Abstract: Brick heritage buildings in the hot and humid regions of southern China are exposed to coupled high-temperature and high-humidity conditions. Moisture retention within brick walls and cyclic crystallization of soluble salts jointly drive material deterioration and structural damage, posing persistent threats to the authenticity, integrity, and long-term preservation of these heritage buildings. The Site of the First National Congress of CPC is a Major Historical and Cultural Site Protected at the National Level. Focusing on its brick facades, this study integrates microwave-based nondestructive testing, microscopic observation, X-ray diffraction (XRD), and X-ray fluorescence (XRF) spectroscopy to systematically investigate the spatiotemporal distribution of internal moisture content and the morphological and compositional characteristics of surface salt damage. The results show that, during the monitoring period from February 2025 to January 2026, moisture content in both the south and east facades exhibited pronounced seasonal fluctuations, with peak values occurring in summer, particularly from June to August. Moisture content at the depth of 5 cm responded rapidly to short-term environmental variations, and the moisture distribution showed obvious spatial heterogeneity. However, moisture content at the depth of 10 cm exhibited a delayed response and remained generally at higher values. Salt-damage products were composed primarily of quartz, calcium carbonate, and sulfates. The brick material was accompanied by deterioration phenomena such as flaking and granular disintegration. It is essential for scientific and refined conservation of heritage buildings to develop targeted measures based on the deterioration characteristics and mechanisms at different facade areas.

Key words: revolution relics, exposed brick wall, water-salt migration, nondestructive testing, preventive conservation