The effect of water absorption and type of substrate on the performance of rendering mortars in the fresh and hardened state

Abstract The main purpose of this study was to evaluate the impact of the substrate type and water absorption on the properties of rendering mortars. A mortar was applied on ceramic and concrete blocks and on standard concrete substrate, which received superficial treatments with water repellent and silicon. This strategy was used to alter the water absorption without changing the roughness. The mixture, application, and cure of the mortars were kept constant, and the results indicated that there are considerable differences in the spreading and open-time of mortars depending on the surface treatment and substrate type; there were no statistical differences in the adhesion or permeability of mortars applied on the ceramic and concrete blocks, regardless of surface treatment, but the values were much lower than those observed on the standard concrete substrate; and even with a direct influence of the coefficient of water absorption on adhesion and permeability, a different tendency was observed for each kind of substrate, indicating that, while absorption is important, it is not the main variable influencing the performance of coatings.

摘要 本研究旨在评估基底（substrate）类型与吸水率对抹灰砂浆（rendering mortar）性能的影响。将砂浆施用于陶瓷砌块、混凝土砌块及标准混凝土基底，并对上述基底采用防水剂与硅基材料开展表面处理，该策略可在不改变基底粗糙度的前提下调整其吸水率。砂浆的配合比、施工作业与养护流程均保持一致，试验结果显示：砂浆的铺展性与可操作时间（open-time）会随基底表面处理方式及基底类型的不同而存在显著差异；无论采用何种表面处理方式，施用于陶瓷砌块与混凝土砌块的砂浆，其粘结强度与渗透性均无统计学意义上的显著差异，但该两项指标的数值远低于施用于标准混凝土基底的砂浆；尽管吸水率系数会对砂浆的粘结强度与渗透性产生直接影响，但不同基底对应的变化趋势各不相同。这表明，吸水率虽会对砂浆性能产生一定影响，但并非影响饰面涂层性能的核心变量。