Lime kilns are a common element of the rural landscape in the limestone-rich regions of New Jersey. Though the evolution of industrial production techniques caused their rapid abandonment during the early 20th century, many of these structures have survived in areas of limestone outcroppings, most prevalent in northwestern New Jersey.
Lime was and is a fundamental ingredient in mortar and plaster, and has been used for a wide variety of building purposes since early human history. Lime has also been used prevalently for agricultural purposes. Early in the 19th century, Thomas Jefferson promoted “scientific agriculture,” including fertilizing with lime. While sea shells were harvested for lime in coastal areas, limestone was used throughout the inland and upland regions of New Jersey and other states.
Following the centuries-old practice of lime “burning,” masonry kilns were constructed in the proximity of the end users of the material. They were often built as embanked structures of native, rubble stone with arched openings at the bottom of the primary wall. This allowed for ease of loading hopper-like openings at the tops of kilns with quarried limestone, and control of the fire at the base. Kiln firings burned the carbon dioxide off the stone, producing calcium oxide powder, or “quick lime.” This very caustic and unstable material was then mixed with water to form slaked lime or lime putty. The slaked lime could then be transported and spread on farm fields, or mixed with aggregates like sand to produce mortars and plasters.
Early kilns, known as set kilns, are smaller structures built into the sides of hills. They operated independently, producing small amounts of lime for the owner and immediate neighbors. As demand and transportation opportunities grew (canals and railroads), commercial kilns, known as vertical-draw kilns, which produced a large quantity of lime, were built. Many independent and commercial kiln examples survive, relatively intact. An impressive commercial example consisting of four kilns of stone and brick, and vestiges of supporting structures, associated with the former Windsor Lime Company, is located in the Borough of Hamburg, Sussex County. Another remarkable example can be found along the Delaware River and the Belvidere-Delaware Railroad track just north of the village of Carpentersville, in Pohatcong Township, Warren County. It is one of the largest groups of historic kilns known to exist in New Jersey. Encouragingly, the owners of this resource have sold a conservation easement on land including the kiln to the New Jersey Conservation Foundation, but protection from development alleviates only one of the overarching threats to the survival of this kiln and others.
There exist multiple significant threats to these unique relics of our industrial past. First and foremost, the abandonment of lime kilns halted maintenance procedures and the removal of vegetation. Water infiltration through the masonry and freeze-thaw cycles in the winter causes ice jacking and other damage. Expanding root systems of vegetation can pry the kiln walls apart and displace their footing. Damage from tree roots is one of the major causes of kiln collapses.
Additionally, vandalism has long threatened abandoned kilns. Often located in rural, somewhat isolated areas, the structures that have been compromised can become targets of vandals desiring to reuse the cut stone in new construction and landscaping.
Often, the owners of lime kilns do not want the liability associated with the structures, which may include safety concerns, property tax liability, and maintenance costs. Insurance companies are often reluctant to cover them, and owners are concerned that someone might be injured while on or near a kiln, or by the collapse of loose stone.
Lime kilns exemplify a category of cultural resources that often presents a challenge for preservationists. What options exist for significant historic resources that, by nature, are not necessarily candidates for continued or adaptive use? How can we better recognize and preserve these geographically diverse, yet interconnected, resources? Interpretive signage is one answer, of which there is a fine example at Stephens State Park in Mt. Olive Township, Morris County interpreting the set kiln there. Literature, such as the pamphlet “In Search of Lime Kilns in Warren County,” published by the Warren County Historical and Genealogical Society, and recognition, such as the recent local effort of the Hamburg Historic Preservation Commission to designate a local lime kiln Historic District, also helps raise the profile and confirm the significance of these unique structures. Thorough documentation and investigation of both the above-ground and below-ground components of these cultural resources should also be prioritized.
Lime kilns are significant historic resources that represent our agrarian, industrial, and architectural heritage. They were at one time a key component in the growth and building of our society and can continue to serve as educational tools. They are interesting, picturesque structures that serve as visual landmarks in their communities and are deserving of greater statewide interpretation, appreciation, and understanding, as well as stabilization and protection whenever possible.
Michael J. Margulies, AIA
President, Pohatcong History and Heritage Society
Marguerite L. Nemeth
Borough of Hamburg Historic Preservation Commission
(973) 827-9230, ext. 10