Rust on steel posts

[moldy]

I noticed 2 of the steel posts have a rusty appearance (see attached photo).

 

They have since been primed without removing the rust.

 

Is that ok?

 

How long is steel expected to last?

[Conor]

If those steels are in the outside course of block work, they need to be either galvanised or bituminous painted.

[moldy]

  On 17/04/2021 at 09:02, Conor said:

If those steels are in the outside course of block work, they need to be either galvanised or bituminous painted.

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Does it need fire protection too? What's used for that?

[Mr Punter]

  On 17/04/2021 at 09:40, moldy said:

Does it need fire protection too? What's used for that?

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Probably not if they are inside the blockwork.  If they could be exposed to flame they normally have plasterboard, other fire rated board (like Superlux) or intumescent paint.

[Conor]

  On 17/04/2021 at 09:40, moldy said:

Does it need fire protection too? What's used for that?

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As they will be embedded in masonry that will have a high moisture content, they need protection from corrosion otherwise they will corrode and eventually (decades) fail. Your engineer would have specified this requirement.

 

No fire protection needed as they aren't exposed to a flame risk.

[Jilly]

I've got the same problem, but John Wayne has encased bits of the steel below the DPM without coating it, just wondering what to do, assume the cement needs to be chopped off. Rust has definitely appeared over this winter. 

[markc]

If steel is encased it doesnt need anything (think of rebar inside concrete). If its exposed then it can be either coated or not. Most new bridges are now left unpainted because it has been found that the rust layer protects better than deteriorating paint.

Edited June 3, 2021 by markc

[catrionag]

  On 03/06/2021 at 12:13, markc said:

If steel is encased it doesnt need anything (think of rebar inside concrete). If its exposed then it can be either coated or not. Most new bridges are now left unpainted because it has been found that the rust layer protects better than deteriorating paint.

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Agree. Picture above looks fine to me - just surface rust, and that will eventually form a protective layer that will stop any further penetration unless it's really exposed to the elements or you're right on the coast & getting salt spray

[George]

  On 03/06/2021 at 12:13, markc said:

Most new bridges are now left unpainted because it has been found that the rust layer protects better than deteriorating paint.

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That's only for alloys known as 'weathering steels'; in appropriate conditions the rust develops into a protective patina. It needs to be used carefully - particular attention to water shedding details and corrosion losses built into the thickness of the steel. It's a pig to weld, too. 

 

But agree on the post - surface discolouring isn't serious and once encapsulated, shouldn't corrode any more. 

[Tom]

Apologies for jumping in on this, can I ask about steels with exterior ICF walls? Our build has essentially a portal frame encased by ICF. The steels are 305mm wide so they will need to be rebated into the inner sides of the ICF blocks and so won't be entirely encased with concrete. Galvanised?

[Conor]

  On 03/06/2021 at 17:22, Tom said:

Apologies for jumping in on this, can I ask about steels with exterior ICF walls? Our build has essentially a portal frame encased by ICF. The steels are 305mm wide so they will need to be rebated into the inner sides of the ICF blocks and so won't be entirely encased with concrete. Galvanised?

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My SE has specified they any steel within the ICF core should be galvanised or painted. Personally, I'm not questioning it and I'm painting anything that isn't fully within the thermal envelope. Bituminous paint is cheap.

[Tom]

?roger that