•Thermal insulating mortars were exposed to different accelerated ageing procedures.•Ageing tests included elevated temperature, freeze–thaw and elevated relative humidity levels.•The ageing procedures were designed to be equivalent to 10 years of natural ageing.•The long-term thermal conductivity and mould susceptibility of the mortars are assessed.•A maximum increase of thermal conductivity up to 30% is obtained after ageing. The use of thermal insulation materials in the opaque walls is one of the best strategies toward the improvement of the thermal performance of the building envelope, thereby contributing to increase the energy efficiency of the built environment. In this context, an increasing number of studies are focusing on the development of mortars with enhanced thermal performance, i.e., thermal insulating mortars. However, considering the innovative character of these materials, reliable data on their long-term performance is still lacking, particularly concerning the thermal performance and suitability to refurbishment works. The aim of this paper is to evaluate the long-term thermal conductivity and biological colonisation of industrially produced and experimentally designed thermal mortars with EPS, cork and silica aerogel aggregates. The long-term performance of the mortars was assessed prior, during and after exposure to three accelerated ageing tests including elevated temperature, freeze–thaw cycles and high humidity levels. For each test, an empirical model (i.e., Arrhenius law, Peck model, and Coffin-Manson equation) was used to compute the acceleration factor, thus allowing to correlate the accelerated and natural ageing results and to estimate the degradation levels that would be obtained after 10 years of exposure to natural weather conditions. The results of the thermal conductivity show that a maximum increase of 10 % and 30 % can be obtained after ageing for the industrially produced and experimentally designed mortars, respectively. Moreover, all mortars were susceptible to mould growth, with the greatest biological colonisation levels obtained after the high moisture content ageing for the experimentally designed mortars.