Rendering Matt Black Paint

[Caticuta]

Hi, when I apply the 'matt black paint' material it looks spot on for about a minute, it then starts to settle down and changes to a real flat black (doesn't look like paint). It's the 'bumpy effect I'm after, I've tried applying a texture but that also settles down once I render it.

Any ideas? I'm not too experienced with keyshot so I'm sure there's an easy fix!

Thanks guys