Historic Structural Detail: Bricks and Blocks

by Don Friedman on August 8, 2016

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A view from a recent site visit. I like mechanical rooms – in this case, the electric service room – because they typically have little or no architectural finishes, so the structure is easy to see.

The wall is a specific pattern of alternating two courses of block and one course of brick. I knew the building was mid-1900s (it turned out to be 1953, once I got into the research), which meant that the block is actual cinder block. (Most of the time, when people say “cinder block” they’re looking at concrete block of some kind; cinder blocks were made with cinders as the coarse aggregate.)

The walls of this one-story building are twelve inches thick, as was visible at the roof and windows, which is three brick wythes thick. Standard dimension concrete- and cinder-blocks are two brick wythes thick and three brick courses high. Therefore, the wall consists of one wythe of brick as exterior veneer with the brick and block seen in the picture as the back-up. Veneer wythes need to be tied to the back-up: wire ties were not yet common at the time this wall was built, so the traditional method of brick header ties was used here. The header bricks are visible on the outside of he building and extend one brick wythe into the back-up, leaving one wythe behind to be filled with stretcher bricks. That explains the inside face as seen here: brick stretchers alternating with block.

Common bond usually has headers every six or seven courses. In this case, the two block courses are equivalent to six brick courses, so that the headers are located every seven courses exactly.

This wall is an intermediate step in the evolution from all-brick construction to wire-tied walls. In the modern type, there is no necessary link between the geometry of the veneer and the geometry of the back-up. In this transitional form, the veneer bricks and the back-up blocks have to be in lockstep so the headers can tie it all together.

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