This is a common problem that we can help prevent…… The white stains or powder-like material is often the result of water penetration of the chimney. During a rain, snow, or ice storm, water is absorbed by the brick and mortar crown. In the case of snow or ice storm the freeze thaw cycles can enlarge the cracks on the top of the chimney mortar crown allowing water to enter the structure this way. The chimney will soon saturate with water. As the chimney dries, lime and salts from brick and mortar are pushed out of the pores of the chimney. Wood that is in contact with the chimney can also absorb water, and in most cases, start to rot.