I want to build a structure onto my house made of heavy-duty angle iron. What is the most maintenance-free way of treating or painting steel so that it will be best protected an resistant to rusting? I would use galvanised steel, except that I already have a bunch of suitably sized (ungalvanised) steel beams, so I'm thinking of using thise. The beams are not badly rusted. In fact much of the orginal grey promer is still in place, even though the steel has been sitting in my outhouse for over 25 years.
I livenear the sea so the air is particularly salty here and things do tend to rust badly if not suitably protected.