Hello!

We are trying to get to the bottom of an on going issue with mysterious marks on our walls in a stairwell that leads up from our kitchen (thats in the basement of a back to back terrace) to our second floor hall way.

We've had issues with damp is the past however that is now fixed as we've had specialists come in and sort that out for us a few months ago.

The pipes aren't water pipes so it's not a leak.

Has anyone got any suggestions? The plumber, builder and my father in law are all clueless!