Durability of a lime-based rendering system exposed to different environmental conditions

Abstract

Durability of lime-based mortars is a very interesting topic with many unknowns. The paper deals with the influence of wet-dry cycles, freeze-thaw cycles and exposure to soluble salt solutions on the composite samples consisting of one stone layer and two lime mortar rendering layers. Rendering mortars were composed of lime-putty as a binder, using river aggregate of two different gradations (0/4 mm and 0/0,5 mm) and two different lime:aggregate ratios (1:3 and 1:1) for inner and outer layer, respectively. After reaching the age of 90 days, samples were divided into five groups. Three groups were exposed to five cycles of wetting and drying. One group was exposed only to the deionized water action, another to the 10% NaCl solution, and the third group to the 10% Na2SO4 solution used only during the first cycle of wetting. The fourth group was exposed to four freeze and thaw cycles, while the final group was used as a reference. The results show that exposure to the wetting and drying cycles using water lead to the increase of the mechanical properties of the system, with pull-off strength 5.3 times higher when compared to the reference samples. Exposure to NaCl solution lead to almost unchanged behavior, while exposure to Na2SO4 solution lead to degradation during the final cycle of wetting and drying. Similarly, cracks occurred in the final cycle of the freeze-thaw test. After the finalization of tests, visual examination, XRF, XRD and SEM analysis were performed on the chosen tested samples.