This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
193. For inside walls that are to be plastered, the mortar projecting from the joints is merely cut off flush with the trowel. All outside walls and inside walls, where the bricks are left exposed, should have the joints struck, as shown in Fig. 74, (a), where a shows the mortar joint, and b the bricks in the wall. This striking the joint is done with the point of the trowel, which for the purpose is held obliquely. This method makes the best job for outside work, as the water will not lodge in the joint and soak into the mortar, as it will when the joint is struck as shown at (b), Fig. 74. The second form, however, is the easier one to make.