Flemish bond

Virginia

By the early 18th century Flemish bond became standard for brickwork on refined colonial buildings, especially in Virginia. Important Virginia houses and churches made use of glazed headers to give a lively checkered effect to the wall surface. The use of glazed headers was a practice brought from southern England...

Glazing results from the way the bricks were stacked in kilns (or temporary kilns called clamps) for firing. The headers were positioned closest to the heat source and were thusly glazed or vitrified just as a piece of clay pottery would be glazed. A brick, after all, is a ceramic.

In colonial Virginia and neighboring colonies, brick kilns were normally fueled with oak. The potassium in oak produced a chemical reaction with the clay resulting in the clear blue-gray glazes on the headers, which provided a rich contrast to the red stretchers.

By the mid-18th century, the stands of oak in eastern Virginia were being depleted. Hence, softer woods, such as pine, were used to fire brick kilns. Pine does not produce the light blue glazes that oak does but instead turns out smutty black headers. Black headers were not considered attractive, thus when a wall was laid up in Flemish bond, the black glazed headers were laid facing inward and the unglazed headers were exposed on the wall surface. This gave the walls an overall even color ... Rubbed bricks continued to be used at jambs and corners but the color contrast was not as strong.

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Philadelphia

Glazed-header Flemish bond continued to be used in well into the 18th century. However, Philadelphia headers tend to be black rather than the light blue-grays of Virginia and Maryland. This is probably the result of firing bricks with wood other than oak. The black headers are a dominant element of Philadelphia’s Carpenters’ Hall, built 1770-73.

Regrettably, much of Philadelphia’s 18th-century brickwork was irreparably damaged by sandblasting during the city’s extensive restorations of the 1960s and ‘70s. Carpenters’ Hall fortunately was spared this misguided disfiguring; its brick surfaces and mortar joints remain in good condition.
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The use of Flemish bond experienced resurgence in the late 19th and 20th centuries, brought on by the popularity of the Colonial Revival and Georgian Revival styles.

- Calder Loth, Classical Comments: Flemish Bond: A Hallmark of Traditional Architecture (Online Dec. 2012)