The preservation damage of hydrophobic polymer coating materials in conservation of stone relics

The use of chemical materials to protect ancient stone relics is an effective method to prevent their weathering in outdoor conditions. At present, the typical materials for stone protection are mainly organic polymers, such as organic silicon compounds, fluorine-containing polymers and polyacrylates. These hydrophobic organic materials can play a protective role in the conservation of stone relics, but there are also some disadvantages. For example, the hydrophilic feature of stones and hydrophobic feature of organic conservation materials may cause stone damage by moisture expansion stress. In the present study, the damage mechanism of the interface between hydrophilic stone and hydrophobic conservation materials has been studied, including the effect of stone destructive factors: dry-wet cycles, freeze-thaw cycles and salt immersion. To prevent the damage by conservation materials, a multilayer method with hydrophilic bulk layer and hydrophobic surface layer is proposed. It is found that the multilayer method obviously reduces the degree of interface breakage. The reason is that there is a transition layer between hydrophobic and hydrophilic parts in the stones, which can disperse the stress of expansion and salt crystallization pressure near the interface.