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George A. Everding, AIA, CSI, CCS, CCCA
Senior Member
Username: geverding

Post Number: 626
Registered: 11-2004


Posted on Friday, May 18, 2012 - 02:25 pm:   Edit PostDelete PostPrint Post

Working on a Friday deadline and I need a quick reminder of the difference between A60 and G60 under ASTM 653. I understand the 60 thickness, but is A = annealed and G = galvanized?

Thanks
George A. Everding AIA CSI CCS CCCA
Ingersoll Rand Security Technologies
St. Louis, MO
William C. Pegues, FCSI, CCS
Senior Member
Username: wpegues

Post Number: 860
Registered: 10-2002


Posted on Friday, May 18, 2012 - 02:48 pm:   Edit PostDelete PostPrint Post

George,

Pasting in from the HMMA standards they have this nice explanation:

"Zinc-coated sheets are cold-rolled sheets that have been covered on both sides with a milled applied coating of zinc to improve corrosion resist- ance. The coating may be applied by various means, but in the hollow metal industry the recom- mended methods are hot-dip galvanizing. It is important to understand the proper terminology when referencing zinc-coated sheets. The term “galvannealed” or “galvanized” sheet denotes that the sheet is coated by the “Hot-dip” process. The standard referenced for hot-dipped galvanized or galvannealed sheet is ASTM A653/A653M,”Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy- Coated (Galvannealed) by the Hot-Dip Process”."

G is hot dipped galvanized
A is hot dipped galvanealed

60 is not necessarily the thickness, it relates to the weight of the coating. 60 is 0.60 ounces per square foot (G or A 50 is 0.50 ounces per square foot). This results in an 'average' thickness of 0.0005 inches.

William
William C. Pegues, FCSI, CCS, SCIP Affiliate
WDG Architecture, Washington, DC | Dallas, TX
George A. Everding, AIA, CSI, CCS, CCCA
Senior Member
Username: geverding

Post Number: 627
Registered: 11-2004


Posted on Friday, May 18, 2012 - 03:38 pm:   Edit PostDelete PostPrint Post

William, thanks. I'm slapping my forehead because of course I have HMMA, just not the ASTM. Under deadline pressure you forget where to look.

Appreciate the quick response.
George A. Everding AIA CSI CCS CCCA
Ingersoll Rand Security Technologies
St. Louis, MO
Brian E. Trimble, CDT
Senior Member
Username: brian_e_trimble_cdt

Post Number: 61
Registered: 08-2005
Posted on Wednesday, May 23, 2012 - 10:22 pm:   Edit PostDelete PostPrint Post

On a somewhat related note, we (BIA) are considering revising our Technical Notes 28B on Brick Veneer / Steel Stud walls. We have been recommending a G90 coating on steel studs for use in this wall system for years, but have gotten a lot of flack for this. Most manufacturers state that G60 is all you really need. Any comments on whether we should stick to G90 or go with the flow and make the recommendation for G60?
Sheldon Wolfe
Senior Member
Username: sheldon_wolfe

Post Number: 568
Registered: 01-2003


Posted on Wednesday, May 23, 2012 - 11:55 pm:   Edit PostDelete PostPrint Post

And then the manufacturers will say you really only need G30...

I (apparently erroneously) assumed there was either testing or empirical evidence to support BIA's recommendations.
ken hercenberg
Senior Member
Username: khercenberg

Post Number: 246
Registered: 12-2006
Posted on Thursday, May 24, 2012 - 09:20 am:   Edit PostDelete PostPrint Post

I always thought it was a 'pay me now or pay me later' option. G90 will last longer than G60. Zinc is sacrificial. It's not a question of if but of when. Seems a lot cheaper to provide it up front instead of having to tear everything out and replace it, and yes, I've had too many projects like that. Of course if the developer is looking to sell building within 5 years of building it, they will probably prefer G60. Depends on your end user.
Jeffrey Wilson CSI CCS
Senior Member
Username: wilsonconsulting

Post Number: 66
Registered: 03-2006
Posted on Thursday, May 24, 2012 - 09:20 am:   Edit PostDelete PostPrint Post

I would favor recommendations correlated w/ life expectancy. For a longer intended lifespan of the building, more robust anchor materials would be warranted. Perhaps a range of anticipated service life (derived from analysis of actual in-service conditions) associated w/ each available material (SSTL, G90 galv, G60, etc.) would be a useful guide for the specifier to select the appropriate level of protection to satisfy design goals.
J. Peter Jordan, FCSI, CCS, AIA, LEED AP (Unregistered Guest)
Unregistered guest
Posted on Thursday, May 24, 2012 - 10:27 am:   Edit PostDelete PostPrint Post

I think it would depend on the design of the wall assembly and the climate. I have always favored heavier galvanizing in the Gulf Coast region, but what makes a real difference is how much condensing humidity you can expect to accumulate in the stud wall cavity. With more attention paid to the design of exterior wall assemblies now, I am not sure this is as much a concern as it might have previously been.
ken hercenberg
Senior Member
Username: khercenberg

Post Number: 248
Registered: 12-2006
Posted on Thursday, May 24, 2012 - 11:11 am:   Edit PostDelete PostPrint Post

Actually in northern climates there needs to be concern about ice build-up occuring on the wall ties since that will presumably break down the tie over time. The other concern is that while this can create a thermal bridge by attaching thge tie to the stud, albeit through the sheathing, there should still be some 'benefit' of heat trasfer to prevent ice buildup in winter. By introducing a thermal break, do we end up with more ice buildup? Do we need to change to heavier gage galvanized steel or even stainless steel ties? I suppose with stainless steel ties there is less heat conduction than with galvanized steel.
Ellis C. Whitby, PE, CSI, AIA, LEED® AP
Senior Member
Username: ecwhitby

Post Number: 153
Registered: 03-2003
Posted on Thursday, May 24, 2012 - 11:13 am:   Edit PostDelete PostPrint Post

Peter;

Good point. If the building has say, a rain-screen wall assembly with insulation in the cavity and waterproofing/air barrier on the sheathing, in theory there should be no water or condensation on the studs. A show of hands from those who fully trust that the construction will be 100% water and air tight?
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick

Post Number: 1397
Registered: 03-2002
Posted on Thursday, May 24, 2012 - 04:44 pm:   Edit PostDelete PostPrint Post

For hollow metal doors and frames, manufacturers have told me not to worry about whether it is A or G, both will give good performance.

As to studs, I'm wondering if there is a code requirement for this. I always specified G90, but we also always specified primed structural steel. We eliminated structural steel priming given that we have very tight weather/air barriers on our buildings now so the exterior walls are much drier than has historically been the case. By the same logic, one could argue that G60 is enough these days. I doubt there is a huge price difference in any case. I probably would continue to spec G90 unless barring some convincing evidence as to cost-effectiveness of a thinner coating.
Taylor Hawkins (Unregistered Guest)
Unregistered guest
Posted on Sunday, March 17, 2013 - 07:28 pm:   Edit PostDelete PostPrint Post

I am looking to build an outdoor grill island using 18 gauge steel stud framing. The framing will be enclosed and raised off the deck floor, so it will not be directly exposed to water, though there will no doubt be moisture or condensation. I was looking to use G60 coating. Will this be adequate or should I step up to G90? (Baltimore, MD area)
ken hercenberg
Senior Member
Username: khercenberg

Post Number: 471
Registered: 12-2006


Posted on Monday, March 18, 2013 - 09:43 am:   Edit PostDelete PostPrint Post

Taylor, I think you need to assess how long you want this assembly to survive.

Even with advancements in air/water barriers, sheathing, "continuous insulation" and similar advancements, It seems unbelievable to me that anyone would consider dialing back the most basic portion of their assembly. If your studs fail, your project is gone. With so many variable offerig potential for failure it seems like a very cheap insurance policy to pay the difference between G60 and G90.

Once again our industry seems to want to look in the wrong places for cost savings. We keep putting smaller lifeboats on the unsinkable Titanics and then wonder why we still have disasters.
J. Peter Jordan
Senior Member
Username: jpjordan

Post Number: 540
Registered: 05-2004
Posted on Monday, March 18, 2013 - 10:50 am:   Edit PostDelete PostPrint Post

I believe that the G90 coating for steel sheet is a coil coating. Nonetheless it is a coating of steel sheet before fabrication. With steel sheet, there are several fabrication processes that it takes to make it into not just a stud, but a stud wall. Pay attention to the connections especially the ones that penetrate or otherwise damage the zinc coating.

One can see a lot of galvanized steel stuff in seafront areas that has withstood the test of time satisfactorily; however, a lot of this stuff is hot-dipped galvanized after fabrication. I have specified hot-dipped galvanizing for exposed structural steel at the Port of Houston. I know that there are problems, but this approach is not uncommon.

For the application described by Mr. Hawkins, I would go to G90, but I would also pay careful attention to the specifications and field quality control for repair to galvanizing.

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