Protect your bumper’s backside
What is the best way to treat the back of a chrome bumper that has started to show surface rust. It is nothing bad, but is it better to paint the back of the bumper or to treat it with something like Fluidfilm, which is a spray-on product.
I have not used Fluidfilm— which contains an extract of lanolin, by the way—so I can’t comment on it, but I have had great luck using Rust-Oleum for that job. Rust-Oleum contains fish oil, and that somehow stops rust. The stuff was developed in 1921 by a sea captain who noticed that fish oil prevented rust on his decks. The military has used it for years with great success.
Clean the back of the bumper with steel wool and a little Naval Jelly being very careful not to get the Naval Jelly on the chrome itself because it could discolor it slightly. Once the bumper is clean and rust-free, you can use rattle cans to shoot on a coat of Rust-Oleum primer as well as the finish coats.
Let the primer cure, and then apply a tack coat of the color you want on your bumper. Let the tack coat get sticky (about 20 minutes) and then shoot on a finishing coat or two, letting the paint dry between coats. I have either used black or silver depending on whether the bumper was painted originally or not. One car I restored in 1983 had its bumper backs coated with Rust-Oleum and they still look as good as new.