Statistical analysis of test methods to evaluate rendering surface properties

Abstract

The objective of this study is to discuss the results of two test methods used to evaluate rendering surface properties: the superficial tensile strength (STS) and the pendulum rebound hammer (which provides the rebound index - RI), besides evaluating, additionally, the tensile bond strength (BS). The studied variables were the type of mortar (job-site mortar and dry-mix mortar) and the render moisture at the time of testing (in four contents). For each test, a minimum of 45 determinations was planned per analyzed situation, totaling 1411 valid results, which allowed a consistent statistical analysis and an in-depth discussion of the methods. The STS and RI tests were sensitive at a 95% confidence level to differentiate mortars from different strengths and were therefore approved for this evaluation. The most significant effect in all statistical models tested was the type of mortar. The variable moisture condition of the render was significant only for the results of STS and BS. In such cases, tests performed with wet or saturated renders presented much lower strength results compared to those carried out with air- dried renders. It was possible to obtain a significant correlation between STS and BS, with a high coefficient of determination.

Argamassas com resíduos para revestimento isolante térmico de parede pré-moldada de concreto

“…As prescrições francesa [33] e portuguesa LNEC 2005 [34] estabelecem que, para revestimentos externos, o valor mínimo deve ser igual ou superior a 0,30 MPa apenas quando as rupturas não são de natureza coesiva. Ou seja, a exigência de valor mínimo referese apenas a revestimentos que apresentam rupturas adesivas, que são as mais perigosas do ponto de vista de potencial para a patologia [35]. Ademais, a respeito dos resultados do ensaio de aderência cabe uma reflexão sobre as tensões que existem efetivamente nos revestimentos aplicados, às quais a resistência de aderência deve se opor.…”

Influence of capillary absorption and roughness of ceramic substrates on the adhesion of cement pastes

“…The heterogeneity of both ceramic and mortar materials is well known due to the variability in the raw materials used and the manufacturing methods used (RAMIREZ et al, 2021). This variability in material properties and variations associated with the test methods adopted to determine the adhesive strength affect the variability of adhesive strength (CARASEK; VAZ; CASCUDO, 2018;RAMIREZ et al, 2021;SANTOS et al, 2020;TORRES;VEIGA;FREITAS, 2018;VALENTINI et al, 2022;ZANELATO et al, 2019).…”

Reliability of in-situ diagnosis in external wall renders

“…External rendered façades are important elements of the building and significantly contribute to its in-service performance by playing a key role on the interior hygrothermal conditions [1]. In general, the main required render characteristics include adequate elasticity to prevent the formation of cracks due to movements, sufficient adhesion to the support without blistering, resistance to various climatic agents, suitable water vapour permeability in order to have a good in-service behaviour during the wetting and drying processes, and mechanical strength [2][3][4][5][6][7].…”