The brick and stone foundation walls and chimney bases in the cellar provide the strong underpinning upon which the Mansion stands. As with the framing, some necessary interventions, completed with modern materials, have proven to be unsympathetic to the original fabric of the house, slowly causing unintended damage. Masonry repairs will include:
1. Replacing modern “Portland cement” with a soft, lime mortar, like that used in the original construction. Masonry is comprised of brick or stone blocks held together by a binder called mortar. The brick and stone used during the 18th century were soft, and they required a soft mortar. The reason for this is when moisture infiltrates a masonry wall, it will eat away at the softest part, ideally the mortar, which can be replaced much more easily than brick or stone. The moisture in the Mansion cellar wore away the soft mortar (as it should have), but when repairs were made, instead of using soft mortar, hard mortar containing water-resistant “Portland cement” was used. This hard mortar was the standard type used for all construction during the 19th and 20th centuries, and so it was also commonly used to repair historic houses. It has unfortunately proved to be far too hard for the soft brick and stone of 18th-century buildings. Its water-resistant properties have forced moisture into the brick and stone, exacerbating degradation of these materials.
2. Replacing later brick piers. As the Mansion’s first-floor framing aged, it began to sag, a situation worsened by multiple generations of repairs. To shore up the sagging timbers, more than 30 brick piers were added in the cellar in the 19th and 20th centuries, significantly altering the appearance of the spaces. Once the framing and masonry repairs have been completed, most of these piers will no longer be needed and will be removed. Those that are still needed will be replaced by less conspicuous supports, bringing the cellar closer to its 1799 appearance.