<p>Earthen plaster is a commonly used traditional technique in geotechnical construction and has been widely applied in the grotto murals of northwestern China, exhibiting significant historical and cultural value. Due to factors such as rain and irrigation, water often infiltrates into the earthen plaster layer through the substrate or foundation. This water often carries salts, leading to the disintegration of the earthen plaster. However, the disintegration characteristics of such earthen plaster under water-salt interaction remain unclear, and there are few studies on the effectiveness of currently popular natural hydraulic lime (NHL) restoration materials in improving disintegration, which is detrimental to the subsequent conservation of the earthen plaster. To investigate the disintegration characteristics of earthen plaster, 9 plaster samples were prepared, and surface contact angle tests, disintegration tests, and microscopic structure tests were conducted. The results showed that when only Dengban clay was used as a binder, the plaster completely disintegrated. Adding fibers to the plaster could resist disintegration to some extent. Adding NHL improved the water-repellent properties of the earthen plaster’s surface, and 10% NHL prevented the plaster layer from disintegrating. Low concentrations of salt solution had no significant effect on the disintegration process in the short term, but long-term exposure to salt solutions caused new salts to form through reactions with the hydrates of NHL.</p>