Prepainted
Galvalume Sheet -
A Superior Material for Architectural Roof and Wall
Systems
Prepainted
Galvalume� sheet is ideal for a wide range of painted
applications.
Especially when
superior atmospheric corrosion resistance is required in
pre-engineered buildings, architectural panels, siding,
roofing (both conventional and standing seam) and many
other building components.
In addition, this
highly cost-effective product offers designers and users
alike a wide variety of color options, design
flexibility, long-term durability and ease of
installation.
What's more, all
prepainted Galvalume sheet products blend harmoniously
with virtually all other building materials.
Galvalume is a
registered trademark of BIEC International, Inc.
The metallic
coated steel substrate
The trade name,
Galvalume, is used to identify cold-rolled steel sheet
products to which a corrosion-resistant aluminum-zinc
alloy coating has been applied. It is produced by a
process developed by Bethlehem. The Galvalume sheet
coating consists of an alloy of 55% aluminum, 43.4% zinc
and 1.6% silicon, nominal percentages by weight, as
listed in ASTM Designation A792. On a volume basis, the
coating is approximately 80% aluminum. The metallic
coating is applied by a continuous coating process
whereby properly cleaned low-carbon, cold-rolled sheet
steel is dipped into a molten aluminum-zinc bath. The
result is a highly corrosion-resistant sheet steel that
delivers the best protective features characteristic of
aluminum and zinc: the barrier protection and long life
of aluminum plus the sacrificial or galvanic protection
of zinc at cut or sheared edges. More than two decades of
actual outdoor exposure have demonstrated that Galvalume
sheet exhibits this excellent combination of properties.
Premium-quality
paint systems
A broad range of
paint systems can be applied to this highly
corrosion-resistant base to enhance durability, add color
and beauty, and provide creative options for design
professionals. Bethlehem's well-regarded reputation for
premium quality is maintained throughout. Bethlehem has
instituted a process control program to insure that
prepainted Galvalume sheet is produced to prescribed
standards. The program specifies the methods and
materials to be used in each phase of the painting
process. Stringent product performance requirements are
specified, as well.
Chromate
pretreatment: The chromate pretreatment provides a
superior combination of flexibility and corrosion
resistance compared to other types of pretreatments, like
zinc phosphate or complex oxide typically used for
prepainted galvanized sheet. Pretreatment coating weights
are monitored using X-ray fluorescence measurements to
assure optimum quality.
High-performance
primers: Rigorous laboratory and atmospheric exposure
tests are conducted to insure that primers used on
prepainted Galvalume sheet will provide excellent
sheared-edge corrosion resistance and paint adhesion in
addition to superior long-term performance at flat,
formed, and paint-damaged areas. With the use of these
Bethlehem-approved primers, edge creep performance along
sheared edges of prepainted Galvalume sheet is comparable
to that exhibited by conventional prepainted galvanized
sheet.
Approved paint
systems: Many paint systems have successfully passed
Bethlehem's performance requirements and earned their
place on the "Approved List." New systems are
continually being evaluated to provide the widest choice
of advanced paint technologies. Paint suppliers who have
developed these high-performance systems include Akzo,
Dexter, Glidden, Morton, PPG, Sherwin Williams and
Valspar.
Long-lasting beauty
and durability: Prepainted Galvalume sheet from
Bethlehem, processed according to stringent
specifications, is far ahead of competitive materials for
architectural applications. Tough laboratory and
atmospheric evaluations attest to prepainted Galvalume
sheetls excellent long-term performance. With the
availability of polyesters, silicone polyesters,
fluorocarbons and plastisols, there is a paint system to
match your performance and budget needs.
An ideal material
for the 90s and beyond
Metal building
systems and components play a major role in contemporary
architectural design. Today, bare and prepainted metals,
such as Galvalume sheet, are widely used as finish
materials -- both internally and externally, for new
construction, as well as for rehabilitation. Prepainted
Galvalume sheet's flexibility and versatility respond
well to the interest among architects in the generous use
of color and in the diversity of formal architectural
expression.
Long-term
durability: The outdoor atmosphere has become
increasingly corrosive, placing unprecedented demands on
long-term durability and corrosion resistance on all
exterior building materials. Today's treatments and
coatings, such as those specified by Bethlehem, ensure
that building exteriors will remain highly resistant to
both man-made and naturally-occurring hostile
environments.
Technical
flexibility: Galvalume sheet panels can be combined with
a variety of specialized treatments and with other
materials to meet a variety of project-specific needs.
For example, fire-resistant construction and thermal
insulation properties can be incorporated into the panels
without affecting their exterior appearance. This
enhances the potential for continuity in the outward
appearance of a design, while the unseen treatments and
technical properties are able to respond to special
project requirements.
A cost-effective
material: Metal systems and components, fabricated of
Galvalume sheet, are competitive with the installed costs
of other cladding approaches. Galvalume sheet provides
significant life-cycle cost advantages due to its
durability and low-maintenance requirements. The use of
factory-applied treatments, coatings, and paints results
in cost and performance advantages over field-applied
treatments and finishes.
Rapid installation:
Building systems and components fabricated of Galvalume
sheet can be erected quickly and easily. No extra on-site
treatment or additional finishing is required. Projects
can be enclosed and protected from the weather more
quickly. And installation is not hampered by adverse
weather or by other variable environmental conditions.
Easy to ship and
store: Galvalume sheet components are lightweight and
easy to nest or stack, reducing shipping costs and
requirements for jobsite storage and lifting.
Adaptability and
compatibility: Prepainted Galvalume sheet metal
components combine well with most other building
materials and treatments, and can be adapted to work in
concert with almost any design approach. Treatments and
effects that are standard for metal components would be
difficult or impossible to attempt with other materials
and techniques. Prepainted Galvalume sheet's versatility
allows it to be used almost anywhere on building
interiors and exteriors, assuring compatibility and
simplicity in the overall design approach.
Flexibility in
texture and pattern: A wide variety of seams, joints,
ribs, fastening devices and surface treatments is
possible, enabling designers to develop almost any
desired effect. Prepainted Galvalume sheet in building
systems and components can be designed to match or
coordinate with textures and patterns produced by many
other building and cladding materials, including exposed
concrete, wood and glass curtain-wall systems.
High
strength-to-weight ratio: Building systems and components
fabricated of Galvalume sheet are strong and light in
weight permitting their use for special effects not
possible with other materials. Their light weight means
less structural deadloading and greater freedom in the
use of slender architectural elements.
Color, color,
color: Today's paint system suppliers offer a wide
variety of color and finish options. Thus, the
imagination of the design professional remains
unrestricted in the use of color to develop full
architectural expression.
Unlimited
applications
Roofs, fasciae and
soffits: The superior appearance and performance of
today's standing seam metal roof -- now more widely
specified than any other metal roof type -- has resulted
in a resurgence of interest among architects and owners
to make the roof visible. Roofs have become part of the
architecture and are no longer just an element to keep
out water. Metal roofing systems, produced from
prepainted Galvalume sheet, offer great potential for the
use of roof colors that complement the color of the other
architectural elements. A wide variety of roof panel
widths and seam effects can be achieved. Both high-and
low-standing seams are available.
Designers should
become familiar with and work within the modular
dimensions of the particular standing seam roof system
being specified. Through-roof penetrations for skylights,
hatches and other features should be laid out to fall
between -- not directly on -- seams. Overall building
geometry and dimensions should relate to the pattern and
interval of roof seams.
Claddings, sidings
and spandrels: For curtain-wall, cladding and siding
applications, large facade areas can be covered with the
confidence that panel appearances and desired
architectural effects will be uniform over the entire
area of application. Because the quality of
factory-controlled paint applications cannot be matched
in the field, the use of prepainted Galvalume sheet
panels helps to assure that color rendition and panel
appearance will be uniform throughout the project.
Flexibility in
color choice also provides greater opportunity for the
selective use of metal on facades, in combination with
masonry, concrete, wood and other materials. For projects
that combine other exterior finishes and materials with
metal, the availability of such materials as prepainted
Galvalume sheet minimizes difficulty in matching or
complementing desired colors.
Mansards and
canopies: Many architectural exterior building elements
can be designed and produced from the same prepainted
Galvalume sheet steel used for the building roof and
envelope.
Economies of scale
can be achieved by integrating the overall building
design approach, and assuring that each exterior
architectural element complements and works with all
others. The materials used to create canopies, mansards,
sculptural fasciae and other special architectural forms
can be provided by the same suppliers who install systems
and components for roofing and exterior walls. Also,
installation can be done by the same crews using similar
equipment, minimizing jobsite complexity and construction
delays.
Prepainted
Galvalume sheet, used for such applications, helps assure
superior performance and appearance, not just in the
crucial building envelope, but throughout the project.
The main elements and details can be designed to function
as parts of a total architectural system.
Copings, rake
edges, gravel stops and trim: Frequently, a project
designer's work is allowed to end once the basic design
approach has been established; the rest is left to
detailers. But fulfillment of an overall design concept
often lies in the successful execution of the details.
Here, too, prepainted Galvalume sheet can offer special
design advantages.
All of the
"little elements" -- trimwork, stops, copings
and others -- which are critical to accomplishing the
overall design effect, can be executed using the same
materials, treatments and colors that are used for
coverage of larger exterior areas. The technical problems
of transitions, seaming and joinery are minimized by
using identical materials. Of equal importance, designers
can be certain that awkward, unsightly or technically
inappropriate details won't spoil a project's appearance
or undermine design intent.
Extensive testing
confirms top quality
Research engineers
at Bethlehem developed Galvalume sheet in the mid-1960s.
Introduced commercially in 1972, it has enjoyed the
fastest growth rate of any steel product on the world
market.
The long-lasting
resistance of bare Galvalume sheet steel to atmospheric
corrosion is well established throughout the metal
building industry. Results are conclusive: Bare Galvalume
sheet is at least two to four times more resistant to
atmospheric corrosion than G90 galvanized sheet�and at
least comparable to aluminum-coated Type 2 sheet in
durability�while providing superior galvanic protection
and crevice corrosion resistance.
It is not
surprising, then, that prepainted Galvalume sheet is also
demonstrating excellent resistance to corrosion. In
laboratory tests, as well as in controlled, real-life
tests throughout the United States, prepainted Galvalume
sheet outperforms prepainted galvanized G90 sheet.
Flexibility and
paint adherence
The accompanying
photographs below are 1.3 x magnification views of
prepainted sheet deformed by an 80-inch-pound reverse
impact. A tape-pull has been used to evaluate the paint
adherence after deformation. Prepainted extra-smooth
Galvalume sheet is on the left and prepainted
minimized-spangle, extra-smooth galvanized sheet is on
the right. Both substrates were painted with the same
primer systems and topcoats. The Galvalume sheet was
painted with a chromate pretreatment, while the
galvanized sheet was painted with a complex oxide
pretreatment.
Prepainted
Galvalume sheet is seen to be less susceptible to
micro-crazing and loss of paint adhesion during forming.
This finding is consistent with laboratory forming
evaluations which have demonstrated that the 55%
aluminum-zinc coating can withstand higher strain levels
before a crack penetrates to the base steel, compared to
a 100% zinc coating. Thus, prepainted Galvalume sheet can
more easily accommodate the strains encountered in
typical roll forming operations used to manufacture metal
panel components. Such paint formability benefits are
important for protection against atmospheric corrosion.
Eight-year
atmospheric exposures
After eight years
exposure at four different test sites, prepainted
Galvalume sheet exhibits superior overall performance
compared to prepainted galvanized G90 sheet. Each
material was painted with Bethlehem-approved paint
systems. The only difference in processing was the use of
a chromate pretreatment for Galvalume sheet versus a
complex oxide pretreatment for the galvanized sheet.
Galvalume sheet
vs. galvanized sheet
At the relatively
severe Kure Beach, NC exposure site, 250 meters from the
surf of the Atlantic Ocean, prepainted Galvalume sheet,
left, exhibits excellent corrosion protection along a
scribe used to simulate panel damage. By contrast, the
galvanized G90 sheet, right, exhibits light rust staining
and the onset of paint creepback from the scribe. Also of
concern, is the appearance of micro-blisters over the
entire surface of the sheet. (Photographs below are at 4x
magnification).
Edge creep
Edge creep can be
defined as paint undercutting along sheared edges on
prepainted metal sheets. Bethlehem's prepainted Galvalume
sheet exhibits consistently minimal edge creep which
tends to taper off to less than a millimeter after eight
years exposure at our most corrosive test site. (See
following chart.) Adherence to Bethlehem's Process
Specification is reflected in this excellent, long-term
behavior.
By contrast,
galvanized G90 sheet, prepainted with conventional paint
systems, exhibits more variable edge creep performance.
The overall range of edge creep corrosion has also begun
to increase beyond 6 years exposure
.
Bethlehem
Technical Bulletins
As with all
materials of construction, there are guidelines for
obtaining optimum performance in the field. The Technical
Bulletins listed below have been developed by Bethlehem
engineers to provide guidelines for the proper
application of prepainted Galvalume sheet components.
• Field
Painting of Galvalume Sheet, TB-200A
•
Guidelines for Welding Galvalume Sheet, TB-201
• Design,
Construction and Maintenance Guidelines for Galvalume
Sheet, TB-203
•
Compatibility of Materials used in Metal Building
Construction, TB-204A
• Coating
Weight and Thickness Designations for Coated Sheet
Steels, TB-205
•
Preventing Wet Storage Staining of Galvalume Sheet,
TB-206
• Fastener
Selection Guidelines for Use with Galvalume Sheet,
TB-207A
•
Performance of Galvalume Sheet in Animal Confinement
Applications, TB-208
Warranties
Warranties are
available to cover base metal and paint systems.
Bethlehem offers standard paint protection warranties of
three years (white roofing applications) and five years
(white and color siding applications) on its prepainted
Galvalume sheet. Longer warranties are available from the
paint supplier and coil coater.
In addition,
subject to the terms of the warranty, the base metal of
prepainted or unpainted Galvalume sheet roofing or siding
is guaranteed by Bethlehem not to rupture, fail
structurally, or perforate due to corrosion for a period
of 20 years and 6 months. The warranty assumes that the
material is used in accordance with the manufacturer's
instructions. Contact Bethlehem for more details
concerning the warranty available for prepainted
Galvalume sheet.
Design resources
Helpful design
resources are available on the use of metal architectural
systems and components, a number of which are listed
below. You are encouraged to consult these resources for
additional technical information.
1. Architectural
Design Guidelines
"Architectural
Design and Planning Guidelines," Building
Systems Institute, 1230 Keith Building, Cleveland,
Ohio 44115.
Vonier, Thomas:
"Beyond Shade and Shelter: Pre-engineered Metal
Building Systems," Progressive Architecture,
March 1982.
2. Structural
Design and Wind Loading Specifications
"Specifications
for the Design, Fabrication and Erection of Steel for
Buildings," American Institute for Steel
Construction.
"Specifications
for the Design of Cold-Formed Steel Structural
Members," American Iron and Steel Institute.
"1986 Low
Rise Building Systems Manual," Metal Building
Manufacturers Association, Cleveland, Ohio.
"Class 90
Rating for Wind Resistive Construction,"
Underwriters Laboratories.
3. Materials
Specifications
Galvalume sheet
is described in American Society for Testing and
Materials (ASTM), Designation A792, and is usually
ordered in one of two coating classes: AZ50 or AZ55.
Bare and
prepainted Galvalume sheet steel have been
incorporated with guide specifications for metal
building systems and components by the U.S. Army
Corps of Engineers. The applicable specifications are
CEGS-07413, CEGS-07415 and CEGS-13120. Prepainted
Galvalume sheet is also recognized in the Department
of Navy guide specification NFGS-13121.
4. Additional
Contacts
A significant
advantage to users of metal building systems and
components is the availability of expert, experienced
technical advice and consultation, usually when and
where it is needed, and at no charge. Each of the
organizations listed below offers design assistance
and technical consultation. Each will also provide
information on the availability of products that
match specific project requirements.
Metal Building
Manufacturers Association, Cleveland, Ohio.
Metal
Construction Association, Washington, D.C.
Building
Systems Institute, Cleveland, Ohio.
Systems
Builders Association, Arlington, Texas.
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