Experimental assessment of lime-based mortars modified with eggshell powder and egg white – towards development of materials for repair of historic buildings

Abstract

In this paper, mechanically processed eggshells were employed as a partial replacement for silica sand in lime-based mortars intended for the repair of historic buildings. To ensure the workability of fresh mortar mixes on the control value, egg white was incorporated as a natural modifying agent. The introduction of these organic constituents aligns with current conservation and repair approaches, which prioritize material compatibility, reduced environmental impact, and a return to historically validated construction practices. The study evaluates the influence of ground eggshells and egg white on the fresh and hardened properties of the mortars, with particular emphasis on their mechanical performance, pore structure, thermal and hygric performance, and potential applicability in heritage conservation. Higher substitution ratios of fine silica sand with eggshell powder, namely 50 vol% and 75 vol%, made it possible to produce mortars with increased porosity, adequate mechanical strength, and high water vapour permeability, making them suitable for conservation and repair of historical masonry. The addition of egg white helped maintain the desired workability of fresh mortars. Moreover, it reduced water ingress by forming a hydrophobic layer of denatured proteins within the pore structure, which may consequently improve the mortars’ resistance to moisture-related deterioration processes.