Aguirre, Patricia1 and Innocenzi, Matthew2

1 Senior Engineer, Building Technology Consultants, Inc., 1845 East Rand Rd. Suite L-100, Arlington Heights, IL, United States, paguirre@btc.expert
2 Principal, Nick Innocenzi & Sons Consulting Engineers & Associates LLC, P.O. Box 1124, Warrenton, VA, United States, minnocenzi@niscea.com

ABSTRACT
In direct-applied stucco applications, the bond both between the stucco and the substrate, as well as that between individual stucco coats, is of paramount importance for reasons of both durability and life-safety. Prescriptive methods of achieving bond are provided in codemandated standards and are well documented within the industry. However, direct-applied stucco is a field-applied material that is highly sensitive to substrate preparation, workmanship, and environmental conditions. Because of the myriad factors that can influence bond, the expectation to achieve full bond over an entire building is likely unattainable. Small, localized areas of unbonded stucco typically would not be considered significant enough to justify repair or recladding, but where larger areas of unbonded stucco are found, the decision-making may not be so straightforward. Because the costs of either repairing or recladding a building can be significant, it is imperative that a way of determining whether an unbonded area of stucco is of sufficient size to necessitate such action. This paper presents a method for determining the maximum acceptable size of an unbonded area of stucco. The method involves calculation of an applied bending stress for the unbonded area under code-prescribed design loads using plate mechanics. An allowable bending stress is determined based on the stucco modulus of rupture and a site-specific safety factor.

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