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. It is not a good idea to pack out stucco so thick it may end up debonding and falling on those Bentleys (and their owners) below.
Myth #3: Direct-applied stucco is easily packed out to meet a finished plane.
Sometimes high-rises go slightly out of plumb as they are constructed. This creates a change in the substrate vertical plane that contractors often pack out with unreinforced extra lifts of stucco in an attempt to keep the finished stucco surface plumb. This added weight can create too much stress on the stucco bondline, causing the stucco to eventually fall off.
The difference in thickness with adjacent stucco also increases the likelihood of cracks developing. To solve out-of-plane conditions, a series of engineered reinforced mortar lifts may be needed. Where stucco has been erroneously packed out without reinforcing, a fix may include pinning.
Authors: Richard Scott, AIA, NCARB, LEED AP, is a senior forensic architect, Charles Allen, AIA, is a forensic architect, Steve Gleason, PE, is a senior forensic engineer.
Adapted from an originally published article in Construction Specifier. Source URL: >http://www.constructionspecifier.com/stucco-myths-and-facts/ May 4th, 2016.