One-Coat Stucco: Why?
One-coat stucco, once resisted by plasterers, has evolved into a practical, code-compliant, and energy-efficient alternative to traditional three-coat systems.
Mark Fowler
UP FRONT
It is common knowledge that construction professionals are often resistant to change. Yet refusing to adapt can be a worse alternative. Most plasterers dislike one-coat stucco. There, I said it. But why?
Years ago, I met with the president of a leading one-coat stucco manufacturer. As he began to pitch the benefits, I interrupted him. I explained that I had already heard the arguments when I was a plastering contractor, but felt the industry was missing the bigger picture by not listening to field plasterers.
Most plasterers preferred three-coat systems, and they had valid reasons. Working over a substrate that absorbed moisture, such as CMU or a scratch coat, allowed them to rod, cut angles, and shave the wall with the brown coat. These steps were tactile, skill-driven, and made plasterers feel like true craftsmen. With one-coat stucco, much of that “plasterer’s touch” was lost.
One-coat stucco emerged during the 1970s energy crisis. As energy codes increased insulation requirements, builders sought ways to maintain 2x4 framing while meeting higher R-values. Stucco manufacturers responded with a one-coat system applied over rigid foam. Plasterers initially resisted but developers liked the sales pitch: less masking, one less cement coat, shorter scaffold rental times. In practice, cost savings were minimal once insulation and proprietary cement costs were added. Still, over time, one-coat stucco became more popular and today, I often recommend it.
Why One-Coat Stucco?
The plaster industry is highly litigious, with codes and standards used in defect claims. Establishing fault can hinge on mix ratios, sand type, and other variables. Pre-blended mixes and manufacturer-backed systems provide protection for contractors, since liability can be shared with the manufacturer. One-coat stucco offers an even stronger defense, as evaluation reports and ASTM allowances give contractors added support against frivolous claims.
Energy codes are another driver. One-coat stucco was designed to work with rigid foam and easily meets continuous insulation requirements. While a three-coat plaster over foam is possible, verifying compliance with ASTM and building codes can be more difficult without manufacturer testing. With one-coat systems, code compliance is well-documented. Many manufacturers also allow their one-coat products to be applied at three coat thickness, offering the best of both worlds.
Enhanced drainage requirements further support the use of one-coat stucco. Tested assemblies using grooved foam and a single water-resistive barrier have achieved more than 90 percent drainage, meeting ASTM requirements across all U.S. climate zones. Other insulation products, such as mineral wool, are also being tested for compliance.
The Bottom Line
Plasterers and designers should reconsider one-coat stucco—not as a shortcut but as a code-compliant, durable and efficient solution. For residential projects, it provides affordable insulation and energy performance. For commercial work or applications requiring a thicker cement plaster, manufacturer approval allows installation at 7/8 inch thickness.
One-coat stucco may not replace tradition for everyone but it could be the answer to many of today’s plastering challenges.
Opening Background Image Credit: uschools / iStock / Getty Images Plus via Getty Images.
Mark Fowler joined Walls & Ceilings as editorial director in 2006. Fowler grew up in the construction business and has held a number of positions in different companies and associations. He spent 11 years with the Northwest Wall and Ceiling Bureau before moving to his position with Soltner Group Architects in Seattle. Fowler is currently the executive director of the Stucco Manufacturers Association. He can be reached at Mark@markfowler.org.
