Assessment of test methods for the durability of thermal mortars exposure to freezing

Thermal mortars are a trend in the construction industry in recent years, owing to the required decrease of the thermal transmission of building envelopes. The high porosity of thermal mortars leads to permeability values that can affect their durability since it creates more favourable conditions for the penetration of aggressive agents. Water is observed as one of the most common and harmful degradation agents. Regarding the climatic variability in Europe, freezing is a usual degradation mechanism both in severe and moderate climates. Since thermal mortars have higher water absorption than a common insulation, the freezing may occur. As no durability assessment methodologies to evaluate the exposure of thermal mortars to freezing degradation mechanisms exist, the present work has the objective to analyse existing accelerated ageing procedures, which envisage freezing degradation mechanism. As such, the durability assessment described in EN 1015-21 and ETAG 004 was adapted and implemented in different thermal mortars. It was observed that the higher number of cycles and the severity of the freeze-thaw ageing cycles, according to ETAG 004, may reproduce the effect of the northern European climates, while the ageing cycles, described in EN 1015-21, combine degradation mechanisms that occur in central and southern European climates. This adaptation allowed collecting reliable data and inputs to the development of durability assessment methodologies directly applicable to thermal rendering and plastering systems