Regular News Bulletin of Conspectus Inc. addressing design & construction technical issues

1. NEWS BULLETIN
www.conspectusinc.com
Vol 09.10.01 ©2009 Conspectus Inc.
Experience, Quality, & Value Beyond Words
Page 1 of 2
Providing:
Specifications, Quality Assurance, Zinc Coatings and Metal Studs
Inspections & Investigations
for your Construction Projects By Justin Lane, CSI, SCIP
ABSTRACT: Introduction
The zinc coating selection and There are many different types of The steel passes into the heating
thickness for metal studs requires zinc coatings available. The major or annealing furnace to soften the
knowledge of the corrosiveness of galvanized types are batch hot-dip steel and impart the desired
the environment in which the galvanizing, continuous sheet strength and formability.
product will be used and the code
galvanizing, zinc plating,
requirements for the proper In the furnace, the steel is
coating type and weight. electrogalvanizing, mechanical
maintained under a reducing gas
plating, zinc spraying, and zinc
atmosphere to remove any oxide
FILING: painting.
that may be on the steel surface.
UniFormat™ This article will discuss continuous
The steel then passes through a
B2010 - Exterior Walls sheet galvanizing which is the
vacuum chamber to the molten
C1010 - Partitions predominant method used on
zinc coating bath to prevent any
sheet steel for structural and
air from re-oxidizing the heated
MasterFormat™ nonstructural steel studs.
steel. The steel sheet is sent
05 54 00 - Cold-Formed Metal The hot-dip process for around a submerged roller, which
Framing. continuous sheet galvanizing reacts with the molten metal to
09 22 16 - Non-Structural Metal produces four different types of create the bonded coating.
Framing coated products, including
The steel is then removed in a
(G)-zinc, (A)-zinc-iron alloy,
KEYWORDS: vertical direction and high
(AZ)-55% aluminum-zinc alloy,
pressure air is used to remove any
Stud, Coating, Continuous Sheet and (GF)-zinc-5% aluminum alloy.
excess molten zinc to create a
Galvanizing, Hot-Dip, Zinc,
Galvanized In North America there were controlled coating thickness.
approximately 85 hot-dip lines in
The steel is then cooled to allow
REFERENCES: 2004. Each could apply at least
the zinc to solidify onto the steel
one of the coatings listed above.
ASTM A653 - Standard surface before the steel contacts
Specification for Steel Sheet, Zinc- another roller to avoid transferring
Coated (Galvanized) or Zinc-Iron or damaging the coating.
Alloy-Coated (Galvannealed) by Continuous Sheet
the Hot-Dip Process
Galvanizing Process Selecting the Correct
The molten coating is applied onto
Coating Thickness
ASTM A1003 – Standard
Specification for Steel Sheet, the steel surface by passing a Although hot-dipped galvanizing
Carbon, Metallic, and Nonmetallic continuous ribbon of steel through is available in a variety of coating
– Coated for Cold Formed Framing a bath of molten zinc at speeds up weights ranging from G01 to
Members to 600 feet per minute. Sheet size G360, the steel stud industry
can range from 0.010 to 1.70 typically offers three standard zinc
ASTM C645 - Standard inches thick, and up to 72 inches coatings G40, G60, and G90 with
Specification for Nonstructural wide. 0.40, 0.60, and 0.90 total ounces
Steel Framing Members
The coating process begins by of zinc per square foot,
cleaning the steel with alkaline respectively, applied to both sides
ASTM C955 - Standard of the sheet metal. The standard
Specification for Load-Bearing liquid combined with brushing and
followed by rinsing, and drying of coatings requirements for
(Transverse and Axial) Steel Studs,
the steel. structural products are listed in
Runners (Tracks), and Bracing or
Bridging for Screw Application of ASTM C955 and nonstructural
Gypsum Panel Products and Metal products are found in ASTM C645.
Plaster Bases

2. NEWS BULLETIN
www.conspectusinc.com
Experience, Quality, & Value Beyond Words Vol 09.10.01 ©2009 Conspectus Inc.
Page 2 of 2
The metallic coating requirements Figure 1 shows the estimated
for structural studs can be found service life for the various coating Conclusion
within ASTM C955 Table 1. The thicknesses, assuming full
table lists three coating exposure during the life cycle. Understanding what galvanized
designators CP40, CP60, and CP90 (Illustration used with permission coatings are available is the first
that permit coatings using any one from www.galvinfo.com.) step in selecting what coating is
of the four galvanizing types. right for your product and project.
ASTM C955 states that structural Identifying Studs in We suggest the following as the
minimum coatings based on use:
studs must have a minimum the Field
protective coating CP60. The CP60 Exterior Walls: G90; Interior Wet
designator requires G60 as the Most Architects don't carry
Areas: G60; and Interior Dry Areas:
minimum zinc coating or A60, micrometers to the field to check
G40, the default by ASTM C645.
AZ50 or GF30, the equivalent of metal thicknesses. A disk
the other permitted coatings. micrometer is required for use on Be sure to take advantage of your
dimpled studs produced by many product reps to assist in selecting
For ASTM C645 nonstructural manufacturers today and will also the correct coating thickness for
studs, a minimum G40 zinc work on flat studs. your metal studs, especially for
coating conforming to ASTM A653 unusual conditions. For additional
is required. The standard also The International Building Code
information to help select coating
allows other protective coatings (IBC) 2006 and 2003, for both
thicknesses, refer to the GalvInfo
with an equivalent corrosion structural and nonstructural
Notes series of documents.
resistance. products, by referencing ASTM
C955 and ASTM C645, require that
When extreme humidity, salt spray all studs and tracks be labeled at a
or corrosive environments are maximum 96 inches on center.
anticipated, a G90 coating weight The marking must show the
is recommended, which most manufacturer's identification,
manufacturers offer as a special minimum uncoated metal
purchase item. It is important to thickness, minimum yield strength The information contained in this
remember that for all continuously document is offered for educational
(ksi) and coating type and weight. purposes, only, and not as technical
galvanized sheet materials, the advice suitable for any particular
coating weight is given as the total Therefore, if the product is not project or specific condition. Technical
marked, it is not code consulting is unique to the facts of a
zinc weight for both sides of the
compliant material and should particular condition, and Conspectus
sheet. This coating weight is not not even be allowed on the recommends that a specialist be
necessarily evenly divided between jobsite. consulted to determine solutions for
both sides of the sheet. each specific condition.