A Critical Review of Adhesion Strength Testing Standards for Mortar Coatings: Implications for Practice

The durability and safety of building facades, especially those continuously exposed to harsh weather conditions, are highly dependent on the adhesion of mortar coatings. The pull-off test is a commonly employed method to evaluate adhesion due to its simplicity and accessibility. However, discrepancies in the evaluation criteria across different standards can lead to variations in the results and their interpretation, impacting the assessment of coating quality. This study aims to compare the adhesion evaluation criteria outlined in three relevant standards. The analysis is based on facade inspection test results obtained from buildings in Brasília, Brazil. The research methodology includes processing test data in accordance with each standard, classifying outcomes as pass, fail, or discarded, and calculating the degree of convergence (DC) between these results. The comparative analysis reveals significant differences in the statistical approaches used to analyze adhesion performance. The Brazilian standard for tensile bond strength emphasizes frequency-based criteria, resulting in more conservative assessments and a higher likelihood of failure, even when values are near the threshold. In contrast, the Brazilian standard for potential tensile bond strength adopts a mean-based approach controlled by standard deviation, reducing variability but potentially discarding relevant data. The European standard for tensile bond strength, by comparison, offers a more lenient evaluation, focusing on the mean values, though it is susceptible to the influence of outliers. Moreover, a critical gap was identified across all standards regarding the consideration of rupture modes, which could undermine the precision of adhesion evaluations. These findings underscore the need for harmonizing standards and refining statistical methods—particularly by integrating rupture mode analysis—to enhance the reliability and accuracy of adhesion assessments. This study encourages using a more robust and consistent framework to ensure the long-term performance and safety of building facades.