Use a Trisodium Phosphate Solution to Remove Paint From Brick. In a clean bucket, mix in a 2:1 ratio of one-gallon warm water to one-half cup trisodium phosphate (TSP). Using a long stir stick, mix the solution until all the TSP has dissolved. Using the stiff brush, apply and scrub the TSP solution onto the brick.
The only way to completely and safely remove paint from brick is to use a caustic paint stripper. Paint stripper is a thick paste that is applied with a brush or putty knife. After covering your brick with the stripper, layer plastic sheeting over it to adhere it to the brick. Then, wait at least 30 minutes before peeling the sheeting off.