CoronaBlackWallWithSmudges

Hello there! Can anyone tell me or show me how can I create this black wall material?

Hi,

Wrom what i see, there’s probably not much more than solid dark colour in diffuse and some grunge texture in glossiness to bring variations to reflection.

I am having some problems on this thing. The grunge is not visible at all, what should I do? I made a rendering some time ago and I almost got that effect but now idk what is wrong.