A lot of the less expensive row houses were built with a cheaper brick that was soft and permeable. Formstone was added to protect the structures.

Never could figure out why our first home in West Baltimore was a brick row house with a very imposing door surround added in Formstone. I hated it in those days because the rest of the house had a sort of Colonial appearance and then this big, ugly gray fake door surround.

It goes in and out of style. For a long time people didn't want to do anything to change it because it was regarded as a sort of folk art thing like having painted screens or blue window shades.