In 1949, Mount Pleasant sustained yet another major campaign of construction, this one undertaken by the new owner, Fritz von Schilling. This work included demolition of the mid-19th-century frame wing and dismantling the old period III east wing foundation down to grade. Thereafter, new wings of brick were added at both ends of the house, and the roof was entirely re-framed. A new Colonial Revival porch and frontispiece (both of the Ionic order) were created on the river-front. At the same time, curving flights brick steps were added to the land front, embracing a fishpond, and new moldings were applied to the paneled jambs of the doorway remaining from 1901.
Inside, all-new finishes were added over the 1901 plaster, retaining the extant stair, most of the flooring, and the land-side exterior doors. The 1901 interior doors were also reused, and early chimney pieces arrived from remote locations to be installed in the west wing and in the east rooms of the first and second floors. On the second floor, 1901 subdivisions in the main rooms were undone, and closets were added in all three upstairs rooms. Bathrooms were provided in each of the wings and an appendage was created at the far end of the new east wing to house entry, storage, services and access to the cellar.