SEPTEMBER 10, 2002 -- Inspired as much by the rocky earth as by De Stijl, Bauhaus, and Richard Neutra, Frank Lloyd Wright emerged from a decade of near-dormancy in 1935 to design Fallingwater, a home in rural Mill Run, Pennsylvania. It was worth the wait; the icon of American design would produce what is arguably the most important and recognizable private residence in the world.

The very genius of Wright's work, however, has made the house a maintenance nightmare: the 7,000-square-foot plan is half terrace, much of which extends over a lively cascade; reinforced concrete was something of a novelty at the time, and massive cantilevers like these were unheard of. Every detail seems to taunt the very natural forces that Wright sought to emulate. He liked rolled roof edges and intersecting planes of materials, but he disliked visible counterflashing and corner window mullions. The result celebrates nature while thumbing its nose at the entropic physics of flowing water, erosion, and gravity.

A horror to maintain, perhaps, but this ingenious assemblage and its aggressive siting also make it a conservator's dream. For someone like Pamela Jerome, senior associate in the preservation department at New York City-based Wank Adams Slavin Associates, it's a delightful opportunity to both wallow in history and redeem it as well.

In spite of many restoration campaigns over the decades, by 1995 the condition of the house was enough of a concern to the Western Pennsylvania Conservancy (WPC) to merit a thorough study of the sagging cantilevers, corroded steel, and water-damaged painted stucco. Unlike past repair projects, says Jerome, this large project would allow the preservation team to consider the building holistically, rather than on a piecemeal basis. "It's a stabilization project and the most minimal intervention possible," she says, while admitting she has approved some changes to Wright's original detailing. "We try and save as much of the original, authentic fabric of the project as possible."

Concerns about the integrity of the main cantilevered terrace-which, it was learned, also supports the master bedroom terrace above by means of four T-shaped steel window mullions-led to a campaign of nondestructive testing of the reinforced concrete. Using radar and ultrasonic methods, engineers at Robert Silman Associates verified concrete conditions and reinforcing bar sizes, and later installed an exotic system of "crackmeters" to determine whether visible gaps in the slabs were growing. In fact, they were.

Encouraged by the engineer, the WPC allowed the installation of temporary steel shoring on the streambed below the main cantilever to avoid catastrophe while the designers planned a structural rescue. The solution would require removing the terrace and living room flagstones and drilling holes in the slabs to insert a system of ducts threaded with steel post-tensioning cables. By tightening the assembly, Wright's 65-year-old terrace would be fortified with positive bending moment.

The original terrace structure resembles an upside-down coffered ceiling; concrete beams and joists sit on top of the slab, which rests atop concrete bolsters and rock outcroppings. To connect the new wire bundles to the structure, says Silman's John Matteo, the Baltimore-based post-tensioning contractor VSL poured concrete blocks on both sides of the original concrete beams and ran the duct through holes in the joists. VSL then applied a compressive force to the beam-block assemblies to transfer force as it cranked up the cables. In a dramatic instant, Matteo recalls, old cracks in the parapets vanished and patching stucco added over the years buckled; the cantilevered terrace lifted imperceptibly away from its shoring crutch.

Two more noteworthy if less exciting structural interventions await, says Lynda Waggoner, the director of the WPC who has been overseeing the restoration work since 1986: An upper-level terrace cantilever will receive carbon-fiber strengthening, and an elegant staircase hanging down to the stream will see its steel straps overhauled. Still, she explains, the meat-and-potatoes of Fallingwater's preservation work has been dealing with water infiltration and its effects on concrete and plaster surfaces, paints, and stone masonry. "The building is designed in such a way that it does not shed water easily," Waggoner notes.

Working with Norman Weiss, a noted analytical chemist and masonry conservator, Waggoner and Jerome began studying solutions to some of the thornier materials issues-and the unintended complications of previous repairs. For example, while Wright left the terraces without counterflashing for aesthetic reasons, an upgrade about 30 years ago introduced lead flashing. The fix might have worked for a mansard roof, but not on a balcony where the malleable sheets are bumped and kicked by scores of visitors each day; copper flashing ultimately replaced the lead.

To protect the flat terraces, Jerome's team specified an inverted roofing-membrane assembly to allow drainage; for the flat roofs, a three-ply built-up roof of modified bitumen is covered with a local golden-yellow pea gravel (matching the original specs) that helps the planes visually blend in with the concrete. Because the rolled edge is exposed and there's no thermal break at the slab, the base sheet was made a venting layer to alleviate condensation on the top slab surface. To protect interior surfaces, ceilings are painted with a vapor barrier-a low-moisture-transmission primer-and then latex paint.

The conservation team is testing paints from four manufacturers for the stucco and concrete surfaces. For the rolled roof edges, the team is testing an acrylic elastomeric formula to paint the base flashing. The growth of microorganisms on horizontal surfaces makes it hard for most paints to stick; test samples were applied in June and September for evaluation next February. The first coat for the interior walls is an alkali-resistant primer, followed by a low-odor, zero-VOC latex. The walls will have a slight texture, not the gritty look that was added during past renovations.

The next phase of the work, explains Waggoner, entails restoring the stairs that hang below the main cantilever, running from the living room to an ice-cold plunge below. The glazed hatch to the stairs, which was completely corroded, has been repaired by John Seekircher, a specialist in steel window repair.

Unsurprisingly, the steel straps supporting the stairs below had corroded, causing the concrete to spall. Using "Black Beauty"-a blast-cleaning mix for steel and iron made of coal slag-the team exposed the bare metal, and attempted to patch the areas with pourable and hand-troweled cements. The fix didn't take, says Jerome, and WASA and Silman are beginning a replacement project using stainless-steel straps. While Jerome was disappointed that the steel structure couldn't be saved, she takes solace in the fact that the stairs had already been rebuilt once after a flood. Elsewhere in the project, Jerome was able to bring the house even closer to Wright's original design and detailing by preserving shapes and profiles. At the rolled roof edges, for example, she abandoned the termination bars installed in 1987 that finish off the roofing membrane. "We added a bead of silicone caulk on the soffit side so there would be a place for water to drip," Jerome recalls. For the preservation-minded, this is infinitely preferable to cutting a groove into original concrete, which permanently alters the profile of the concrete. The silicone, like the liquid membrane and polyester fleece that terminate nearby, is a material that was unavailable to Wright in 1935. But the details work because they are silent-the same colors, the same profiles-as the master builder's original intent. (integral)