The influence of different clay/sand ratios on the hygrothermal properties of earthen plasters in the Maijishan Grottoes

Variations in temperature and moisture content in the earthen plasters of the Maijishan Grottoes can readily lead to mural deterioration. This study investigates the influence of two different clay/sand ratios on the hygrothermal properties of earthen plasters in the Maijishan Grottoes. Two distinct types of earthen plasters samples were created with different clay/sand ratios: one with a weight ratio of 30:70 and another with a weight ratio of 70:30. The hygrothermal properties of earthen plasters samples were examined, and the temperature and moisture content variations were evaluated based on measurement data of hygrothermal environment in three caves. The findings revealed that the influence of the clay/sand ratios on thermal properties was relatively minor compared to its effect on hygric properties. Lower clay/sand ratio resulted in decreased thermal conductivity and specific heat capacity of earthen plasters, leading to increased temperature fluctuation, but the difference is minor. Additionally, in high-humidity environments, the difference in moisture content variations between the two types is greater than in low-humidity environments as the relative humidity changes. This research holds significant implications for the preservation of murals in the Maijishan Grottoes while also providing fresh perspectives for the restoration of multi-layered mural structures.