A Chemical Approach to the Selection of Soils for the Reproduction of Earth-based Mortars for Conservation Purposes: Case Report from a Brazilian Historic Site

Abstract

Earthen buildings frequently demand the use of protective renders and plasters that should be, in several aspects, compatible with the underlying structures. To this end, earth-based mortars have traditionally been used and are common in historic houses. Their periodic replacement or repair is inevitable and intrinsic with their naturally sacrificial role, but restorations are also expected to follow suitability criteria, as well as minimum performance standards. In this paper, an approach to the reproduction of wall-finishes close to the original formulations found on historic buildings is proposed and described using the case study of a historic site in Brazil. The problem was addressed using the elemental composition data of a set of original mortars and a bank of local soils that were treated by multivariate statistical analysis. The final restoration mortars, that were obtained also by adjusting their granulometric profile by means of the mixture of sand, exhibited satisfactory performance in terms of adhesive strength and water absorption, as well as of resistance to water erosion when stabilized with lime.