The brothers Benedict and Enos Lapham, manufacturers from Scituate, bought the mill buildings on the east side of the Pawtuxet in 1851, enlarged them in 1861, and finally virtually replaced what existed before by the four-story existing building in masonry with a corbeled brick cornice. Horace Foster, a well-known mill builder, served as supervisor of construction for the owner-designed mill. Except for the way in which it is elbowed into a curve of the river, it is not among Rhode Island's most compelling mills visually—and what quality it once had has been all but destroyed by recent, utterly incongruous one-story additions. But the mill is also interesting for its 14.5-foot-high arched dam. These are rare in Rhode Island, where dams are mostly gravity barriers that cut straight across the flow. High banks (here artificially heightened) and rock that is suitable for abutments, however, allow an arched form, which can be thinner because its curved ends thrust into natural rock in line with the flow. The visual result is a pretty horseshoe falls. Following the deaths of the Lapham brothers and an interval under another owner, the Lapham Mill came under the control of the Knight brothers in 1903—their final acquisition. They enlarged the facility and eventually converted it, in 1920, into a major producer of book cloths, until the company's collapse in the mid-1930s.
When Enos Lapham built his mill he pushed to one side one of the oldest mill buildings in the area, converting it as a warehouse. This, known as the Green Mill because of its original color, exists in dilapidated condition east of the main plant on the edge of what is now a parking lot. For historians of technology it may be more significant than the big mill. It is a long, two-and-one-half-story clapboarded structure with a high, windowed, rubble basement on the side away from the parking lot. It has lost its sheathing on one side, revealing its structure as an an irregular grid of timbers with brick infill, each square irregularly punched with its window. How long it can survive without care is questionable, but it is an important relic of Rhode Island's earliest industrial past.