Multidimensional Approach to Evaluation of Weathering Degree of Lower Plant on Stone Cultural Heritage in Cambodia

The West Gate of Nokorbachey Temple, built by King Jayavarman VII in the Angkor period (12–13 c), is decorated with bas-relief on medium-grained sandstone. It is being damaged by lower plants such as algae and lichens, which inhabit the surface of the stone and produce organic acids, releasing minerals into the soil and causing physical damage when removed. The high temperature, humid climate and spore reproduction of lower plants make it impossible to completely solve the biological damage of stone cultural properties in Cambodia. Thus, it is necessary to collect data on biological distribution and activity through monitoring and establish scientific conservation measures based on the analysis. In particular, because damage by lower plants is a three-dimensional damage type that accompanies the corrosion of stone through biochemical action rather than simple biofilm formation, quantitative and qualitative evaluations were carried out in parallel. In this West Gate, the incidence rate of photosynthetic algae and lichens is close to 80%; however, the bas-relief showed relatively little coverage and vitality due to the role of roof shading. As a result, partial cleaning and consolidation of the two passage gates and the right area of the external side are required due to the high level of biological weathering.