From Laboratory Formulation to In Situ Evaluation: PCM-Enhanced Lime-Pozzolan-Cement Mortars for Thermal Retrofit of Heritage Architecture

The energy retrofitting of heritage buildings is constrained by strict requirements on material compatibility, reversibility, and minimal intervention, limiting the use of conventional insulation systems. In this context, lime-based rendering mortars incorporating phase change materials (PCMs) offer a promising solution for enhancing thermal performance while respecting conservation principles. This study investigates the suitability of PCM-enhanced ternary lime-pozzolan-cement mortars through a combined laboratory and field-scale experimental approach, with particular emphasis on real-scale validation under outdoor conditions. Mortars incorporating microencapsulated PCMs were characterized in terms of microstructure, hygric and mechanical properties, thermal conductivity, and latent heat storage, alongside durability assessment under freeze-thaw and salt crystallization cycles. Thermal performance was evaluated using hot-box testing and monitored full-scale mock-ups exposed to real climatic conditions. The results show that PCM incorporation significantly reduces thermal conductivity (from ca. 0.63 to 0.30 W m−1·K−1) while providing latent heat storage up to 2.7 J g−1. Durability performance was maintained or improved compared to reference mortars. Both laboratory and field-scale results demonstrate the ability of PCM-enhanced mortars to attenuate temperature fluctuations, leading to smoother internal temperature profiles and reduced thermal peaks under real environmental conditions. Overall, the findings confirm that PCM-enhanced ternary lime-based mortars can provide passive thermal buffering while maintaining compatibility with heritage substrates, supporting their application in conservation-oriented energy retrofitting strategies.