Is EN459-1 fit for purpose in the context of conservation?

Natural Hydraulic Lime (NHL) binders consist mainly of portlandite, reactive silicates and aluminates formed from the reaction of crushed limestone, containing clays or other impurities, during calcination. By their nature these binders have a variable chemical and mineral composition, depending on the geographical location of the limestone extraction (initial composition) and the manufacturing process. The NHL (Natural Hydraulic Lime) classification, as specified in the EN459-1 standard, does not consistently give a representative evaluation of the mortar properties, resulting in similarly classified limes often exhibiting very different properties and behaviour thereby hindering the ease of user specification for mortars. A representative selection of binders was characterised using calorimetric analysis, XRD, XRF and particle size analysis. The varying proportions of reactive silicates and portlandite between the limes was used to determine the kinetics of the hydraulic reaction NHL binders. These properties were related to the chemical and physical properties of the binders. A relationship has been established between the chemical and physical properties of the binders and the NHL characteristics. These results will be used to validate a model predicting the long-term behaviour of NHL mortars for conservation interventions on heritage and historic buildings.