Diammonium hydrogen phosphate (DAP) as a consolidant in carbonate stones: Impact of application methods on effectiveness

Abstract

New products such as diammonium hydrogen phosphate (DAP) have yielded good results as consolidants in construction stone used in the architectural heritage. Their effectiveness, which depends on the characteristics of the stone substrate and product concentration, is likewise impacted by the application technique used, which may or may not favour penetration into the stone. This study explored the effectiveness of brush, immersion and poultice application of a 3 M concentration of DAP on limestone and marble. Ultrasonic pulse velocity, colour change, porosity and pore size distribution as well as the variations in anisotropy, roughness and the alteration index were analysed to establish the efficacy of carbonate stone consolidants. Both stones were penetrated most deeply when the consolidant was applied with a poultice, while the pore structure of limestone favoured more intense penetration. Applying a poultice yielded good results in marble, improving its mechanical properties without inducing variations in colour or surface roughness. In limestone in turn, immersion delivered the best results, leaving colour unchanged while raising mechanical performance to levels similar to those for the unaltered stone.