On 15 Aug, 00:04, "js.b1" wrote:
If after 50yrs+ there is just a dusting of rust, forget about it...
- Black rust is millscale and actually inhibits further rusting
- Paints like hammerite can trap moisture if cracked (unlikely on an
RSJ)
- POR is good, but forget welding to it, or mag-drill n bolt to it
either
- Rust converters work, but only to a very limited depth
- Red Oxide does not have lead, probably some other oxide

Typically if you want to protect structural steel you...
- a) 3M Clean-n-Strip disc to a shiny surface including pits
- b) media blast to a "sa2" bright shiny surface including pits
- Paint with zinc epoxy primer £50 or epoxy mastic £30

To touch up coated steel, use galvafroid...
- Real cold zinc primer, £15 for 250ml, extremely heavy
- Only works where zinc can directly contact steel not rust
- No abrasion resistance, but very effective

I'd rather put the money towards replacing guttering early, because
that can really leave a trail of problems.

Well I'll probably just leave it then. I'll just hoover up the small
amount of
loose dust on the flanges. I've just replaced the guttering as it
happens ... ;-)
Simon.