to understand the need for alternative means-and methods.”

Fowler offers his perspective: “I also prefer the control joint over continuous lath. However, I would not force my personnel preference on anyone who prefers to have the lath discontinuous. I believe it is in the best interest of the "entire" lath and plaster community, to allow regional practice, preference and personal experience to play an equal role in that of laboratory testing. We do not build in the lab, we build real buildings, and real life experience should count.”

And the conclusion of Etkin’s letter stating AWCI’s support for Boyd is this: “AWCI agrees that ASTM C1063 should be modified so that it allows and presents alternate methods for such things as installing control joints without cutting the lath. This modification will allow design professionals and contractors to include methods they know to work and avoid being penalized for not complying with the letter of the law.”

So, if you’re a contractor who would like to ensure that the codes do not continue to limit your ability to use tried and true methods, you might consider joining ASTM and weighing in while this and other issues are being resolved.

Lee G. Jones is AWCI’s director of technical services.