Introduction 

In historic preservation, aluminum 

windows are generally thought of as replacement windows, common since the 

1970s. Many people are surprised to 

learn that aluminum windows in buildings have been around since the 1930s 

and that numerous landmark buildings 

in the J 930s and 1940s prominently 

featured them in their design. After 

World War II, aluminum windows 

gained more widespread use in the construction industry and soon surpassed 

steel window sales. By the 1970s, they 

rivaled the dominant wood window 

industry, particularly in commercial 

and institutional construction. The 

historic significance of early aluminum 

windows is now being recognized and 

efforts are being taken to preserve and 

rehabilitate them. 

Aluminum windows actually appeared 

as early as 1912 for use in railroad cars, 

streetcars, and buses. The Union Pacific Railroad touted them in their modem streamlined trains for their "high 

efficiency as to weather tightness, great 

ease of operation, low up-keep costs, 

great strength and beauty." 

It was the modern look and appeal 

of aluminum that helped generate a 

market in the 1930s for aluminum 

windows in buildings, particularly in 

signature buildings and high-end projects. By 1932, the Aluminum Company 

of America (ALCOA) was running 

separate full-page advertisements in 

Architectural Record proudly featuring 

buildings such as the Cities Services 

Building in New York City with its 

2,652 double-hung aluminum windows 

and the Medical Center Building at 

Louisiana State University School of 

Medicine in New Orleans with its 570 

windows (see Figure I). 

Leaving no opportunity to chance, 

manufacturers began offering aluminum 

windows that mimicked Colonial-style 

wood windows with true divided lights, 

and also casement, projecting, and accordion windows to compete against a 

thriving steel window industry. A 1932 

advertisement for residential aluminum 

windows that appeared in the Architectural Record read: "It isn't a fad - it's 

just plain thrift to use building materials 

of Alcoa Aluminum ... Take casements 

for instance. Because windowframes, 

sashes and sills made by Alcoa Aluminum are non-rusting, they won't drip 

stain and leave unsightly streaks on 

adjoining surfaces . . . " (see illustration 

above). Over time, aluminum windows even took on their own design, in 

contrast to the appearance of wood and 

steel windows. 

Tech 

WINDOWS 

NUMBER 22 

Maintenance and 

Repair of Historic 

Aluminum Windows 

Kaaren R. Staveteig 

Technical Preservation Services 

National Park Service 

Historic aluminum windows should 

be maintained and repaired. In the 

event replacement is necessary, a 

new window should match the historic 

one being replaced in design, size, 

configuration, and detail. 
"""' ...... .......... Nno<\'ortc.e ... 

An.:hoo:.-:', o-~R..udI. 

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.."..., droaNt'-l ~c_wfloll· 

.nc~'" w,nj 19' •• d~.f ,,1,_ 

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Not a n ou nce 

of excess weig ht in these 

2652 double-hung windows 

made of Alcoa Aluminum 

\\'mdo", (ra.me:s a.nd &1 h nude of light, strong 

Alcoa Alununum save ton. of WC-lght In tbe 

new Ci ll~ ScrV1t:e BUlldmg. New York C ity. 

But wmrJow (r ... .mcs and lUll mad~ of Alcoa. 

Aluminum b.we odw:r lIDportiJint ;,advantages... 

'rhty ",",11 not f\l!it . 1bcy WIlt not aWn aOJOln A 

10g 6urfaCC'!l. EffectlVely bamng run, snow and 

alttt., tbey anow no \lo-eathu rcoctratlOO. Light. 

tough, uUr.1bJe-they ........ utiy ""mtain<d. 

i The v.,de adapubihty of Alcoa Alummum to 

: hulldmg producti l$ att~tl:J hy the l.uge n\lm .. 

her of lc~dmg rmnu(xtuf tr who regularly 

(abnc"" pro:lucu of tim bgbt. '''''''g lD<ui. 

POIIe$-'iCJ of many SpeclflC advantagea. these 

prod~hould command tbe attention ot 

archlue ... We WIll be ~J..d to .uppJy you WIth 

the names of m.;.nufactvreu of \\-'1nOow frames 

and NSh and otbo.!r bwldmg product mWc or Alcoo Aluminum ALll MINUM COMPANY gf 

AMERICA; '1.4(" Oiiwr BUIlding. MTTIIIt.1RCI1, FA 

, 

THE BEST WINDOWS ARE MADE O F 

ALCOA ALUMINUM 

Figure 1. In 1932, 

Architectural Record 

magazine ran an advertisement for ALCOA 

Aluminumfeaturing the 

2,652fixed, doublehung and casement 

aluminum windows in 

the newly constructed 

Cities Services Building in New York City. 

The ad touted the 

wide adaptability of 

aluminum in building 

products. 

Whether a distinctive part of a ma- employed much heavier gauge aluminum than is used today, particularly 

with commercial and better quality 

residential windows. Some of the commercial grade aluminum windows also 

utilized steel for the sub-frame or for 

the connection to the wall opening, because of its greater strength. The steel 

sub-frame usually had welded corner 

joints to provide a continuous frame. 

Windows with steel sub-frames also 

commonly featured steel sills and/or 

mullions. 

jor architect-designed building or 

representative of an early use on a 

vernacular building type, aluminum 

windows from the 1930s to the 1950s 

have earned their place in the history 

of building construction in the United 

States. Today, they merit consideration 

for preservation and repair when dealing with historic buildings. 

Early Fabrication 

Most early aluminum windows were 

designed either to look like wood or 

steel windows. Their fabrication borrowed heavily from both manufacturing processes. In fact, a number of the 

early steel and wood window manufacturers began offering aluminum 

windows as an additional product line. 

Early aluminum windows can be generally characterized as either residential 

grade or commercial grade, with the 

latter designed particularly for larger 

window openings and non-residential 

applications. Early aluminum windows 

2 

Manufacturers either prescribed panning over all or part of the exposed 

steel components with aluminum or 

simply painting the steel and leaving 

it exposed. Although some residential grade windows came with similar 

steel components, most utilized an all 

aluminum sub-frame, sill, and mullion, 

often made with a thicker gauge of 

aluminum than the sash. 

Extruded aluminum was used to fabricate the frame and the sash. In crosssection, the aluminum frame for a hung 

window would usually consist of two 

or more extruded pieces, interlocked 

and secured with screws. Window 

sashes designed to look like wood 

double-hung or casement windows 

were often described as tubular or of 

hollow-metal construction by their 

early manufacturers. This distinction 

characterized the sash as a rectangular hollow construction, different 

from most steel window construction. 

Typically, the mitered corners of both 

the sash and aluminum frames were 

welded. Muntins were integral to the 

sash frame and duplicated the appearance of either wood muntins or steel 

glazing bars, depending upon the look 

of the window. 

Aluminum window sash tended to 

operate much in the same way as 

traditional wood or steel windows. For 

example, hung windows were set into 

either extruded channels similar to 

those used in some oftoday's aluminum windows or they were installed 

in guide strips similar to the stops and 

parting beads used in wood windows. 

Like steel windows of the time, many 

manufacturers of aluminum windows 

relied on the manner of construction 

and fit of operable units to minimize air 

Figure 2. Aluminum windows gained 

early attention in part due to their use in 

signature buildings and to their appeal to 

Art Deco designers. Still one of New York's 

finest Art Deco skyscrapers, the original 

Cities Services Building proj ected a strong 

corporate image and utilized aluminum 

in many f eatures, including the windows. 

(Photo: Shannon Koy.) 
infiltration and did not rely on weatherstripping. However, a number of early 

aluminum window companies did place 

considerable attention on well-designed 

weatherstripping features. Stainless 

steel or zinc weatherstripping was used 

along with wool felt, pile woven fabric, 

and other materials. Measures were 

also taken to reduce friction between 

the sash and frame, including the use 

of "bumpers" to cushion against jarring 

metal when operating the sash. Wool 

felt and rubber were used for ease of 

operation, along with newer synthetic 

materials such as Duprene, a rubberlike material manufactured by Dupont. 

Continuous fins or receptors for the 

weatherstripping and bumpers were 

often included as part of the extruded 

sections of the sash and frame. 

Hardware for aluminum windows drew 

heavily on that which was available 

for wood and steel windows. Spring 

balances and metal tape balances were 

popular for hung windows and placed 

in the frame, either at the head or jamb. 

For a sleek modern appearance, sash 

Figure 3. In 1938, the Flour City Ornamental Iron Company of Minneapolis was 

making aluminum double-hung windows. 

Instead of glazing compound along the 

glass edge of the sash frame, they extruded 

an aluminum bevel, a feature copied in 

many historic replications today. 

locks and lifts were available in white 

metal and chromed bronze to compliment the color of natural aluminum. 

Glazing depended on the type of 

window. Traditional outside putty 

glazing was common. Integral muntins 

were standard for divided lights. As 

with steel windows, some aluminum 

windows featured inside putty glazing, which was particularly desirable 

in factories. Some commercial grade 

windows with inside glazing included 

the option of using glazing beads for a 

more finished appearance. 

Various manufacturers also offered 

exterior insect screens with full-length 

tracks integral to the window frame. 

Others had full or half screens as separate attachments as well as full-length, 

removable, exterior aluminum storms. 

Early Finishes 

Aluminum windows came in a variety 

of surface treatments, including nonfinished, anodized, chemical conversion 

coatings, and painted (or lacquered). 

The most common finish used between 

1920 and 1950 was a "nonfinish," also 

called a "mill finish." These terms are 

used for a bare aluminum surface with 

only its natural oxide patina, which 

forms upon exposure to air. This natural film was thin, transparent, tough, 

and to a considerable extent, protective. Nonfinish aluminum varied in 

appearance, depending on the fabrication technique. The surface could be 

smooth, highly polished, or brushed. 

It could have a patterned texture as 

well, created by casting, extruding, or 

machining. With time, the unfinished 

surface darkened and discolored, eventually turning a darker color, typically 

gray. 

An anodized finish consisted of an 

extra thick coating of oxide film (from 

0.05 to over l.5 mils) produced in an 

acid bath by passing an electric current 

through the aluminum. The thickness 

of the coating was determined by the 

strength of the current and the duration 

ofthe treatment. The coating could be 

clear or integrally colored by adding 

pigments or dyes before it was sealed. 

Anodizing increased the resistance of 

the metal to corrosion and wear, and 

Figure 4. Early aluminum windows often 

mimicked wood windows in appearance 

and operations, even utilizing such details 

as parting beads, sash chains, and weights 

and pulleys. Photo of Folger Shakespeare 

Library in Washington, DC built in 1935. 

prepared the surface for other processes 

and coatings including paint. Although 

exceptionally resilient, anodized 

aluminum could still be damaged by 

harsh chemicals, abrasion, and abuse. 

Such conditions usually affected only 

the surface finish and did not reduce 

the service life of the aluminum. In the 

1930s and 1940s, this finish was used 

most extensively on naval aircraft, in 

particular on seaplanes, and was not 

readily available on architectural elements until the 1950s. 

A third type of finish was a chemical 

conversion coating which consisted of 

a thin oxide, phosphate, or chromate 

film formed by chemical reaction on 

the bare surfaces of aluminum and 

aluminum alloys. The coating could 

be dipped, sprayed, or brushed on, its 

thickness varying by the dwell time. 

This finish was thinner and less abrasion resistant than anodic coatings and 

was often used as shop preparation 

before painting. When a conversion 

coating was the final finish (without 

paint), it was typically clear or colored 

gold, gray, golden brown, green, or 

blue-green. 

3 
Whether clear (lacquer) or pigmented 

(paint), various types of organic coatings could be applied in the factory 

over a chemical conversion finish. 

In the field, a clear organic coating 

(lacquer) or a paint could be applied 

over a weathered or clean, grease-free 

surface, after the face had been mechanically or chemically roughened, or 

treated with a suitable wash primer. 

Causes of Deterioration and 

Common Problems 

Early aluminum windows were well 

constructed and, if properly maintained, were designed to last the life 

of the building. Some did incorporate 

features that proved deficient. As with 

the window industry as a whole, there 

were companies that provided low cost 

products with shorter service life or 

units not properly engineered for the 

size of the window opening. 

In assessing the condition of early 

aluminum windows, it is easiest to 

identify those problems that also are 

common with older steel and wood 

windows. At the same time, it is important to recognize areas of deterioration that are more specific to older 

aluminum windows. 

4 

Unless the windows have been regularly maintained, excessive air leakage 

may be a problem. It can be accompanied by water leakage as well. Leakage is commonly caused by cracked 

perimeter caulking, missing or cracked 

glazing putty, cracked or broken 

glass, and worn, ill-fitting, or missing 

hardware. Such conditions are typical 

of long-term use and deferred maintenance. If the windows originally 

incorporated weatherstripping, most 

of this material would have exceeded 

its life expectancy and would now be 

worn, cracked, deformed, or even missing altogether. 

Misaligned or deformed window 

sections can also cause air and water 

leakage. In investigating water 

infiltration around window openings, it is important to ascertain 

the actual source. Problems 

with the exterior wall rather 

than the window may manifest 

itself as moisture on the interior 

walls around window openings. 

Where windows have become 

misaligned over the years, it is 

common to find stopgap measures being used to reduce air 

Figure 5. During WWll, the federal 

government entered the aluminum 

business prodllcing large quantities 

for militmy applications including airplanes, gasoline tanks, artillelY shells, 

and canteens. This greatly diminished 

the availability of aluminum to the civilian bUilding industry and also fostered 

greater use of thinner gauge aluminum. 

By the 1950s, most aluminum windows, 

as in this 195/ apartment building in 

Washington, DC, were made lighter 

weight than their predecessors of the 

1930s, utilizing thinner gauge aluminum 

extrusions. 

aluminum subframes may prematurely 

corrode where in contact with damp, 

porous brickwork and stonework. It 

is thus important to insure that the 

connections ofthe subframe to the wall 

and to the window frame are secure. 

As with wood or steel windows, the 

most serious problems with the aluminum window frame and sash tend to 

occur where the units were originally 

undersized for the opening, have been 

subjected to intensive use and abuse or 

were of poor quality construction. Under such conditions, the windows may 

be racked or bowed and sections may 

even be bent or otherwise damaged. 

continued on page 8 

and water infiltration, such as 

retrofitted weatherstripping or 

caulk. Such measures often only 

aggravate the problem and lead to 

further misalignment. 

Moisture problems with the 

exterior wall also may affect the 

window subframe. Both steel and 

Figure 6. Deferred maintenance can result in a series of problems, such as broken hardware, cracked 

or missing glazing putty, and missing perimeter 

caulk (all shown above). All of these problems can 

be corrected. Note the uneven nature of the surface 

deposits of pollutants and grime on the mullion and 

sill of this window due to weathering and lack of 

cyclical cleaning. 
The U.S. Department 

of Justice Building, 

Washington, DC 

Located within the 70-acre 

Federal Triangle complex in 

Washington, DC, the U.S. 

Department of Justice Building is a monumental structure 

spanning an entire city block. 

Constructed of limestone, the 

seven-story building includes 

five separate courtyards of 

varying sizes. The large 

windows along the outside perimeter and in these courtyards 

provide natural light and ventilation to the offices as well 

as help define the architectural 

character of the building. 

Designed by the Philadelphia architectural firm Zantzinger, Borie and Medary, and completed in 1935, this 

classical revival style building reflected the architecture of 

existing buildings in the Federal Triangle complex. In a 

distinct departure, however, the extensive use of aluminum 

throughout the building, as both a utilitarian and a decorative metal, provided a showcase for federal architecture in 

the variable new uses of aluminum. Besides the 20-foot 

decorative entrance doors, aluminum was used for the interior stair railing, grills, doors, light fixtures, elevator cabs, 

and decorative artwork. In contrast to the steel windows 

commonly used in the federal complex, the 1,908 windows 

in the Justice Building were fabricated from aluminum. 

While it was $100,000 more expensive to use aluminum 

for features throughout the building, the architect justified 

the extra expense in terms of projected maintenance savings. 

Nearly 65 years after construction, the Justice Building underwent major renovation work, starting in 1999, to update 

systems original to the building. During the renovation, 

offices were relocated within the building to accommodate the work. The project included the restoration of the 

original 1 930s aluminum windows, which was undertaken 

in three phases and spanned a period of six years. 

The predominant window type consists of a pair of outward 

swinging casements centered above a hopper that opens 

inward. A single row of fixed lights flank the operable 

hopper and paired casement windows. Depending on the 

floor level and location, the individual windows had either 

a single or double row of fixed lights above the casement or 

none at all (Figure a). Windows with a single row of fixed 

lights at the top measured approximately 10'-2" by 5'-5" . 

Overall, the aluminum windows emulate the appearance 

Figure a. In the primary 

courtyard within the u.s. 

Department of Justice Building, the aluminum windows 

emulate the appearance 

of steel windows with tnle 

divided lights. Depending on 

thef/oor level and location, 

the windows differ in size and 

consist of a varying combination affixed lights, casements, 

and a hopper-style unit. 

of traditional steel windows and include true divided lights. 

The aluminum sash and frame have a mill finish that has 

weathered on the outside to a gray color. 

Window Survey 

A window survey was first undertaken to record the 

condition of each window and to inventory the hardware, 

fasteners, and missing frame pieces. Although the windows 

retained a high degree of historic integrity, some changes 

had been made over the years. To allow for the installation 

of ventilation louvers or window-mounted air conditioning units, over 400 of the hoppers below the casements had 

either been removed or had been rendered inoperable and 

the wide vertical muntin removed. Although the historic 

windows were not designed for weatherstripping, some of 

the windows had been retrofitted with weatherstripping to 

reduce air infiltration as a result of worn hardware or deflections in the operable units. At various times, caulk had been 

applied to set in replacement 

glass or to fill in unwanted 

gaps. Areas of surface deterioration were also evident 

including discoloration and 

varying degrees of corrosion 

and pitting. 

Figure b. The panes of glass 

were secured into the frame 

with aluminum glazing stops, 

each indiVidually cut, drilled, 

and fixed in place from the 

inside. Here the vertical stop is 

in place while the horizontal is 

missing. 

5 
6 

The renovation plan called for cleaning the aluminum 

window parts, replacing the existing glass and any missing or damaged parts, and making the historic windows 

fully operable again. Mock-ups of all phases ofthe work 

were required early on to establish the work standard to 

which the finished job would be held. It was anticipated 

that most ofthe work could be done in place, with work 

on the interior and exterior portions of each window done 

simultaneously. 

Abatement 

Early testing of the original glazing compound showed 

varying levels of asbestos. As a result, an abatement team 

was brought in to remove the metal glazing stops which 

secured the glass in place, dislodge and dispose of the 

glazing compound and existing glass, temporarily reinstall 

the glazing stops, and provide temporary protection over 

the unglazed window openings. Since each of the original metal glazing stops had been individually cut, drilled, 

and fixed in place when the glass was installed and were 

not interchangeable, it was important that each stop be 

returned to its original location. Thus, as each pane was 

abated, it was specified that the glass stops were to be put 

back in the same location and secured with mechanical 

fasteners (see Figure b). For the duration of the removal, 

6-8 crews worked at once. Each crew was to complete one 

window bay each day. 

Cleaning 

After the glass was removed, the aluminum frames and 

muntins were thoroughly cleaned on the inside with an 

aluminum jelly cleaner, pumice, and scouring pads, when 

needed. The aluminum was then rinsed to remove the 

cleaner residue (Figure c). For the exterior surfaces of 

windows that were more heavily corroded, the aluminum 

restoration company proposed a more aggressive chemical cleaner be used. This necessitated that the surrounding 

limestone surfaces around each window be well protected. 

During a mockup cleaning exercise, this chemical cleaner 

proved too acidic, difficult to control, and damaging to the 

adjacent stone. After testing some alternate products, the 

team found that a diamond abrasive pad used in combination with the Duro Aluminum Cleaner in jell fonn, worked 

the best. Special care was still necessary to protect the surrounding limestone. 

Some of the windows had areas of surface delamination. In 

such cases, the deteriorated surfaces were first ground down 

to remove the delamination and then cleaned as described 

earlier. 

Hardware 

The hardware used on the aluminum windows was similar 

or the same as used on comparable steel windows of the 

time. The hardware consisted of nickel bronze, brass, steel, 

or a combination thereof. Each of the individual casements 

was attached to the mullion with three hinges along the side. 

Fastened to each casement along the bottom rail and at the 

frame, casement adjusters pennitted each unit to be fixed in 

various open positions. To secure the casements closed, a 

cremorne bolt extended vertically at the intersection of the 

two casements. 

To permit the hopper to be opened inward for ventilation, it 

had a handle attached to the center of the top rail with a corresponding keeper at the frame, matching hinge 

arms that secured the side of each rail, and pivot 

hinges along either side at the bottom. 

Each piece of hardware was inspected for wear 

or damage. A number ofthe casement hinges 

were cracked or broken, which contributed to 

the malfunctioning of the operable sash. Deficient ones were replaced with new, matching 

hinges. 

Handles, adjusters, and cremorne bolts were 

cleaned, repaired, and lubricated as needed. 

Worn or redundant screw holes were filled in. 

Where hardware was missing or damaged beyond repair, original parts were salvaged from 

less significant areas, such as the basement and 

attic, for use on windows in more significant 

areas. 

Figure c. In cleaning historic aluminum windows, the gentlest means possible 

should be used. More aggressive cleaners should be used only where necessary. The interior sUiface of this window was cleaned tell years ago with all 

a/uminumjelly cleaner, rinsed and then dried thoroughly. The original mill 

.finish still retains its luster. 

It was also necessary to reproduce some of the 

missing hardware for use on the primary floor 

levels. For secondary locations, it was possible 
to purchase currently available new pieces that were similar but not exact matches. Some of the original hardware 

finishes were difficult to match but satin sanding and 

tumbling often brought the reproduction hardware closer 

to the historic appearance. 

It was decided early on that the mechanical fasteners, 

which included primarily aluminum but also some brass 

screws, would largely be replaced because of their age 

and condition. Some were unique in size and shape, and 

had to be specially made. 

Extrusions 

Sections of the window frames had been removed or 

cut away to allow for various alterations over time, including the installation of window air conditioner units 

and ventilation louvers. Some original pieces were 

found in the attic of the building and were subsequently 

reused. 

An aluminum company reproduced the vertical muntin 

that historically existed in the hopper unit but was missing from numerous units. After the muntins were cut to 

size, each was slotted at the end and fitted into the hopper 

frame, and then welded at the tip. The same company 

also made custom extrusions for the rails and stiles of the 

hopper units for use in fabricating entire hoppers where 

missing (Figure d). 

Additional Repairs 

Most of the repair work was done on site. Units that 

needed to be completely reconstructed (Jess than 5%) 

were moved to a welders shop. Where areas of severe 

corrosion on the exterior of the windows were encountered, Lab-Metal, a high temperature repair epoxy, was 

used to fill voids and to build-up surfaces to their original 

outside dimensions. Because the windows were generally in good condition, the use of epoxy fillers was not 

widespread. 

In very limited areas on the exterior where severe delamination had occurred, the flaking aluminum was removed, 

epoxy applied to even the surface, and then an aluminum 

flat bar was attached with stainless steel screws to reestablish the original profile. 

Replacement Glass 

After the windows had been cleaned and repaired, new 

glass was installed from the inside. Unlike the original 

glass, 6.4 mm laminated glass was used as a replacement, 

providing the additional qualities of shatter resistance and 

enhanced energy performance. The laminated glass consisted of an outer layer of clear, heat-strengthened glass 

Figure d. Numerous hopper units have been removed over time to 

accommodate air conditioning units. Replacement hopper units 

were manufactured, as needed, to match the original hoppers 

elsewhere in the building. 

with a Low-E coating and an inner layer offully tempered 

glass. A contemporary glazing tape was used instead of 

glazing compound to seal the glass and the aluminum 

glazing beads were affixed to the inside with screws to 

secure the glass. It was necessary to purchase additional 

aluminum glazing bead to augment historic beads that 

could not be reused. 

PROJECT DATA 

Owner: 

General Services Administration 

Project Manager: 

Gilbane Building Company, Washington, DC 

Window Contractor: 

Clyde McHenry, Inc., Hyattsville, MD 

Aluminum Cleaning and Finishing: 

Atlantic Refinishing & Restoration, Inc., Waldorf, MD 

Hardware Supplier: 

Blaine Hardware Inc., Hagerstown, MD 

Glass Supplier: 

Northwestern Industries, Inc., Seattle, WA 

Project Date: 

1999-2005 

7 
Factory windows and residential windows of very lightweight construction 

were most prone to such problems. On 

many buildings, however, such conditions are uncommon or are limited to 

only some windows. 

More common are instances where 

sash have been damaged as a result of 

previous retrofits of either mechanical vents or window air conditioning 

units. Such installations may also have 

resulted in the removal of one or more 

muntins to accommodate these units. 

While interlocking seams were found 

on some early aluminum windows, 

units were normally assembled using mechanical fasteners and welded 

joints. Operable units that were 

primarily welded together tend to have 

been higher quality windows and are 

generally fo und in better condition than 

windows that were mostly fastened 

together with screws, bolts, or rivets. 

Machine screws may have a tendency 

to loosen over time, which can contribute to various problems that require 

remedial work. 

In assessing the condition of the sash 

and frame, any flanges and receptors 

for weatherstripping that were extruded 

as part of the sash or frame should 

be examined, as some sections may 

have been damaged over time. Aluminum glides or stops for operable sash 

also need to be checked to detemline 

whether they are bent, gouged, corroded, or painted. These conditions 

could impede the ease of operation of 

the sash. 

Other problems that can affect the 

operability of the window include 

broken balances, corroded and broken 

hardware, misaligned or loose hardware, and windows that have been later 

sealed or painted shut. 

While aluminum is resistant to most 

types of corrosion, it is affected by 

certain agents such as alkalis, hydroch loric acid, and lead-based paints. 

While considered a durable building 

material, aluminum does deteriorate. 

It is subject to corrosion when wet and 

in contact with certain alkalines, such 

continued on page 11 

8 

The Raymond M. Hilliard Center 

Chicago, Illinois 

Built in 1966 by the Chicago Housing 

Authority, the Raymond M. Hilliard 

Center was originally a public housing complex offive buildings with 7\0 

apartments located south of Chicago's 

downtown loop. Designed by Bertrand 

Goldberg, it is acclaimed for both its 

mixture of elderly and fami ly housing 

and its modern "new-expressionist" 

architecture. Of special note are the 

2,300 window openings of a modified ellipse shape with the bottom and 

top curved segments compressed into 

straight parallel edges, set into the 

concrete walls of the tower buildings. 

These openings have been described 

as "television sets," "beehives," and 

"airplane windows" (Figure b). The 

windows are a combination of two 

rectangular aluminum horizontal slider 

sash with flanking radial fixed panes. 

Each flanker is set back at an approximate 22.5-degree angle to the outer 

face of the center units, conforming to 

the curved outer wall (Figure a). 

SLIDER 

UNIT 

Problem 

Figure a. One of two 

identical 16-s1OIY senior citizen apartment 

buildings within the 

Raymond M. Hilliard 

Centel; each with /82 

apartment units. The 

window openings are 

elliptical in shape and 

center on each reeded 

bay. (Photo: Holsten 

Real Estate Development Corp.) 

Early on, the private developer, Holsten Real Estate Development Corporation, committed to rehabilitating the 

Hilliard Center for continued use as 

mixed-income housing. They recognized the importance of the original 

aluminum windows and sought to 

preserve as many as possible. Distinctive in their configuration and form, 

the windows, however, were light 

residential units manufactured with 

atTordability in mind. They had thin 

aluminum members, lacked drip edge 

or weeps to direct water away from 

the openings, and, typical of the time, 

were only single glazed. There were 

provisions for insect screens but not for 

storm windows. 

Nearly all of the original windows had 

survived 40 years of Chicago's harsh 

winters and numerous abuses from 

high-density occupation. The architect 

completed a condition survey of 120 typical windows 

and found that 61 % of the 

windows lacked the original 

glazing (replaced with 

CAST 

IN 

PLACE 

CURVED 

CONC 

'MNDOW 

OPENING -+\--t-- FIXED Plexiglas or similar material), 31 % had damaged 

operating sash, 29% were 

£Won 

3 EXISTING WINDOW ELEVATION 

Figure b 

SIDE 

LITE 

boarded up with damage to 

the frame, 25% were missing their original operating 

glazing sash, and 71 % were 

missing screens. Only 15% 

of the windows had no visible defects. 
Solution 

The decision was made to save the 

historic windows for the first four 

floors of the towers, since they would 

be most visible from the ground. Units 

on the first four floors in bad condition 

were to be replaced by windows in 

better condition relocated from above 

floors. Matching aluminum replacement windows were to be installed on 

the upper floors. 

The window survey provided an overall view of the necessary repair work to 

the historic units. There were standard 

components within each of the different window types and the aluminum 

had proved durable where not abused. 

Thus it would not be necessary to replace large numbers of the entire window assembly within each bay on the 

lower floors. The windows could be 

repaired, utilizing parts easily salvaged 

from other units within a building to 

replace worn-out or missing ones. In 

the total project, 336 original windows 

were to be repaired and 2,016 to be 

replaced. 

SLIDING 

WINDOW 

MEETING 

RAIL 

Figure c. Detail showing the sliding aluminum meeting rails in a closed position. 

(Drawing: Holsten Real Estate Development Corp.) 

Disassembly and Salvage 

Windows on the upper floors that were 

in good condition were marked for 

salvage and then taken to the repair 

shop in the basement. There they were 

sorted and stacked by size and by their 

original inside or outside position in 

the window track. 

ALUMINUM 

SUDINC 

WINDOW 

UNIT 

Figure d. Both the interior and exterior faces 

of the window are set back on a slight reveal in 

the wall. The curved portions of the windows 

are fixed while the central rectangular section 

is fitted with sliding sash. Rivets secured the 

flankers to the window assembly. (Drawing: 

Holsten Real Estate Development Corp.) 

For the window repair work on the 

lower four stories, a portable shop 

area was created on each floor. Here 

the crew assembled a gang box of 

their tools to be used: 6" metal bender, 

reciprocating saw, chisels, screw 

drivers, scrapers, wire brushes, drills, 

acetylene torches, caulk, and caulking 

guns. 

Most of the frames could be repaired 

in place. In areas where the frames 

were to be removed and replaced, 

a reciprocating saw was used to cut 

the rivets holding them in place. A 

1/8" space adjacent to the frame was 

needed to accommodate the blade to 

cut the rivets. When the frame was 

too tight against the concrete, a 6" 

bender was used. This work was done 

from the inside of the window both 

for convenience and also not to damage the exterior finish of the unit. The 

mastic that held the window frame 

to the continuous aluminum closure 

piece was also cut away. Once loose, 

the frames could be grabbed on both 

ends and lifted out of the opening. 

One of the more time consuming aspects of the project involved the radial 

flankers. Many of these historic window units were broken and had been 

caulked together in a repair effort. 

Due to age and stiffness, it was necessary to first heat the sealing gasket for 

RIVET 

WiNDOW 

WORK 

POINT 

CAST IN PLACE -I------~ 

ALUMINUM 

INSERT 

the glass with a small acetylene torch. 

The gasket could then be removed 

from around the frame. thus freeing 

the broken glass for disposal. Typically this involved the handling of a 

number of broken pieces of glass and 

subsequently took a great deal of time 

to clean it down to the raw opening. 

If the frame for the flanker unit was to 

be removed, rivets securing the unit 

were cut at both ends and the unit lifted out (Figure d). At this point, the 

only remaining window piece in the 

opening was the aluminum subframe 

to which the window frame was attached. Set within the concrete walls, 

the subframe was left undisturbed. 

Salvaging parts from upper level 

windows saved considerable money. 

This was particularly the case where 

entire operable units were taken intact 

and reused from upper floor units. As 

a result of salvaging parts, no new 

parts were needed other than items 

such as rivets and weatherstripping. 

Even latch mechanisms and locks 

were salvaged by first removing the 

old rivets and then cleaning and reattaching them as needed. 

Cleaning Procedure 

Over the years many attempts had 

been made to make the windows 

9 
10 

operate better. As units became worn, 

loose, or deflected, pieces of weatherstripping were added between the sash 

and sash tracks to better seal out the 

cold. Metal plates were added to the 

bottom of the operable sash to enable it 

to better slide in the channel and caulk 

was applied to close up unwanted openings between the glass and the frame, as 

well as to repair broken pieces of glass. 

Residual dirt, putty, grease, and paint 

coated many of the window units. 

The aluminum surfaces needed to be 

cleaned and taken back closer to their 

original appearance. Because of the 

effect of weathering and use, it was 

considered acceptable in this project 

to use certain cleaning techniques 

not nonnally recommended for more 

ornamental architectural aluminum. 

A common chemical cleaner and/or 

Figure e. Both interior and exterior 

aluminum suifaces 

had become dull, 

soiled. and oxidized 

as a result of traffic 

exhaust and air 

pollution. Cleaning the aluminum 

stabilized any further deterioration 

and brought back 

the luster of the 

original mill finish. 

(Photo: Holsten 

Real Estate Development COtp') 

denatured alcohol were used to 

remove the general residue on the 

aluminum. Wearing rubber gloves, 

the crew wiped on the cleaner with a 

damp cloth, allowed it to stand for 3-

5 minutes, and then wiped it off with 

a clean damp cloth. Scouring pads 

and scrapers were sometimes used on 

more encrusted areas, as needed. The 

removable sash lmits were cleaned in 

the basement shop, while any frames 

that remained in situ were cleaned in 

place (Figure e). 

Repair and Reinstallation 

Some window units were in such 

good condition that they only needed 

to be cleaned, with any minor repairs 

being made at the same time. Others 

required more substantial work and 

were sent to a separate workstation after cleaning. 

Repairs varied from 

replacing or resecuring any loose screws 

holding the sash frame 

together, to realigning 

pieces by bending or 

refonning. All the sash 

hardware was cleaned, 

lubricated, and then 

reattached. 

Figure f Repair and replacement work was done from the 

inside to lessen the risk of damage to the outsidefinish. 

(Photo: Holsten Real Estate Development Corp.) 

There were a sufficient 

number of operable 

sash with existing 

glazing and frames in 

serviceable condition 

that they could be used for the entire 

lower four floors. Such was not the 

case with the flankers where 50 pieces 

of glass costing a total of $1,300 had 

to be ordered to augment what existed. 

Before the new glass for the flankers 

could be installed, a template in the 

shape of the radial opening was made 

and then taken around to various openings where glass was to be replaced. 

Adjustments to the shape were made as 

needed in an effort to get the best-standardized shape. The new glass was 

custom ordered and delivered to the 

on-site shop for installation. 

When reinstalling window units, care 

was taken to ensure correct alignment. 

This was partic.ularly important with 

the operable units to guarantee a good 

weather tight seal when closed (Figure 

f). New screen windows were installed 

as part of the final completion work. 

PROJECT DATA 

Owner: 

Holsten Real Estate Development 

Corporation, Chicago, IL 

Project Date: 

2001-2004 

Architect: 

Lisec & Biederman, Ltd., Architects 

and Planners, Chicago, IL 

General Contractor: 

Linn-Mathes Inc., Chicago, IL 

Glass Contractor: 

Tortensen Glass, Chicago, IL 

Window Screen Supplier: 

Commons Manufacturing, Chicago, IL 

Project cost: 

The cost for window repair, including 

both labor and materials, totaled $1,486 

per window. The cost for a new aluminum unit ran $1,700 per window. 
7 

Figures 7 and 8. Aluminum corrosion can appear as a white discoloration andforms on the surface as the protective oxide film breaks down, as 

seen in these 60 year old windows in the PSFS Building, Philadelphia, before they were replaced. The small dark bumps are where surface dirt, 

grime, and pollution particles collect. Over time, pits form beneath these dark areas as the surface continues to corrode. This corrosive action 

is filrther encouraged by foreign particles, such as dirt and chlorides, which hold moisture next to the surface. (Photo: Powers & Company Inc.) 

Figure 9. Some aluminum alloys are less corrosion resistant than others. Delamination, as seen on this aluminum railing in front of a window at 

the Folger Shakespeare Library, can occur when an aluminum-copper alloy is introduced and used in an outdoor setting. The original specifications called for aluminum and chromium, but were not followed. 

as concrete, mortar, and plaster. Some 

forms of wood, wallboard, lead-based 

paints, and insulation materials may 

also attack aluminum. Particularly 

important, acid-based chemicals used 

to clean masonry surfaces can also corrode aluminum. 

Aluminum is also subject to damage by 

galvanic action when in contact with 

certain dissimilar metals such as copper and steel. Nonconductive materials like paint or mastics are needed to 

electrolytically insulate the metal. This 

was a common procedure where steel 

was used as the subframe for aluminum windows. 

Aluminum and any protective 

oxide films and finishes are also 

subject to deterioration caused 

by air-borne abrasives. Certain 

air pollutants, dirt, sand, and high 

humidity work to break down the 

protective finishes. When combined with a low priority maintenance program, they will shorten 

the life span of an aluminum 

window. 

Understanding the variety of aluminum alloys, tempers, finishes, 

and treatments used historically 

tion finishes. Simple tests using a steel 

needle or a rubber eraser in a small 

area can preliminarily identify finishes. 

Laboratory analysis can also be used to 

confirm alloys, tempers, and coatings 

but often require the removal of window sections and destructive testing. 

Cleaning 

Aluminum windows can benefit from 

periodic cleanings. Even a simple 

water wash can cut down on the accumulation of surface dirt and pollutants. 

A mild soap and water may be safely 

applied to any aluminum finish. 

The effect of different chemical cleaners on aluminum depend on many factors, including chemical concentration, 

dwell time, and temperature, as well as 

the aluminum alloy type, production 

method, surface finish, and coating. 

The Care of Aluminum, a technical 

guide published by The Aluminum 

Association, provides useful information on the maintenance of aluminum, 

including the cleaning of surfaces and 

is important to uncovering the 

specific causes of deterioration and 

to developing sound conservation 

approaches. Visual examination can 

help determine or confirm producFigure 10. The shine and luster of an aluminum window with an original mill finish was a perfect compliment to the stainless steel exteriors found on 1940s11950s diners. The Hollywood Diner is an authentic Mountain View Diner built in 1954. Itfirst operated in Westbury, New York and was later moved to 

Baltimore, Maryland. In the 1980s it was the location site for several Barry Levinson'sfilms including 

"Diner." Most of the original windows remain in this building. 

11 
Figure 11. Aluminum windows were described as a perfrect choice for Lustron Homes because 

of their modern appearance and ease of maintenance. Along with the procelain-enameled-steel 

exterior wall panels, the manufacturer claimed that the only cleaning and maintenace materials requiredfor a Lustron Home were "soap, water, and a damp cloth." Today, cleaning is 

recommendedfor any historic aluminum window as part of a cyclical maintenance program. 

application of watertight protective 

coatings. 

The Association 's technical guide lists 

five categories of aluminum cleaners: 

I) mild soaps and detergents, and nonetching cleaners, 2) solvent and emulsion cleaners, 3) abrasive cleaners, 4) 

etching cleaners, and 5) special heavyduty cleaners. In dealing with historic 

materials, the gentlest means possible 

should be used to clean aluminum 

windows. More aggressive cleaners 

should be used only where necessary. 

The goal of cleaning is not to return the 

aluminum to an "as good as new" look, 

but rather to remove harmful deposits 

and, where appropriate, improve the 

existing appearance where corrosion or 

deposits have significantly altered the 

historic appearance. 

In many cases of deferred maintenance, 

abrasive cleaning methods appropriate for aluminum will be needed to 

remove surface oxidation and heavy 

encrustation. These cleaners come in 

different forms, such as polishes, metal 

brighteners, and powders. Only certain 

mild abrasives should be considered for 

anodized, painted, or chemical conversion coatings to avoid damage to the 

finish. With nonfinish aluminum, abrasive cleaners may be used in combination 

with fine stainless steel wool or abrasive 

nylon pads, depending upon the need and 

the results of cleaning tests. Alternatively, etching cleaning may be used instead 

on nonfinish aluminum, again depending 

upon test results. When other means are 

unsuccessful on nonfinish aluminum, medium abrasive cleaners or mechanically driven pads of fine steel wool 

or abrasive nylon can be considered 

in limited cases. Special care must 

be taken to protect the glass. These 

more aggressive cleaners and 

methods should not be used simply 

for expediency when more gentle 

abrasive cleaners are also effective. 

Figure 12. Cleaning tests may include 

a variety of products and methods such 

as mild soaps and detergents, etching 

cleaners, and abrasives. The gentlest means possible should be used, 

understanding that the goal is not to 

create a like-new appearance but rather 

to remove excessive grime and surface 

pollutants. Use of heavy etching cleaners or heavy-duty abrasives should be 

avoided on certain historic finishes. In 

this photographs a mild etching cleaner 

injellform is being tested on a storm 

window with a millfinish. 

Spot tests should always be performed 

beforehand to determine the suitability 

of any application to an existing finish. 

Regardless of the type and strength 

of any required cleaner or its form 

of application, it is important that all 

cleaned surfaces be thoroughly rinsed 

and wiped dry. 

A cyclical program of cleaning using 

a gentle method will help maintain a 

newly cleaned finish. Clear lacquers 

or waxes can be applied to nonfinish, anodized, and conversion-coated 

aluminum to help protect the newly 

cleaned finish as well. A clear lacquer 

application (sprayed or wiped on) will 

preserve the appearance of cleaned 

aluminum for an appreciable time. 

Wax offers a shorter protective life and 

will require frequent reapplication. In 

cases where the anodized finishes have 

failed and cannot be restored through 

cleaning techniques, painting may be a 

suitable option. 

Common Repairs 

Early residential and commercial grade 

aluminum windows share various 

common maintenance approaches and 

repair techniques. However, repair 

approaches must be tailored to the 

specific project. For example, when 

working with early heavy-gauge 

aluminum windows that emulated steel 

12 
Figure 13. As early as the 1930s, companies primarily making aluminum windows often offered an option for an aluminum storm windo"vl, 

usually on the exterior. The left-hand photograph shows an early interior storm window piggybacked onto the primmy window frame at the 

Folger Shakespeare Library (glass pane on the left). The photograph of the same window, fi-om the outside, shows no indication of an interior 

storm. 

window design and construction, many 

of the common repair procedures for 

steel windows can apply. However, it 

is important to take into account that 

aluminum is a much softer material 

and greater care must be taken to avoid 

surface damage. 

As with any old window, certain precautions should be taken before undertaking repair work. While aluminum 

windows generally were designed not 

to be painted over time, lead paint may 

have been used in subsequent years to 

refresh the appearance, particularly on 

the inside. Tests for the presence of 

lead paint and also for asbestos in the 

glazing compound should be undertaken and any remedial work completed as 

required. 

For windows that have not been regularly maintained, any original weatherstripping, if present, will probably 

need to be replaced. The options for 

installing replacement weatherstripping 

depend partly on how the window was 

originally weatherstripped. It could 

have been set in channels or grooves or 

more simply surface applied. Whether 

to use traditional weatherstripping or 

contemporary synthetic products is 

a decision that can only be made by 

understanding how the weatherstripping was integrated into the existing 

window and what materials are available today. Because of peculiarities 

of some early aluminum windows, it 

may be necessary to explore potential 

sources of weatherstripping not normally considered for windows, such as 

from the broader building industry or 

transportation field. 

Where weatherstripping was not an 

integral part of the original window, 

caution should be taken not to install 

weatherstripping in a manner that will 

stress either the hardware or the window over time. Like most traditional 

steel windows, good quality, historic 

aluminum windows relied on tight 

alignments and proper fitting of operable parts to minimize air infiltration. 

When repaired and properly aligned, 

it may not be possible or necessary 

to retrofit weatherstripping. In most 

cases, weatherstripping should not be 

used to close gaps attributed to distortions around the operable window, as 

this will only exacerbate the problem. 

Rather the distortions or misalignments 

in the sash or frame should be corrected. New weatherstripping should 

be installed in a manner that is easily 

reversible, considering that the material 

will in the future need to be replaced. 

It is common to find that the glazing 

putty is cracked, loose, disintegrating, 

or largely missing. This is primarily 

attributed to the age of the material 

and subsequent lack of proper maintenance. The old putty will need to 

be cleaned out, taking care to protect 

any glass that is to be reused. This is 

particularly important with old wire 

glass and certain patterned glass that is 

not available today. Where windows 

are inside glazed using aluminum beads, 

care should be taken in removing the 

beads, when in good condition, so that 

they can be reused. Since glazing beads 

may not be interchangeable even within 

a single window, it is important to mark 

each piece for reattachment in its originallocation. When reglazing, a glazing 

compound suitable for metal should be 

used. Glazing tape and other contemporary glazing products can be used as 

appropriate, provided the appearance of 

the glazed lights is not changed. 

Some early aluminum windows were 

designed to accommodate either single 

or dual glazing (see Figure 10). With 

some heavy gauge aluminum windows, 

it may be possible to retrofit insulating 

glass even where dual glazing was not 

an original option. For enhanced energy 

performance, an alternate approach 

that is more commonly used involves 

replacing the existing glass with new 

laminated glass that includes a Low-E 

coating or film for enhanced energy 

performance. 

It is important to inspect the mechanical fasteners that secure the frame to 

the opening and any that were used to 

assemble the window. Loose fasteners 

13 
will need to be tightened and deficient 

ones replaced with screws appropriate 

for use with aluminum. Welded joints 

that have failed should be re-welded 

and any cracks in the frame repaired. 

Missing or 

Damaged Sections 

Techniques for repairing missing 

or damaged sections of aluminum 

windows vary according to the type 

and quality of the historic units. One 

approach is to cannibalize units that 

will be replaced. Damaged pieces of 

the frame, sash, or sill can be detached 

by removing fasteners or cut out. 

Salvaged pieces can then be reattached 

with traditional fasteners, welded in 

place, or secured with contemporary 

bonding material. Filler material, especially made for aluminum, can be used 

to fill holes and, depending upon the 

makeup of the window, to fill depressions caused by abuse or delamination. 

For larger projects involving common missing sections, such as muntins 

that have been cut out for window air 

conditioning units, a custom extrusion 

can be made to match the shape and 

profile of the missing pieces. These 

pieces can then be cut and welded in 

place. Entire units can be replicated 

where sufficient quantities merit the expense of such custom work. For small 

projects, it may be possible to have a 

machine shop mill the missing pieces 

from standard aluminum stock. 

Hardware 

A wide variety of hardware is found on 

older aluminum windows, including 

locking handles, lifts, balances, sash 

chains, hinges, fasteners, and casement 

operators. Most existing hardware 

will need to be cleaned and lubricated. 

In many cases, this requires removing the hardware to do the work and 

reattaching each piece in its original 

location, after the work has been done. 

When present, worn sash chains can be 

replaced with new ones that match the 

original ones. 

Figure 14. Hardwarefor early aluminum 

windows came in a variety of materials including steel, bronze, and nickle. Specialty 

hardware manufacturers can easily replicate suitable replacements today, matching 

the originals in both material andjinish. 

The manufacturer's stamp, visible through 

the glass on the exterior sill of this window 

at the Folger Shakespeare Library in 

Washington DC, identifies Wm. H. Jackson 

Company of New York as the maker and 

dates the window patent to 1926. 

For severely worn, broken, or missing 

hardware, several options exist. Specialty hardware companies may stock 

matching replacement or reproduction 

pieces. Original hardware can be duplicated or suitable replacements may 

be available from salvage companies. 

Similar hardware can be used where 

functional rather than visual match suffices. Alternatively, original window 

hardware can be taken from secondary 

locations within a building for use in 

more prominent areas, and stock new 

hardware used as a substitute in the 

secondary locations. 

When retrofitting existing aluminium 

frames with insulating glass, special 

care should be taken to insure that 

older hardware can handle the added 

weight. 

This Preservation Tech Note was prepared by the National Park Service. Charles E. Fisher, Technical Preservation Services, is the 

Technical Editor of the Preservation Tech Notes series. Infonnation about the U.S. Justice Building was generously provided by 

Clyde McHenry of Clyde McHenry, Inc., and Cathy McIntyre and Mike Ragan of the U.S. Department of Justice. Information on 

the Raymond M. Hilliard Center was generously supplied by Peter Holsten and Andy Hestness of the Holsten Real Estate Development Corporation. Thanks are also extended to Charles Fisher and Rebecca Shiffer of the National Park Service for their review and 

assistance. Thanks also go to The Aluminum Association; Edward Bartlett, Custom Window Company; Sam Wharton, Fenestra, 

Inc.; and Alex Paolucci, Atlantic Refinishing & Restoration Inc., for their assistance. Unless otherwise noted, photographs are by 

the author. 

Preservation Tech Notes are designed to provide practical information on traditional and innovative techniques for successfully 

maintaining and preserving cultural resources. All techniques and practices described herein conform to established National Park 

Service policies, procedures and standards. This Tech Note was prepared pursuant to the National Historic Preservation Act, which 

directs the Secretary of the Interior to develop and make available to government agencies and individuals information concerning 

professional methods and techniques for the preservation of historic properties. 

Comments on the usefulness of this inforn1ation are welcomed and should be addressed to Preservation Tech Notes, Technical Preservation Services, National Park Service, 1849 C Street NW, Washington, DC 20240. 

ISSN: 0741-9023 PTN-5l May 2008