Clues For A Minor Mystery

We’re looking at the side wall of a small, 1920s industrial building in Brooklyn, with the front facade on the left. (Click on the photo to enlarge it.) The two street facades – the one we’re facing and the front – have some ornament constructed entirely of brick. The only non-brick masonry is the cornice cap in stone.

There’s what looks like a long vertical crack in line with the lower step in the parapet, five full brick lengths (40 inches) from the corner. I believe that’s the left edge of a filled-in window, although I can’t prove it with just the information in this photo.

The first reason I think it’s not actually a crack is that I’m stumped as to what caused it and why it’s so straight. The crack continues down to the bottom, running diagonally for the last 6 or 7 courses of brick (16 inches or more) but goes nowhere at the top. A force capable of creating a sharp linear crack like that would surely crack the brick at the top of the wall as well. There’s no evidence that the top of the wall has been rebuilt.

The second reason is more subtle, more based on brick masonry than on structural engineering. The brick pattern is common bond, where there’s am all header course every so often, with a number of stretcher courses between. The headers courses don’t line up on either side of the vertical “crack”* but they do line up below (where the diagonal crack is) and above (where there’s no crack). That seems like infill, like two separate campaigns of brickwork.

The last reason is that there are two horizontal lines associated with the top of the vertical “crack.” The first is in line with the top of the vertical, and consists of some faint irregularities in the brick joints. The second is five courses higher, and consists of a slightly wider and discolored bed joint. Those two lines seem to me as if they could be defining the bottom and top of a steel beam serving as a lintel.

A lot of field investigation starts this way, looking for minor discrepancies that might tell us something about what we can’t see. You have to like mysteries.

* As a matter of fact, left of the vertical “crack” the header courses are spaced one every six courses, while to the right it’s one every seven courses.