Making this post so someone is able to search for it in the future since I was unable to find it on the forum.
Was doing a deck this past week where the patio chairs left rust rings all over the new deck boards. With this being untreated lumber It was not able to come clean with your typical deck cleaning products I use F-18 and F-8 to do the initial cleaning. Degreaser did not help either.
F-9 was able to get the job done so the secret is out F-9 on wood will remove rust if your hesitant about trying it I went with a 1-1 ratio in a pump up sprayer. 
