Mies’s primary goal for the twin buildings was to express the logic of the towers’ structural skeletons on their facades. The supporting columns and spandrels provide the key organizing elements, with theelevations further subdivided by vertical mullions and then infilled with floor-to-ceiling windows. The buildings sit on a triangular plot of land, with their rectangular, three-by-five bay footprints facing each other at right angles. The glass-enclosed lobbies are pulled away from the perimeter columns, making the buildings appear to almost float on a shared travertine, plinthlike plaza.
Completed in1951, the buildings were Mies’s first realization of his vision for a glass-and-steel skyscraper. The pair, along with a handful of other midcentury projects, including Pietro Belluschi’s Equitable Life Assurance Building (1947), in Portland, Oregon, and Skidmore, Owings & Merrill’s Lever House (1952), in New York City, would become the prototype for postwar high-rise development around theworld.
The Lake Shore buildings have long been recognized as icons of Modernism. They were placed on the National Register in 1980 and designated Chicago Landmarks 16 years later. However, this status did not make either 860 or 880 immune to the not-so-unusual effects of exposure to the elements: After more than half a century of freezing and thawing, wind and rain, surface corrosion was readilyvisible on the towers’ gridded facades. At their base, the lobbies’ storefront system was badly deteriorated, pavers were cracking and spalling with water seeping into the below-grade garage, and rusted exterior lighting fixtures left the plaza underilluminated.
To return the buildings to their former pristine Minimalism, in 2007 the owners, the 860-880 Condominium Association, tapped amultidisciplinary team of Chicago-based consultants headed by Krueck & Sexton Architects. The firm is primarily known for its own sleek designs, rather than preservation work, but had earlier completed the restoration of Mies’s S.R. Crown Hall (1956) at the Illinois Institute of Technology [Architectural Record, January 2006, page 148]. At Lake Shore Drive, as with Crown Hall, the challenge was to improveperformance, but in way that respected Mies’s stark aesthetic. The fundamental issue, says Krueck & Sexton principal Mark Sexton, FAIA, “was making a historic landmark better while preserving the original design intent.”
Work on the approximately two-year-long project started with forensic consultants from Wiss Janney Elstner (WJE) thoroughly documenting the condition of thetowers’ coatings. They found chalking, corrosion along the edges of the steel mullions, and isolated areas of blistering and craters. The problem was in part due to so-called “mill scale” — a layer of oxide that forms on rolled steel or iron during the production process. Typically, this substance is removed as part of normal surface preparation to improve adhesion, but at 860-880, workersapplied the original coatings with the mill scale still intact, explains Arne Johnson, a WJE principal. “These were the first exposed steel frames in Chicago,” he says. “Everyone was still learning.”
With the understanding that the towers had been repainted as recently as the late 1980s, the owners and the restoration team considered sandblasting to remove the mill scale, the original lead-based...