 maybe that chimney's been there 35 years and the mortar's cracked and it's got water in it it froze it cracked some more you know what i'm speaking of and it doesn't take much of a crack or maybe some of the mortar's actually falling out you can get your finger into it and you get a hard driving rain water gets down in there and it continues and continues and continues efflorescence starts on the outside of the chimney so it's telling you