In January, Walls & Ceilingsheld the Webinar “Continuous Insulation: Plaster & The Energy Code.” During the Q&A following the presentation, many questions were asked.
With all the talk about continuous insulation, many designers desire cement stucco and wonder if stucco and CI are viable, has it been done, what are good practices, etc. This blog is designed to provide the answers to your questions. Here’s one to start us off:
Question # 1: Has cement stucco ever been done over rigid foam, I have always been told it is not a good idea?
Cement plaster (stucco) has been applied over rigid foam for many years, mostly in limited use areas, and yes it can be problematic for cracking. Generally, placing a hard, thin brittle shell over a softer substrate is not a good idea. However, the plaster industry never had polymer-enriched cements and the fiberglass mesh before recently. This lamina (mesh and skim coat) provides a strong, flexible and vapor-permeable layer that can almost guarantee no cracks. Even without the lamina, following some good practices can greatly minimize cracking. We (the WWCCA) have projects with cement stucco over rigid foam performing well. The plaster industry does have caveats and recommendations gained from our experiences.