Stack soil pipe issue

[Kezzo]

Hello all,

I've had a leak with the shower fitting which, which is now resolved. However I had to smash out some tiles to expose the piping. I noticed that my stack pipe is filthy, and wondered why it is has these rust trails (image 1 & image 2). I'm wondering if this is an issue, I'm guessing the pipe is cast iron. There are no rust trails further down the pipe though.

Second issue is that where the pipe meets the ground there are wet patches on the floor (image 3). I've had a plumber come out and check but he says all the pipes are ok, no sign of leakage and it is most likely condensation. The level of dampness in the floor varies from day to day (image 4). Does this sound very likely? There's another angle of the stack pipe and floor (image 5).

For context I live on a ground floor flat in a 4 floor building, the stack pipe in my bathroom that goes through all floors.

If any one could shed some light it would be greatly appreciated.

Thanks.

 

[Schrayder]

Its filthy and corroded because either it got wet years ago and no one cleaned it (why would you)
Or it is currently leaking and corroding (unlikely)
Either way, if you're worried about it, its a communal pipe and the freeholder / landlords responsibility.
If its not wet or leaking forgot about it, cast iron pipes in voids are never pretty.

 

[RandomGrinch]

It looks exactly the same as every service duct I've ever seen, in my place of work!