Restoring the Lyman Estate’s Bark Pit Greenhouse
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Last spring, masonry restoration work continued on the Bark Pit Greenhouse at the Lyman Estate in Waltham, Massachusetts. The restoration of this important structure has been in the works for years and we are glad that the bark pit will now be a showpiece for the estate and help tell the story of the early nineteenth-century Boston gentry’s fascination with horticultural innovation. Along with ongoing landscape work—some currently underway and some planned for the future—the greenhouse will be more accessible and inviting to all our visitors.
For the second year, students from the Student Conservation Association’s Massachusetts-based Historic Preservation Corp joined with Historic New England to work on the bark pit restoration under the direction of preservation mason Fabio Bardini of Florentine Renaissance Masonry and supervised by Historic New England’s Preservation Carpentry Supervisor Omri Nassau. The Historic Preservation Corps is a ten-month program that provides participants with hands-on training in preservation trades. Historic New England has partnered with Historic Preservation Corps for several years in both training and field work.
The bark pit at the Lyman Estate (ca. 1800), built for Boston merchant Theodore Lyman, is believed to be the oldest of the estate’s greenhouses.The structure is the oldest surviving example in the United States of a greenhouse type known as a “bark pit” that relies on decomposing tree bark placed in beds, or “pits,” as a source of heat. In addition to the bark pits, the greenhouse features a firebox and an interior horizontal chimney that provides radiant heat. A series of overhead sliding windows heat the interior through solar radiation. In Lyman’s time, the greenhouse was integral to the kitchen gardens that surround it. The estate’s gardener would start vegetables in the greenhouse to get a jump on the growing season and place partially submerged pots with pineapple plants and other exotic fruit in the bark beds to keep their root systems warm.
In keeping with our preservation philosophy, we were able to restore the deteriorated masonry in-kind with traditional lime mortar. Along with rough granite and brick, the building was originally built with lime mortar that would have been made on site. To do this, a mason would have mixed quicklime and local sand and slaked the mix by adding water (slaking is a chemical reaction between water and quicklime that creates lime putty, to which sand is added to make lime mortar). The Historic Preservation Corps students mixed raw materials in this exact way to create an authentic and durable mortar to repair the deteriorated masonry.
An analysis we conducted on the historic mortar also gave us an interesting bit of history. The mortar had natural cement in addition to pure lime. This helped us refine the date of construction and add to our understanding of the structure. We were able to source natural cement from the original quarry in Rosendale, New York, to incorporate into our mortar mix.
The Bark Pit Greenhouse restoration is an excellent example of how Historic New England’s preservation approach goes beyond building materials conservation. We were able to restore a historically significant structure and tell its story to a wider audience. We used traditional, accurate materials that are local, green, and sustainable. We were able to work with local craftspeople and train the next generation of tradespeople in the process. In addition to the hands-on work completed by Historic Preservation Corps students, students in North Bennet Street School’s preservation carpentry program visited the site and sat in on one of Fabio Bardini’s masonry preservation lectures. And we gained knowledge ourselves as craftspeople and preservationists that we can use at all Historic New England properties. Perhaps most importantly, we are close to making the Bark Pit Greenhouse functional once again for its original purpose—to grow plants. In doing so, we are helping to preserve it authentically and making it more likely that it will be cared for moving forward. We hope that restoring the bark pit as an accessible working greenhouse that is inviting to the public will ensure that it enjoyed for at least another two centuries.
Written by Omri Nassau, Preservation Carpentry Supervisor
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