Energy code requirements are pressing designers to install foam as a thermal break between framing and all exterior claddings. These requirements are primarily based on testing metal framing and claddings. The conductivity of metal is called short circuits and experts recommend continuous insulation on the outside of the framing. Exterior insulated finish systems are the obvious first choice. However, some designers are skeptical of EIFS and want cement stucco. But can it be done? Should it be done? Is it legal? All are good questions.
The practice of putting cement plaster or stucco over foam is not new. Cement plaster has been applied over foam for many years. This fact can be verified by the Portland Cement Association’s manual on cement stucco as they describe cement plaster adhering tenuously to foam substrates with historical use in large coolers and freezer rooms. Older plasterers noted that while the plaster functioned as intended, there was often the problem of excessive hairline cracking. Many regions of the United States and Canada have experimented with cement plaster over foam with mixed results. However, when certain principles and design guidelines are followed, they have proven to function well.