Masonry Magazine February 2012 Page. 42
LATHS AND STONE
Unfortunately, contractors across North America may be installing sheets that fall short of current ASTM standards in terms of weight, length, width and/or metal galvanization. This sub-standard quality is being produced and marketed as "utility" or "nominal" lath, without intention to meet current ASTM C-847-10 standard. Examples of "utility" or "nominal" lath include G-40 galvanizing, (versus required G-60), lath sheet lengths of 96 inches (versus the minimum of 97 inches) and lath sheet weights that fall below the advertised 2.5 pounds to a 2.1 pounds per square yard. The production of utility lath offers manufacturers raw material savings that, in turn, is offered as a reduced price that attracts consumers. To further complicate the lath dealer's purchase process, some manufacturers offer a "code compliant lath," but only when specifically requested and sold at a premium price.
Yet, contractors who install stucco or stone systems according to ASTM standards depend on the dealer to provide lath products meeting industry standards. This product expectation typically is not questioned, but should be. There are various ways lath manufacturers can assure the lath dealer and installer of producing and supplying quality products. One method is requiring the lath manufacturer to submit to third-party testing reports, demonstrating compliance to ASTM C-847-10, defined under ICC's Acceptance Criteria 191. This third-party testing can be performed by an IES accredited laboratory, or another third-party testing laboratory. Typically, these tags are attached to the pallet during manufacturing.
One manufacturer has developed a packaging method to take the third-party identification all the way down to individual bundles that are supplied to the jobsite, each bundle has the lath weight. Whatever the method chosen, the intent is to provide full disclosure to the dealer and contractor purchasing lath sheets produced to proper dimensions and weights as defined in the ASTM C-847-10 standard.
The Expanded Metal Lath Association (EMLA) Division of NAAMM -National Association of Architectural Metal Manufacturers is a trade association formed back in the 1970s. EMLA's goal is to promote the use of expanded metal lath in building construction by providing technical data to support the architect or engineer's design needs to for lath and framing design.
In 2009, EMLA members performed an exhaustive edit to the original EML/SFA-920, first published in 1991. This renamed document "EMLA-920-09," sub-titled "Specifications for Lathing & Plastering of Steel Framing Systems," was updated with new terminology, installation details, etc. That revised document is available as a free download at www.naamm.org/technical. More recently, EMLA saw the need to publish quantitative values on transverse loading, using expanded metal lath on three-coat stucco. So, EMLA developed an RFQ for running transverse load testing on six framed wall scenarios, following the criteria outlined in ICC's-AC191 (Acceptance Criteria for Evaluating Expanded Metal Lath). EMLA hired an IES accredited lab in Los Angeles, and asked the Technical Services Information Bureau (TSIB, a division of the Western Wall and Ceiling Conference) to assist by having the local union build the four-X 4-foot test frames of the six separate wall systems. The AC 191 requires six tests of each wall system, requiring 36 panels to be tested. These systems include: Both 2.5 pound 3.4 self-furring, Expanded Metal Lath in a three?coat stucco over exterior gypsum sheathing attached to 3 5/8 inches X 33mil X 33ksi min. (20 ga) metal studs spaced at 16 inches on center with #8 modified truss screws.
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February 2012 www.masoncontractors.org