Dubtastic is a great site for grunge effects. You may find brushes here. There also
might be tutorials. Explore this site. There is also another site
You will find many vbrushes here & tutorials on how to make a vbrush. This site is
down at the moment, but you can try it later or tomorrow. All the steps below I used
different blending modes, so you will have the play, until you find the look you want.