Action of Urine on Stone-Built Heritage

Abstract

Due to its resistance and durability, stone is the material most used in construction by humanity. The aim of this study was to investigate the action of urine on granites. Accelerated alteration tests were performed on Grey Itaquera, Pink Itupeva, and Black Piracaia granites – stones from the São Paulo State, Brazil, which were widely used in the historical built heritage of the São Paulo state. The test was performed with 30 cycles of partial immersion of nine samples in artificial urine solution and the sanitising of the specimens, totalling 60 consecutive days of testing. In the first 24 hours, the samples were partially immersed in urine; in the following 24 hours, the samples were sanitised in three different groups: A) without washing; B) washing with natural water; C) washing with a 5:1 solution of natural water with bleach. The alterations induced in the specimens were evaluated by spectrophotometry, P-wave velocity, and scanning electron microscopy. The main results obtained were chromatic alterations and crystallisation of salts on the three types of granite. The study concluded that urine is a substance that can cause moderate alterations in the aesthetics and structure of granitic stones.