Which - Galv or Zinc plated screws

[seasickstevie]

Looking for screws for outside structural support. Hoping to find coachbolts that will never rust.

The choice seems to be galvanized or zinc plated.

Price doesn't seem to be an indicator as they're virtually the same (in the sheds).
So which would last the longer?

 

[JohnD]

stainless.

 

[freddiemercurystwin]

Galvanizing is zinc plating, that is to say, they are both the same!

 

[seasickstevie]

... they are both the same!

duh!

How did I know that would be the explanation!

Just seems odd that the same sizes from same manufacturer are in different packs. One marked galv, the other zinc.

I'll see if there are any stainless.

 

[Nige F]

Galvanizing is dipping in molten zinc--- plating is electro deposition of zinc

 

[JohnD]

I'll see if there are any stainless.

http://www.screwfix.com/search.do;j...s+stainless&searchbutton.x=9&searchbutton.y=6

 

[ajrobb]

What are Wickes exterior coach bolts like? They seem to be ceramic coated.

In http://www.greatsouthernwood.com/uploadedFiles/Fastener_71706.pdf it mentions:

"* Electroplated galvanized fastener and metal products are typically not accepted by the building codes for use in exterior applications,
regardless of the type of wood used."

Probably USA, but points towards stainless.

 

[JohnD]

all than BZP or Galvanising does is defer the rust. The zinc corrodes away, depending on weather, air pollution and exposure it takes a longer or shorter time, then the steel goes. Nuts, bolts and screws tend to have the coating knocked or scraped off on the heads when you are doing them up. I use galvanised studding on my fence posts and give it a coat of paint from time to time, this protects the exposed zinc, and as I apply Copaslip to the threads, they can be undone when repairs are needed, but they still get rusty in time as exposed to the weather. Galvanised fixings used indoors in dry conditions last much better.

Makers of galvanised iron roofing sheets can actually estimate how many years it will take, depending on where you are and the thickness of the coating.

This one is about due for replacement

View media item 15096

 

[ajrobb]

Nuts, bolts and screws tend to have the coating knocked or scraped off on the heads when you are doing them up.

I agree with the general sentiment that galvanising is only a temporary protection. However, the zinc plating does not need to be complete to protect the bolt. The protection is electrical rather than physical. Small nicks and scratches are not important. Consider, an entire steel ship is protected by relatively small lump(s) of zinc (sacrificial anode).