Limit States and Service Life of Cement Renders on Façades

Abstract

The research presented in this paper is related to the durability of cement renders on façades, based on fieldwork data relative to the condition and extent of degradation of 100 façades of residential buildings in Portugal. Deterioration paths are obtained for staining, cracking, and detachment that show the loss of performance of the façade over time until a critical minimum acceptance level is reached, which is considered an estimated durability limit. These degradation patterns are analyzed individually to confirm whether any of three types of defects can effectively be considered limit states for the durability of cement renders on façades. The combined effect of all the defects that occur is also modeled as a single degradation path, and the expected service life is quantified. The results confirm that detachment constitutes a limit state of cement-rendered façades because it directly affects the physical durability of renders. Staining and cracking alone do not generally tend to signal the end of the physical durability threshold of renders, regardless of their impact on the performance and visual quality of the façade. However, when all degradation mechanisms are considered simultaneously, the estimated durability intervals correspond to a 50% additional decrease of the physical durability limit of renders. These results are in line with the general perception of damage to the façade, on which the decision to repair is based. The conclusions suggest that actual service life should be used (as reference service life), as opposed to durability data obtained through limit state conditions.