Reviving

A multidisciplinary team of consultants tackles the tricky restoration of a pair of iconic Chicago towers.
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From Architectural Record
Joann Gonchar, AIA

I-beams welded to the mullions emphasize the buildings' gridlike elevations.

Photo © William Zbaren

To return the buildings to their former pristine Minimalism, in 2007 the owners, the 860 Lake Shore Drive Trust, tapped a multidisciplinary 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 improve performance, 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."

Coating conundrum

Work on the approximately two-year-long project started with forensic consultants from Wiss Janney Elstner (WJE) thoroughly documenting the condition of the towers' 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, workers applied 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."

The restored storefront system incorporates cladding installed during an earlier renovation.

Photo © William Zbaren

As part of the renovation, the facades were repainted, restoring their graphite-black crispness (left). But before recoating, their surfaces seemed chalky (above).

Photos © William Zbaren (left),
courtesy Krueck & Sexton (above).

 

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 paint, and subsequent layers in their entirety. But after analysis showed that the existing coatings could support one more layer, they opted for a different approach that entailed more localized surface treatment, including removal of corrosion to bare metal and spot priming. After this work was done, contractors applied a water-based topcoat to the whole of both towers, restoring their graphite-black crispness.

Eventually, the towers will have to be entirely stripped and painted, but the restoration team contends that this more extensive work could be deferred to coincide with the need to replace sealants around window frames. "The sealant still has additional service life," says Ken Itle, WJE's lead architect for the 860-880 project. "Both [should] be done together," he says.

 

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Originally published in Architectural Record
Originally published in June 2010

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