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YYePG Proudly Presents, Thx for Support

New frames and tops are in place, awaiting installation of the glass (above). The difference between the original detail (top right) and the new one (right) is very subtle.

1/4-inch glass

5/8 x 1 1/2-inch steel stop

1 x 2-inch steel bar frame

5/8 x 1 1/2-inch steel stop

5/16-inch flathead screw

1/4-inch sandblasted plate glass

Exterior Interior WINDOW DETAIL: ORIGINAL DESIGN

Exterior Interior WINDOW DETAIL: ORIGINAL DESIGN

1/4-inch glass

5/8 x 1 1/2-inch steel stop

1 x 2-inch steel bar frame

5/8 x 1 1/2-inch steel stop

5/16-inch flathead screw

1/4-inch sandblasted plate glass

1/2-inch glass

5/8-3/4 x 1 3/8-inch steel stop with sloped profile, shop primed and painted. (typ)

5/16-inch flathead screw, shop primed and painted, set head in sealant bed. (typ)

1/4-inch glass

WINDOW DETAIL: RESTORATION DESIGN

The first task was to quickly shroud the entire building in order to contain dust from the lead-based paint that was to be sandblasted off all the steel members. "We divided the building into quadrants," explained Michael A. Tenuta, senior vice president of Clune Construction. "Sandblasting the steel was followed by an inspection, then more sandblasting, then repairs, then another inspection, then the first of three coats of paint. There was no float time, and there was a constantly roving punch list."

The sound of glass shattering

"Mies's design was experimental," explains Sexton. "At the time, glass technology was in its infancy, and there were few regulations. Mies relied on his intuition regarding size." The facade consists of two types of windows. The original upper panels were enormous and not tem-pered—9 feet 8 inches by 12 feet 9 inches—and only K inch thick. With no codes to dictate size and thickness at the time, Mies was free to push the known limits of engineering. His experiment had mixed results.

Great expanses of crystal-clear glass poured daylight into the studio and created the "barely there" effect he sought. However, "great expanses of glass have a tendency to break and fall out in strong winds," Sexton adds. (Anecdotal evidence suggests that no one was ever injured, or at least not seriously.)

In contrast to the perfectly transparent upper panels, the lower units were sandblasted, which provided some privacy for the students, but mostly it served to hide interior activity from view, and thus retained a pristine Modernist face to the public. However, the glass was sandblasted on the interior face. Sandblasted glass is porous and absorbs oil from fingerprints and the adhesives students used to mount drawings on the windows. Due to decades of unintentional damage, the lower units became stained and scratched. In addition, the building was subjected to ad hoc alterations and mandatory repairs between 1970 and 1977. In 1975, Skidmore, Ownings & Merrill (SOM) replaced all the glass, including the thin upper panels, which were replaced with /8-inch lites. Then, employing new technology for the lower panels, SOM

YYePG Proudly Presents, Thx for Support -L I

YYePG Proudly Presents, Thx for Support -L I

The contractor shrouded the entire building (above) to keep the dust from the lead-based paint from escaping into the environment. Students work at Mies-designed drafting tables in 1956 (left). Mies's grandson, architect Dirk Lohan, ceremoniously launches the restoration by smashing one of the glass panels.

The contractor shrouded the entire building (above) to keep the dust from the lead-based paint from escaping into the environment. Students work at Mies-designed drafting tables in 1956 (left). Mies's grandson, architect Dirk Lohan, ceremoniously launches the restoration by smashing one of the glass panels.

installed a laminated glass with a mylar interlayer to imitate the translucent qualities of the original sandblasted glass. Although the solution eliminated the staining problem, the result was more reflective than Mies's matte finish, and repairing the repair, as it were, presented a per-

ALTHOUGH THE SOLUTION ELIMINATED THE STAINING PROBLEM, THE RESULT WAS MORE REFLECTIVE THAN MIES'S GLASS FINISH.

plexing challenge for Krueck & Sexton.

Every solution seemed to create more problems. The first challenge, and the one that generated the most controversy, centered on the upper panels. First of all, the glazed area was too large by code (or common sense) to have the original /4-inch-thick polished plate glass replaced. To comply with the code, the architects could have simply specified %-inch tempered glass. Keeping in mind that Mies's details are deceptively simple, Sexton recognized that tempered glass could be less than perfect. "When glass passes through an oven during the tempering phase, it can develop the slightest surface wave from contact with the rollers," he explains. The waviness can sometimes be noticeable when viewing reflected images from a distance. This would be unacceptable to OM

even the most forgiving critic. TTO

Now, /4-inch glass doesn't have to be tempered, so Sexton was ™

confident that he could deliver a perfect surface. But, of course, every IN

solution yields a new problem. In this case, the problem was color. Iron ES

in glass gives it a green tint, so the thicker the panes, the greener the tint. -BL

Crown Hall was intended to have glass so clear as to seem barely there, ICH

which was possible with /-4-inch panes. The architects eventually found a a manufacturer that could make low-iron glass in such large sheets, in ^

order to achieve maximum transparency, high-fidelity light transmis- ¿j sion, and the kind of brilliance usually reserved for jewelry cases and ^

museum displays. GR

The 68 original lites of the upper panels were replaced with PPG £

Starphire (low iron) glass, and the cycle of problems and solutions con- i

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