Steel Building maintance question

[Stan]

Like many, we have several old metal buildings that are very rusty.

Does anyone know a simple way to restore them?   I have been told if I paint over the rust it will bubble and peel.

[Jay]

Yes that's true. You need to stabilize the rust before painting, with phosphoric acid. This is sold under many product names, rust gone, naval jelly etc. but the active ingredient is phosphoric acid. You can find it in most any automotive supply store. The phosphoric acid through a chemical reaction, changes the rust (iron oxide) to a stable inert compound called iron phosphate. You can then safely paint it.

[Stan]

How can you tell when it is ok to paint after a treatment?   Is that the chemical that turns the rust to a black color?

Thanks, Stan