A corbel is a course of brick or stone set out past the course below it, used to step masonry outward for a decorative ledge or inward to narrow a passage like a chimney's smoke chamber.
Each corbeled course typically projects only a small distance past the one beneath it, since stepping out too far too fast leaves the top courses unsupported and prone to cracking or shifting. A mason builds a corbel by shifting each successive course out a controlled amount, relying on full mortar coverage and the weight of the courses above to hold the projection in place. Corbeling shows up in a lot of places: chimney crowns and caps often sit on a corbeled brick shoulder, smoke chambers narrow using corbeled courses, and decorative brickwork uses corbeling for cornices and belt courses.
Corbeled brick depends on solid mortar bonds between every course to hold the projecting weight, so it's one of the first places freeze-thaw damage shows up as loose or missing brick. The stepped ledges also catch and hold water and snow longer than a flat wall surface would, which speeds up mortar breakdown at each joint. On chimney rebuilds we pay close attention to matching the original corbel pattern so repaired sections tie in visually and structurally with what's still sound.
More masonry vocabulary from the glossary.
The services where this term comes up.
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