Ash can cause corrosion. Metallic roof surfaces, particularly older galvanized roofs that are pitted, and lower gauge galvanized roofs, are most susceptible to increased deterioration from ashfall. Fresh ash may have an acidic surface coating; and volcanic gas and aerosols, which frequently accompany an ashfall, may also contribute to corrosion. Atmospheric conditions such as rainfall, wind speed and direction, temperature and humidity also contribute to corrosion rate.
To prevent or reduce the accelerated deterioration of roof coatings following volcanic activity, roof surfaces should be cleaned up and/or protected.