Stucco Myths: Myth #2 – Control joints are required every 13.5 m2 (144 sf)
In our work as forensic architects and engineers, we are regularly involved in litigation over stucco failures, including hotels and high-rise condo complexes. (For this article, ‘stucco’ refers to traditional portland cement plaster direct-applied to a masonry substrate, rather than using lath.)
Myths abound around stucco cracking. In truth, it is not abnormal to have some cracking with stucco, much of which can be relatively harmless. The key is paying attention to the types of cracks, and minimizing any significant issues that might lead to actual failure, including debonding, water intrusion, and mold problems.
Myth #2: Control joints are required every 13.5 m2 (144 sf).
Replacement stucco on lath on same building shown above. Applied with knowledge previous stucco had cracked, it cracked as well.
While this measurement (and other spacing restrictions from ASTM C1063, Standard Specification for Installation of Lathing and Furring to Receive Interior and Exterior Portland Cement-based Plaster) are a requirement for stucco on lath, control joints (CJs) are not generally needed in direct-applied except for where the substrate changes. For example, if changing from CMU to concrete, a CJ should be added. If its presence causes aesthetic concerns, striplath can be considered as an alternate, but may cause cracking if poorly installed. (Different from CJs, stucco expansion joints are required where expansion joints occur in the building envelope substrate or movement is expected.)