Quantitative assessment of pre- and post-restoration weathering rates of limestone Mayan temples (Uxmal, Yucatán)

Abstract

The House of Turtles is one of the Mayan buildings of the Uxmal site in Yucatan. It has been erected during the Terminal Classic Period (AD 890-915), abandoned around AD 1050, and restored between 1969 and 1972. This monument was selected to quantitatively assess the impact of contemporary restoration practices on limestone weathering. Based on archival research and multi-scale photogrammetric surveys, weathering rates were calculated for two periods, covering respectively almost 1000 years (1050-2012) and 50 years (1972-2012). Whatever the spatial scale, whatever the construction choice, post-restoration weathering rates are systematically faster long-term rates: at the scale of the whole façade, stone recession has operated 38 times faster since restoration than on non-restored historical parts of the building (7.6 mm instead of 0.2 mm per century). This general trend is ascribed to the removal of the stucco coating that has protected limestone and delayed deterioration from the Mayan building times until the contemporary clearing and restoration operations. Another factor responsible for accelerated limestone decay is the replacement of wooden lintels by cement lintels, as indicated by the spatial distribution of deterioration hotspots on the façade and by the computed weathering rates obtained for six fine-scale windows taking into account the construction/restoration choices. This quantitative assessment leads to emphasise the need for softer, less intrusive restoration practices and conservation strategies, that should restrict the use of incompatible materials like cement and reinforced concrete, and consider stucco as a protective skin worth being maintained.