[ardecila]

Should qualify that statement about mortar - LVDW's correct if your wall is the typical Chicago common brick, or even most historic face brick. It sounds like that's probably the case since you're in a landmark district. But modern brick from the 1940s or newer is much harder and fired at higher temperatures, so a modern mortar mix is appropriate.

Also, being in a landmark district may increase your risk. The risk of nosy neighbors calling the city on you goes up dramatically in a landmark district... you'll probably be OK still, but just be aware. Masonry repairs are usually an Easy Permit which isn't too hard to get but you also need an Air Quality permit for grinding/sandblasting activities, which is a little tougher (need to notify your neighbors formally, etc).