Think I have worked out what the smell is. In some kind of vague spring-clean operation, a woman had been going around filling cracks and covering the base of the whole estate in thick grey paint. And it stinks. Maybe its an anti-infestation thing, I have no idea (and I am trying really hard not to mention the slapdash nature of the work).
I still need to find out more about how the whole post-Soviet housing situation works. With privatisation in the 1990s I guess many people - at least those officially registered in Moscow - were just handed over their flats. But now, how is maintenance paid for? Here, its a bit rough, but it seems to happen; I have been to other places where the apartment interiors may be beautifully done up, but the hallways and stairs are almost in ruins. And the stories about buying a flat, only to get into the (often fraudulent) quagmire around who owns and/or is registered to that particular apartment, are completely terrifying.