Hot dipped vs. zinc coated bolts

[JAE]

I'm not a coating expert - just looking for some wise perspective -

Got an exterior structure, non-marine environment, but outdoors and exposed to midwestern USA summers and winters.

These are mild bolts - A307 or A36, (not high strength A325's) that connect HDG plates to glulam wood beams.

Contractor wants to substitute a zinc coating instead of hot dipped galvanizing (which we specified) to speed up acquisition time.

I believe, from the literature I've read, that HDG would be much better but just wanted to get some concurrance from you experts out there. Any comments? Thanks in advance.

 

[JAE]

...forgot - they stated that they would coat it in two coats totalling 0.001 mils.

 

[kenvlach]

In general, plating of fasteners should only be done by the manufacturer for tolerance reasons. Shouldn't matter in your case [especially with only 0.001 mil = 1 micro-inch!!!].

HDG is usually better, but that is mostly due to greater thickness. Electroplated zinc occasionally has porosity (if buying from lowest bidder), but should be fine if 1 mil thick and yellow chromated.

 

[kenvlach]

Mechanically plated zinc, again, with yellow chromate, is fine.

Or did you mean some other type of coating (not plated)?

 

[EdStainless]

So these joints are exposed to weather?
There is a chance of water in the joints?
Go with the heavier coating of HDG.
Even those come in grades of coating you know.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[JAE]

Well, that's the problem, they didn't really specify what type of "zinc plating" (their term) they were going to use.

We've essentially decided to stick to the HDG, but I really wanted to get a quick education on this.

 

[unclesyd]

Stick with the HDG bolts. You should have no problem getting HDG fasteners in the materials you are specifying.

The quality of electrolytic or mechanically plated zinc has become a problem lately. It runs all over the place, the good, the bad and the plumb ugly.