Can anyone identify this substance/mould?

[mouldy]

Has anyone seen this type of mould before? It's dark reddish/brown and seems to be seeping through the concrete and the skirtboards. Its predominantly in the bathrooms but has started to appear coming from the carpet after it rains heavily.

 

[Chuck]

The pictures aren't great but it looks a bit like iron oxide, possibly from corroding reinforcement in the concrete. It could be mould due to damp due to condensation but the link to rain suggests that you have a faulty (or absent) damp-proofing membrane.

If I'm right, it's not good news. If it were my building, I'd consult a Chartered Surveyor to confirm/correct my guess and get them to draw up a specification for the repairs, which are going to need a builder who is quite competent.

I hope I'm wrong and it turns out to be condensation. How is the room heated and ventilated?