 Maybe a metal brush on a drill so I don't have to scrub so hard with a regular brush. Now, anytime you get a stain on brick, it's really difficult to get it off because brick is so absorbative. Now, with this mortar splash that's gotten on there, I think what I would do first, because brick is also a bit soft, I would use a wire brush. You would pick one up at a home center or a hardware store. It's got a stiff wire bristle.