Pack rust changes in volume

[ldeem]

I have a project where a building parapet has been lifted up about 3/8" due to pack rust between steel roof beams and there bearing plate. It's a masonry building about 90 years old. The parapet cap has leaked for years which has caused the rusting.

My question is once the water leakage has been fixed will the pack rust change in volume? In other words once the moisture source is eliminated will the rust process stop?

Remediating the rust is not an option. I am really trying to decide if the masonry will be stable or do I need to account for ongoing movement. I am aware of temperature and moisture changes of other materials but I don't know about the pack rust.

 

[racookpe1978]

No. It will not stop.

That is, the existing rust flakes and loose "packing" will only increase a little bit more. the steel under that rust will continue to rust, since you cannot completely isolate it from air and atmospheric water vapor. So what is there will stay about it same size - with of course zero.zero strength, and what's underneath the loose rust will corrode more and loose even more strength from the original beam.

Best is to stop the water flowing down - which you did. Then grind out or chipping-hammer or scrape out the loose rust, blast/blow out the particles remaining, then try to repaint and reseal the exposed metal. A rust-coverter may help: changes the loose particles to a more stable chemical. (phosporic acid I think is the active ingredient, but then you still need to seal over that.

 

[bridgebuster]

I agree with racookpe1978; it won't stop. There are a differing opinions on the solution to arresting pack rust as well as their effectiveness. Attached is an article on the subject, however, it's promoting a proprietary system.

I have a bridge project under construction; there are a number of pack rust repairs to built-up steel members. We called for a power tool cleaning up to 1" deep, followed by an application of an epoxy penetrating sealer, followed by a polyurethane sealant & backer rod, then the standard 3-coat DOT paint system. It'll be some time before this work actually starts and years before we know if it was successful.