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.

Just use red oxide primer like the steel suppliers do.

http://www.screwfix.com/prods/13032/...rimer-1Ltr-Red

http://www.decoratingdirect.co.uk/viewprod/t/TORQDRO/