On Thu, 13 Aug 2009 09:30:55 -0700 (PDT), sm_jamieson
wrote:

The RSJs holding up my upper storey have been exposed as part of
building work. They have slight surface rust (I'd say powdery 0.5mm
after 70 years) (web is 10mm thick) Not really going to affect load
bearing capacity, but it may be work painting them with something.
Hopefully wont need to clean them to fresh steel - that would be a
horrid job.
What should I slap on them to stabilize the surface ?
Cheers,
Simon.

I've used Hammerite No1 Rust Beater on a couple of cars and not bothered with
any further coats - though is both a primer and undercoat - and it has remained
in excellent condition, with no further rusting. I wouldn't hesitate to use it
in your situation, as it can be applied directly to rusty metal.

Andy C