Cover the floor under the wall with drop cloths to catch the plaster as you chip it off the walls. Cover any furniture in the room with drop cloths.
Hold the masonry chisel against the middle of the wall at a 45-degree angle. Gently tap the handle of the chisel with a hammer until you break through the plaster. Scoot the chisel over, under the cut you made, and hammer it across the brick until the piece of plaster falls off the wall.
Continue chiseling the plaster off the wall, moving from the middle of the wall across to one side and then the other side until you have chipped away all the plaster. Keep the chisel at a 45-degree angle or less so you do not gouge the brick.
Brush the wall with a wire brush to remove any small plaster pieces you did not free with the chisel. Fill a bucket with warm water and add enough dishwashing liquid to create suds.
Dip a nylon scrub brush in the soapy water and scrub the surface of the wall to remove the plaster dust. Let the wall dry before sealing or painting it. Remove the drop cloths and throw away the plaster pieces.