Numerous failures of building seals and sealants have logical and, in most cases, simple explanations as to why the seal or sealant failed to function as intended. This paper focuses on a failure mechanism that is not as apparent or simple to explain; failure caused by improper mixing of two part sealant or the reversion of cured sealant. On two separate buildings with the same sealant, the authors encountered a varied mode of failure. This paper documents the investigation of one of these projects and discuses the failure phenomena in relation to the orientation of the sealant joints and the analysis of physical properties of seals exposed to varied conditions of ultraviolet radiation and elevated temperatures. It is concluded that reversion in certain types of polyurethane sealants compounded with benzoate based plasticizer is more likely when exposed to conditions of high levels of ultraviolet radiation and elevated temperatures.