Plastering is a time-honored and traditional industry. ASTM C1063 is the father for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster and has been the guide for the industry for decades. 

Plastering is a time-honored and traditional industry. ASTM C1063 is the father for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster and has been the guide for
the industry for decades. ASTM C1063 was derived from the American National Standard Institute A42.3. Much of the original language put into the ANSI standard is still in the latest edition of C1063 (2008). And as our building codes make a move from the more prescriptive standard to a more performance-based standard, isn’t it time for ASTM to do the same?

The fast approaching International Energy Conservation Code will radically change the way wall and ceiling contractors currently build the exterior envelope. The requirements of the IECC will encourage the use of continuous insulation on framing supports to reduce thermal bridging and increase energy efficiency for the exterior envelope by reducing the U factor. The IECC requirements apply to all cladding assemblies-a concept that is now being referred to as “cladding neutral.” For structures clad in exterior plaster, the IECC requirements will apply to lathing and furring for commercial and residential construction, which currently fall under the guidelines of ASTM C1063. ASTM C1063, as it is written today, will not provide the guidance to meet the requirements of the new code.

To further complicate the issue, the Steel Framing Alliance and New York State Energy Research and Development Authority published a report entitled “Siding Attachment to Cold-Formed Steel Walls Through Varying Layers of Foam Insulation.” The report notes the challenges for siding attachment with the increasingly higher levels of continuous insulation being specified. The report further notes that all cladding industries have been lacking in the type of fastener and siding installation that should be used when installing over thicker levels of rigid insulation.

The first task is to gather information, both empirical and consensus based, to help designers, contractors and building inspectors best utilize Portland cement plaster. The Western Conference has already started in that direction by gathering the technical experts in plastering from the western United States. 

Reference of Insulating Properties

The current ASTM C1063 makes no reference to insulating properties required in the IECC or allowance for rigid foam substrates. However, ASTM C-926, the companion standard to C1063 and the standard for applying Portland cement plaster, requires a metal base (lath) when cement plaster is to be applied over rigid foam substrates.

C1063 is comprised of prescriptive references that served the lathing and plastering industry well for decades as a guide specification. However, when referenced as “code” language, the standard makes no concessions for alternative methods-and there will be many new/alternative methods required to construct IECC compliant exterior walls and ceilings. While some contend that moving the standard away from its prescriptive roots and into a performance position is a “watering down” effect, I disagree. By making the C1063 Standard a performance-based standard and using the requirements as outlined in the Construction Specification Institute’s Manual of Practice, the furring and lathing installations are free to represent more “real world” applications. The “Alternate Materials, Designs, Tests and Methods of Construction” section of the International Code was established for this purpose. The International Code intends to allow design and construction innovation and refuses to squelch American ingenuity.

It is widely accepted that we cannot continue to construct inefficient buildings without regard to energy conservation. The national and local codes will soon reflect the need for those changes and force us to implement them. Without a performance standard in the national model code, our ability to meet these needs could be unnecessarily restricted.

While the Western Conference has a jump-start on the issue in the west, ASTM C11.03 Chairman Don Smith, Mike Boyd and myself are in the process of revamping C1063 to meet the needs for the nation. Mike Boyd is also the chairman of the AWCI Energy Task Force Group and we fully intend to make this ASTM process transparent and open to all. 

Base Line Construction Technique Development

The AWCI Energy Code Task Force is working to design base line construction techniques that will be tested for compliance and constructability once the final numbers have been published outlining the different zones and required U factors for each climate zone. States, such as California and New York, have already adopted their own energy code and contractors in those areas are trying to adapt on the fly. Other cladding industries, not wishing to lose market share, have been scrambling to ensure compliance with the new code.

The Western Conference of Wall and Ceiling Institutes recognized this fact and noted that the plaster industry has been doing this for years with one-coat stucco and EIFS. This fact, combined with the Western group’s past experience of cement plaster having been applied over rigid foam for decades, led the Western Conference to publish the brochure entitled, “The Energy Code and Plaster Assemblies,” ( This free online brochure is meant to give architects and contractors an idea of what has been done successfully and what limitations they need to know exist with applying cement plaster over rigid foam sheathing.

The Western Conference task group had no intent to thumb its nose at ASTM or other respected standards but action needed to be taken and we took the lead. Some people in the stucco industry would prefer things should just remain the same. If we do not change, we run the risk of extinction or worse yet, letting others determine our fate. We know cement plaster better than the outsiders looking at our industry and licking their chops: cement plaster is not just another cladding, it has unique characteristics and can be the best or worst cladding for a building, depending primarily on the qualifications, knowledge and skill of those installing it. We need to be proactive and lead our industry.

Western Conference has also recently developed a guide specification and series of generic details that will be unveiled by Frank Nunes and Bryan Stanley for the Webinar “Continuous Insulation: Plaster & The Energy Code,” on January 26 (see the news story on Page 9 for more details and to register). The Western Conference knows the future is coming and changes will take place. We have a longer range and more comprehensive plan for stucco to ensure the designers get what they need: A quality, affordable and functional cement plaster stucco that is energy code compliant. The details in this brochure and the ones forthcoming will be a lot easier to implement into the construction documents with a more progressive, forward-thinking and performance-based ASTM C1063.

Industries that make and install claddings other than plaster are faced with the same challenges and have undoubtedly taken similar actions to protect their market share. Fortunately, we have some help from the Foam Sheathing Coalition. The FSC has recently published a technical paper “Guide to Attaching Exterior Wall Coverings Through Foam Sheathing to Wood or Steel Wall Framing.” This technical report has explicit design data to assist designers and contractors in attaching various claddings over rigid foam sheathings. The cladding is defined by the weight of the cladding (i.e., 3 psf, 11 psf and 25 psf). The 11 psf weight cladding is not a coincidence, as the FSC has accurately concluded that 7/8-inch cement plaster weighs about 10.4 psf installed. This important research and test data must be taken into consideration at the ASTM level.

ASTM is a consensus standard with voices heard from manufacturers, contractors and designers. The intent is to have a truly wide range of experts collaborate on a standard and when agreement is reached, the document is perfect. OK, we know that is a fantasy, but in reality we should be able to come to a uniform agreement and have a standard we can all live and work with. The standard is not meant to be a tool for defect experts to use in litigation to nitpick good honest products and installation meeting the intent of the code. ASTM C1063 standard needs to reflect how we will build in the future-more energy efficient and sustainable construction. The initial writing of C1063 was prior to the invention of many of the newer products that can help the industry meet those goals. Let’s not become a dinosaur; the time for serious re-vamping is now.

We encourage everyone to participate in the re-write of a new ASTM C1063 Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-Based Plaster that will bring our industry into compliance with the new IECC. When all is said and done, we believe performance should have the last word.