Post-Cast Anchors in Outdoor Applications

[P1ENG]

I've searched for my answer, but it seems past discussions never anchored down an opinion (pun intended).

I have clients always upset that I make them switch their hot-dipped galvanized, post-cast mechanical anchors for stainless steel when the anchor is located outdoors. I always reference the ICC ESR (regardless of anchor brand as they all have this similar verbiage) that use of zinc-coated carbon steel anchors are limited to dry, interior locations. They always claim that HDG is not the same as zinc plating, and I agree as plating is thin and doesn't offer the zinc/steel bonding that HDG provides. But the report doesn't say "plating". It says "zinc-coated". And regardless of the process, HDG is still coating the anchor in zinc, just thicker/better bonding. Some ESR's will even state "... stainless steel anchor is permitted for exterior exposure or damp environments." So, per the report, there are (2) options: zinc-coated or stainless. If they wanted to allow HDG anchors outdoors, then they would change the wording in the conditions of use to read "stainless steel and HDG anchors are permiteed for exterior exposure". Therefore, I always say they need stainless to be compliant. Normally, the client will (understandably) balk because of the price difference but ultimately will change the anchor since I'm sealing it. But I know I'm not making friends, so I'm doing my due-diligence to make sure HDG is meant to be included in the "zinc-coated" limit state. I'm hoping there is a more codified answer/explanation to this issue to remove my interpretation from upsetting the clients.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[canwesteng]

Well, it comes down to you as the EOR. Would you allow HDG cast in anchors? I don't think it's any different to that, as the passivating effect of the concrete is unlikely to protect all the exposed anchor.

 

[dik]

I spec HDG Hilti anchors often... maybe several times a week. Both mechanical and adhesive...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[WesternJeb]

Theoretically, I agree with you P1ENG. However, my firm has spec'd out HDG anchors for external use for 25 years and we haven't had any issues yet. I have seen rusted anchors and base plates like everyone else but the important thing to note is that the surrounding metal is rusted an equal amount. If you aren't specifying stainless steel for all of your other metals, I don't see a point in specifying SS anchors.

 

[P1ENG]

canwesteng:
I agree, I err on the side of being conservative if my seal is going on it. But yes, I would allow HDG cast-in because in my mind I've decided that zinc post-cast is specifically excluded because the wedge/expansion action of the anchor would scratch the coating and provide an avenue for water corrosion.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[P1ENG]

WesternJeb,
Per your last sentence, my argument would be that the hole in the concrete would allow pooling of water and protection against evaporation. So an anchor can be sitting in water. So, not requiring stainless for base plates makes sense to me. But I'm only playing devil's advocate.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[Eng16080]

I just looked at ESR-4868, for Hilti HIT-HY 200 adhesive anchors. Section 5.17 reads: "Use of zinc-plated carbon steel threaded rods or steel reinforcing bars is limited to dry, interior locations." So, in this case they do use the term "zinc-plated". The next section mentions the use of HDG or stainless steel as being acceptable for exterior exposure or damp environments.

In general, though, I agree with your approach. Having read through some of these ESRs myself it becomes clear real fast that the marketing material for these products implies a more superior product than the story the ESR tells. (Anybody else notice how these anchors aren't permitted to support fire-resistive construction? I never would have known that if not for reading the ESR.)

 

[P1ENG]

Eng16080:
This further solidifies my opinion. ICC knows the words "plated" and "coated" and can use them as needed. Your example though is for adhesive and I am specifically concerned with mechanical anchors. I will also tell my clients that in lieu of the stainless steel wedge anchor, they could use a HDG epoxy anchor as most ESRs for adhesive anchors do not exclude their use outdoors, but I think think they prefer the stainless wedge over HDG epoxy due to installation labor and/or set/cure times.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[Eng16080]

P1ENG,
Even in that case, you have to be careful with the particular anchor that you use with the Hilti HIT-HY 200 adhesive. Hilti has proprietary anchor rods, the HIT-Z and HIT-Z-R. The HIT-Z-R is stainless steel, but the HIT-Z has a "zinc electroplated coating." So, the HIT-Z is not HDG and should not be used outdoors. I would probably use an HDG F1554 anchor rod or the stainless steel HIT-Z-R in this case.

 

[WesternJeb]

P1ENG, that is a valid counterargument and this is definitely something I will keep in mind from here on out! Great points brought up.

 

[JLNJ]

I believe the expansion wedge in Hilti's zinc coated Kwik Bolt system is stainless steel (or at least it used to be). This always gave me a little consolation that the wedge mechanism would be more or less permanent, even if exposed to moisture.

 

[P1ENG]

JLNJ,
I think that is the case with most of the sleeve anchor manufacturers. The metal sleeve in contact with the concrete is stainless regardless of the material of the threaded portion of the anchor. So that likely debunks my theory of scratching the zinc coating during the expansion process. I still don't know what I'm going to do on future jobs, but I am going to allow the anchors of this particular job (MKT Super Studs) to be hot-dipped galvanized because I talked to MKT and they are willing to provide a letter accepting liability for installing HDG anchors outside as they are pretty confident of the coating in an exterior application.

Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant

 

[Tomfh]

Zinc coated generally refers to thinner zinc coatings, i.e. electro-coated bolts, e.g. this sort of thing:

https://nutandboltshop.com.au/shop/...hors/m20-x-260-chemical-anchor-stud-set-zinc/

As opposed to hot dip gal:

https://nutandboltshop.com.au/shop/...chors/m10-x-130-chemical-anchor-stud-set-gal/

HDG is perfectly acceptable in normal outdoor environments.

If using stainless you can introduce galvanic corrosion problems. Stainless anchors often attack galvanised steel structures. Weve seen attachments fail when the stainless anchors destroy the base metal that they were fixing.

 

[dik]

Unless interior, I would never use electroplated zinc... you may as well use nothing... always HDG.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[canwesteng]

Ok, I misunderstood. Would probably agree with you that wedge anchors should be stainless and the structure should be painted for exterior applications, or HDG epoxy anchors with HDG structure/painted structure.

 

[bones206]

If using stainless you can introduce galvanic corrosion problems. Stainless anchors often attack galvanised steel structures. Weve seen attachments fail when the stainless anchors destroy the base metal that they were fixing.

I have to see if I can dig up my old details, but when I used to work on water treatment plants I believe I ended up specifying neoprene isolation bushings and washers for HDG attachments with stainless steel anchors.