The effect of lime addition on weathering resistance and mechanical strength of gypsum plasters and renders

Despite historical evidence revealing the extensive use of gypsum-lime plasters and renders for interior, exterior and structural applications in many parts of the world, systematic studies of the effect of varying amounts of lime on the properties of these materials are rare. Here we studied the influence of lime addition (5-95 wt% quick-lime) on porosity, compressive and flexural strength, surface hardness, water vapor permeability and weathering resistance of gypsum-lime plasters in relation to their mineralogical composition, phase distribution, and textural characteristics. Results showed that even small lime additions resulted in reduced strength, but compatible conservation materials can be easily designed to match the properties of original historic plasters and renders, which are normally debilitated through deterioration. Moreover, lime additions significantly improved weath-ering resistance, thus enabling a wider use (including exterior applications) of gypsum-lime plasters, which could replace currently used building materials with larger carbon footprint in new constructions.

Automated summary

Despite the extensive use of gypsum-lime plasters and renders worldwide, there is a lack of systematic studies on the effect of lime content on their properties. Our study found that even small lime additions reduced strength but compatible conservation materials can be designed. Lime additions also significantly improved weathering resistance, enabling wider use of gypsum-lime plasters as a more sustainable alternative to current building materials.