Studies of hair for use in lime plaster: implications for conservation and new work

Historic buildings constructed with lime plasters often require repairs and re-plastering of areas as part of a maintenance and conservation regime. Hair is commercially available for use in lime plaster and mortar, as it is still used today to provide additional strength and crack resistance to fresh plaster. In this study we examine commercially available imported hair from a number of species as well as fresh, untreated horse hair. Small angle X-ray scattering (SAXS) demonstrates a loss of keratin structure in most of the imported, treated hair samples, including horse hair compared to untreated indigenous horse hair samples. Fourier transform infrared spectroscopy (FT-IR) shows that the imported horse hair has high levels of cysteic acid present which is not shown in the fresh, untreated hair. The results obtained suggest that imported hairs are treated with an oxidising agent such as bleach or acid prior to sale, and this weakens the hair making it more susceptible to failure in a building context.