Gypsum-induced decay in granite monuments in Northwestern Spain

B. Silva Hermo; B. Prieto Lamas; T. Rivas Brea; L. Pereira Pardo

doi:10.3989/mc.2010.46808

Authors

B. Silva Hermo Universidad de Santiago de Compostela
B. Prieto Lamas Universidad de Santiago de Compostela
T. Rivas Brea Universidad de Vigo
L. Pereira Pardo Universidad de Santiago de Compostela

DOI:

https://doi.org/10.3989/mc.2010.46808

Keywords:

monuments, granite, gypsum, plaque shedding, stone decay

Abstract

One of the most common forms of decay in granite monuments is the detachment of the superficial layer of the stone (plaques, plaquettes and scales). Previous studies of granite monuments in the northwest Iberian Peninsula revealed a direct relation between this type of weathering and the presence of calcium sulphate, and a mechanism whereby the salt causes this type of decay was suggested. In the present study, various hypotheses as regards the origin of the gypsum found in granite monuments are proposed. The study involved analysis of the contents of ions soluble in water, the results of X-ray diffraction analyses and the ratios of CaO/SO₃ in samples of stone, mortar and deposits collected from different monuments. It was concluded that in most cases the gypsum originated from old paintworks or/and from the joint mortars, although inputs from other sources cannot be discounted, as discussed

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