Sorry for digging up an old post. Every barn on my farm has been sprayed with used oil about every 7 to 10 years, depending on how long it takes us to dig up enough oil. The newest barn I own was built in 1952. The oldest was here in 1894, unknown of how much older than that it is. There is no rot anywhere on anything. The only problems I ever have has been that the barns are outlasting the fountations. A few years ago I had to jack up one of the barns, dig around it, and change the block on the back wall. That was the new barn from 52. I'm still suprised I didn't kill myself jacking it from underneith. Only picked it up about 1/2 inch, but still made me real nervous doing it. That being said, if it ever catches on fire you will have a hard time getting the insurance to cover it due to you spraying a flammible liquid on it. Also when spraying it will get everywhere. It will become airborne and cover everything, and travel farther than you think. My house is about 500 or so feet away and it got hit bad, with little to no wind.