Damp bridge through cavity wall?

[JT101]

We were instructed to fill the cavity wall around the steel where it sits in the cavity with strong mortar (sharp sand & cement 2.5 : 1), since the steel hadn't been galvanised, and this would protect it from corrosion.

DPC lined both the outer leaf and the steel beam to prevent transmission of damp through the concrete.

However, someone didn't think, and put cavity ties, obstructing the DPC. So slits were cut in the dpc to get it into the cavity.

They don't run all the way up, but might have two thin strips (5mm x 500mm) where the mortar is bonded to the outer leaf.

See diagram here:
http://www.thebreadcrumbtrail.org/g.../Eco-Living/Building-Failures/20140405_154542

So the question is, how does damp actually work? Would enough pass through these thin strips, bridge across the mortar, and spread into the inner leaf.

I've got a feeling it would, but no experience in this field. Perhaps it would take a long time and saturate the whole mortar first.

Other than starting over, what's the quickest fix, other than tearing the wall down?

I should mention, exposure to the elements at this point of the house is relatively low

 

[tony1851]

It will rust eventually, and concreting like that is pointless - the concrete will shrink (particularly such a strong mix like that) and damp will get into the hairline crack which will form between the steel and the dpc. Once in there, it will stay and work its mischief.

But it will ultimately not be such a big issue. It looks like a UC section (203x203?) and if so, the flange will be at least 11mm thick, which will take a long, long time to rust to the point where strength is compromised.

So I would say the cut in the dpc is neither here nor there and in the long term will make no difference.

 

[JT101]

Given the acceptance that this is a problem, I decided to go ahead and repair the whole thing.
I cut a hole on the wall, which gave me access with a hammer drill. I chiselled away the bottom of the mortar to firstly check if there was indeed a wall tie, and a split in the dpc. I then cut back the DPC to the split.

Better safe than sorry. In reality it's not such a big job if you just crack on with it, and saves a lot of heartache to remedy damp issues later