Oxidation on steel

Hey guys any advise I always wash steel buildings like shops and barns with my standard house wash mix sh+dawn+simple cherry.

But I have building that is heavily oxidized the owner already made wand marks with his pressure washer and then called me to clean it after realizing how long it will take to clean.

I’m just want any ideas of other cleaning solutions I.e citric acid? Or I’m wondering if 2-stepping like a truck wash would work?



Do you have any pictures?

Sorry no pic as of right now.