| Author |
Message |
Nathan Woods, CCCA, LEED AP
Senior Member
Username: nwoods
Post Number: 399
Registered: 08-2005
| | Posted on Friday, November 04, 2011 - 07:07 pm: |    |
I have received a submittal for a repair product intended to "paint" over field welded galvanized steel members to repair the galvanic coating that is destroyed during the welding process.
The repair material is 95% zinc in the dry film using only Type III “ultra pure” ASTM-D-520 zinc (lead and cadmium free)and claims to be "recognized under the Component Program of Underwriters Laboratories, Inc. as equivalent to hot dip galvanizing."
It further claims that it "Meets and exceeds Fed. Spec. DOD-P-21035A (Galvanizing Repair Spec);
MIL-P-26915A (USAF Zinc Dust Primer); ASTM Des. A-780 (Standard Practice for Repair of Damaged Hot-Dip Galvanized Coatings; SSPC-Paint 20
(Specification for Zinc-Rich Primer).
That all sounds well and good, but I simply want to know, if I coat a piece of steel with this product, is the resulting galvanic protection comparable to rest the G90 galvanized members surrounding it? |
J. Peter Jordan (Unregistered Guest)
Unregistered guest
| | Posted on Saturday, November 05, 2011 - 11:59 am: | |
We used to describe such products as "zinc rich" paints and I have been specifying such products on almost every project I have specified since 1979. I am actually a little surprised that they are 95% zince in the dry film; just seems like there ought to me something else in it (maybe more resin?).
There may be field-applied products out there that are better than hot-dipped zinc coating, but they are probably more expensive and difficult to deal with. However, when you must work with a zinc-coated product to get it installed, you need somethng, and historically, the zinc rich coatings have been it.
Sometimes, I find myself taking a close look at a product that I have been specifying for years and years, and being a little surprised at what it actually is. |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 101
Registered: 12-2006
| | Posted on Wednesday, November 09, 2011 - 09:40 am: | |
I typically just require compliance with ASTM A780 which this product claims to do.
Whatever happened to the good old days when welders just used zinc sticks at welds and melted real zinc onto the weld spot while it was still hot? Does anyone see this any more? |
Nathan Woods, CCCA, LEED AP
Senior Member
Username: nwoods
Post Number: 400
Registered: 08-2005
| | Posted on Monday, November 14, 2011 - 04:46 pm: | |
Thanks guys. I approved the "ZRC Galvilite Galvanizing Repair Compound" that was submitted for repair of field welded shop galvanized materials. |
Ronald J. Ray, RA, CCS, CCCA
Senior Member
Username: rjray
Post Number: 88
Registered: 04-2004
| | Posted on Wednesday, November 16, 2011 - 08:34 pm: | |
I am a bit late, but I believe ZRC was the originator of the galvanizing repair coatings.
I am not sure what your application is, but for what it is worth, my specifications do not allow field welding of galvanized components. |
Nathan Woods, CCCA, LEED AP
Senior Member
Username: nwoods
Post Number: 402
Registered: 08-2005
| | Posted on Wednesday, November 16, 2011 - 10:21 pm: | |
"for what it is worth, my specifications do not allow field welding of galvanized components"
Mine don't either, but then there is reality..... |
Ronald J. Ray, RA, CCS, CCCA
Senior Member
Username: rjray
Post Number: 89
Registered: 04-2004
| | Posted on Thursday, November 17, 2011 - 09:09 am: | |
Part of reality is ensuring during the submittal phase that only mechanical connections are indicated for exterior galvanized steel fabrications. |
Ellis C. Whitby, PE, CSI, AIA, LEED® AP
Senior Member
Username: ecwhitby
Post Number: 122
Registered: 03-2003
| | Posted on Thursday, November 17, 2011 - 11:54 am: | |
Ensuring that submittals are correct is "a part of reality". So is the contractor informing the Owner and the AE after the fact that the contractor made a field modification” “Is this OK?” “We didn’t think anyone would mind.” “We have always done it that way.”). Or not informing anyone and the issue is discovered later (sometimes much later). |
Nathan Woods, CCCA, LEED AP
Senior Member
Username: nwoods
Post Number: 403
Registered: 08-2005
| | Posted on Thursday, November 17, 2011 - 12:17 pm: | |
As I'm sure Mark, our resident structural engineer here on 4specs can affirm, a welded connection is many times stronger than a bolted or rivoted connection. Stronger connections result in smaller members/flanges/plates, etc... Not to mention that hot-dip galvanization requires components to fit into the tank... ever galvanized a 210' girder?
I'm merely saying that "reality" extends way beyond the discussion of "fault" or responsiblity. |
Mark Gilligan SE,
Senior Member
Username: mark_gilligan
Post Number: 429
Registered: 10-2007
| | Posted on Thursday, November 17, 2011 - 05:42 pm: | |
The question is not so much what is stronger because some bolted connections can be sronger than some welded connection. In these situations the difficulty is that bolted connection is often not desirable since it takes up more space and may not be consistent with the use or look of the building.
Suggest that a field welded connection can have acceptable corrosion performance. While the field welded connection may not be as good as one galvanized in the shop it may be perform acceptably. If you look at the galvanizing standards I believe that you will find guidance for field repairing of galvanizing.
The other thing to remember is that galvanizing does not mean you will never have corrosion problems. Galvanizing has a finite life when subject to a corrosive environment. What galvanizing does is extend the time before you need to pay attention to corrosion.
In addition scratches on a galvanized part will be less critical than scratches on a painted surface. |
Richard Gonser AIA CSI CCCA SCIP LEED
Senior Member
Username: rich_gonser
Post Number: 29
Registered: 11-2008
| | Posted on Saturday, November 19, 2011 - 04:53 pm: | |
FYI, the ZRC's Galvilite will not be usable in So Cal when the next round of AQMD regs kick in.
Unfortunately, it's replacement "ZRC Zero-VOC Water-Based Cold Galvanizing Compund" has a battleship gray finish not a silvery metallic one.
If anyone knows of a silvery metallic finish one please let this 4specs world know. |
Jim Sliff
Senior Member
Username: jim_sliff
Post Number: 110
Registered: 08-2010
| | Posted on Wednesday, December 21, 2011 - 01:16 pm: | |
Richard - I've been kicking this problem around as well. I have found one possible solution but have not yet seen actual samples - I may have to find a dealer, buy some and spray it myself (something I end up doing quite often; you should see the load I take to the twice-yearly hazardous waste roundup - and the fortunately-hidden wall of our house next to the trash bins; looks like tagger heaven!).
Aervoe has a stainless steel aerosol that I'm sure will look better than ZRC's or Aervoe's galvanizing repair coatings....but using it would mean a two-step process: application of the galvanizing repair coating to get the zinc on the surface, then application (via aerosol) of the stainless steel coating to "mask" the dull gray look.
I'm not sure how practical it is, but it can't look worse than any of the "chrome" aerosol or bulk coatings, which don't look like chrome OR galvanized.
_____________________
ALERT - A tech caution from "@79specguy" (the Twitter account I use once a year or so...still have no idea how to use that system) - "Cold Galvanizing" is NOT the same thing as "Galvanizing Repair" in most cases (I've found many are not aware of this).
Many manufacturers make a cold galvanizing compound in aerosol form that is meant ONLY as a temporary coating to protect damaged/welded spots until they can be properly coated.
If you use them like you would "Galvanizing Repair" coating on a permanently-exposed surface the stuff will rust through in months. There's almost no (or a VERY cheap) binder in them; they serve one purpose - protect damaged surfaces for a few WEEKS.
I'm also concerned about the new galvanizing repair materials that are 95-97% zinc (meaning the *pigment* mix is that amount, with the balance inert, non-toxic materials not listed on the MSDS) and leave a 93% zinc film on the surface. There can't be much binder, so I *think* the intent is to no longer leave the repair coating exposed, but to coat it with something like the stainless steel coating or another metallic.
But whatever you do, don't specify "cold galvanizing compound" as an exposed finish. You might specify one of the few that's fine, but I'll but my $35 Tijuana Rolex that it'll get switched on the job (or a submittal will slip through) to one of the more common temporary coatings....and with the new "battleship gray" color of both you'll never know just looking at the surface. |
John Bunzick, CCS, CCCA, LEED AP
Senior Member
Username: bunzick
Post Number: 1348
Registered: 03-2002
| | Posted on Tuesday, December 27, 2011 - 10:53 am: | |
Jim,
your caution about types of galvanizing repair products is a good one. However, it hinges on definitions of terminology, which like most industries, is probably not standardized. Is there a technical standard, ASTM or SSPC for example, that would differentiate the products based on performance, formulation, or other criteria? That's really the best way to get the performance one wants. |
Anne Whitacre, FCSI CCS
Senior Member
Username: awhitacre
Post Number: 1227
Registered: 07-2002
| | Posted on Tuesday, December 27, 2011 - 12:23 pm: | |
and to answer your original question, a cold applied coating is not the same as the hot zinc of the G60. The hot zinc chemically bonds with the substrate and changes its composition. a cold applied zinc coating is just a coating. |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 122
Registered: 12-2006
| | Posted on Tuesday, December 27, 2011 - 12:38 pm: | |
The standard is ASTM A780 which ZRC and others claim to comply with.
This is why I was asking if anyone ever requires use of a zinc-stick. This was where welders literally took a stick of zinc, applied it to the still-hot area after welding, and melted zinc into the 'burn area'. That's how it was done in the 'old days' before coatings like ZRC became popular. Of course ZRC used to be applied by brush when it first came out. I wonder if it bound to substrates better considering the carrier was probably an alkyd based product.
Jim, isn't there a concern about galvanic action between the stainless steel and the zinc? That's often a sure failure in other applications. |
Jim Sliff
Senior Member
Username: jim_sliff
Post Number: 111
Registered: 08-2010
| | Posted on Tuesday, December 27, 2011 - 12:59 pm: | |
John - Ack! I foolishly was only thinking about the aesthetics question and am cleaning my toes via mouth at the moment (there's everyone's "ugly picture of the day").
Forget stainless. It reacts in several *other* ways with zinc - in fact, it can, in rare cases, cause a fire! I guess in a backwards way it may be a good thing that I stuck my foot in my mouth! Most (in my experience) are not aware that zinc and stainless are a very bad combination!
Also, thanks Anne for clarifying what I was trying to say - cold galvanizing that's field applied is just paint, and field quality control is usually nonexistent. The stuff is often haphazardly applied with little surface prep, sprayed or brushed onto damp surfaces, and with no verification of mil thickness. That's where the problems come up and (I'm treading thin ice...this is NOT advertising!!) why IMO field inspection/supervision of anything involving corrosion,coatings or water/weatherproofing, which is an afterthought if a thought at all, needs to be part of almost every project. |
Don Uggla (Unregistered Guest)
Unregistered guest
| | Posted on Wednesday, November 28, 2012 - 11:51 am: | |
I recently purchased a galvanized trailer (new). The galvanizer used a grinder to remove excess hot-dip debris and in some spots (small) went down to the bare metal. It's not obvious, of course, until the rust forms - after it ships. They also used zinc rich paint for touchup in several areas.
They cite standards that endorse the use of this paint, but that paint won't last long under abrasion (sand, gravel, road spray and road debris). The "standards" leave a lot of room for suppliers to justify using paint or cold galvanizing sprays. No consideration for the application.
DOES ANYONE HAVE EXPERIENCE WITH THE ZINC SOLDER STICKS ON THE MARKET? Supposedly with thorough cleaning and a MAPP gas torch the spots can be covered with a thick metallic coating. That appears to be my only option. |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 383
Registered: 12-2006
| | Posted on Wednesday, November 28, 2012 - 02:17 pm: | |
Don, a patch is a patch. Still, the zinc stick (see my comment above) might provide better protection than the ZRC-type products; keep in mind that it may not look very good as you'll be melting zinc onto the surface.
It may end up looking like the debris your galvanizer removed to begin with.
Still, I suppose that's better than looking at rust. Besides, at 60 mph, no one will notice if the patch looks a little bulky. You'll see the repair paint application too. That will probably require more frequent touchup. Keep in mind that zinc is a sacrificial coating, and a soft one at that.
Isn't the trailer still under warranty? Can you take it back and demand proper repairs? |
Don Uggla (Unregistered Guest)
Unregistered guest
| | Posted on Friday, December 07, 2012 - 02:12 pm: | |
Ken, Thanks for the feedback. I can accept a patch that looks like debris. My primary concern is durability and rust protection.
The trailer is covered by a very weak warranty. The manufacturer's response was that they have discontinued offering HDG as an option. They are providing $150 for field repairs.
The company advertizes it's high quality, engineering expertise and the best prep and paint finishing in the business. It appears that the HDG was done by a vendor and there were no QC specs. I like the trailer in all other respects,so want to keep it. I talked to two other HDG vendors who do trailer frames and they only repair with paint and sprays - which I consider inadequate.
As a former quality engineer, I suppose I should have done a salt spray test and waited for a couple of days before accepting it and towing it off the lot. As a customer, I didn't think that would be necessary. |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 387
Registered: 12-2006
| | Posted on Friday, December 07, 2012 - 02:40 pm: | |
Seems like we always take better care of our clients than we do ourselves. |
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