This study present most common phenomena observed on wall facades due to excessive rain in tropical climatic conditions such as Sri Lanka. The objective of this study is to understand the effect of materials properties and surface decay of walling materials.The most common walling materials such as brick, cement block, earth cement blocks and novel walling materials such as mud concrete block, geopolymer blocks were subjected to this study. And also, facade covering materials such as rough cement plaster and cement slurry plaster were studied. Intrinsic material properties were studied prior to natural rain erosion quantification. Basic engineering properties such as water absorption,capillary action,surface roughness, the compressive strength were studied. And then materials properties effect on surface decay such as water absorption, surface roughness was studied. Then a real world model was constructed and ten years of rain was simulated to understand the natural surface decay. And 3 scanner was used to quantify surface roughness and surface decay on walling materials due to natural rain. The results shows that, stronger materials and less surface rough materials are resistant to surface decay.Plastering is recommended to protect walling materials such as earth blocks to reduce the surface decay. Comparatively stronger walling materials are less prone to natural rain decay.However, cement plasters and cement slurry plaster covering is the most suitable materials for heavy rain.Cement slurry plaster is the most suitable walling covering for rain drop bouncing areas in outdoor walls in Sri Lanka.