The mechanical method is basically rolling the metal bits in a tumbler with zinc and glass balls after flashing them with copper. This method achieves the middle thickness of zinc of the three methods but the bond between the rounded pieces of zinc are very weak
Imagine a bolt outside holding your kid's playhouse together. The pretty bright shiny bolt is electroplated with zinc while the hot dipped galvanized is dull. Come back next year and the shiny bolt is rusted and can give your kids tetanus.
Zinc is a sacrificial metal that gives itself to the steel to protect it from rust. If the steel rusts it won't be there to do its job and as it weakens it will make everything ugly with stains.
Electroplating results the absolute minimum amount of zinc over the metal as possible while hot dipped galvanizing, a very redundant term, allows for the most amount of zinc possible. At over 800 degrees, as this is a molten metal, several layers of protection occur. The first three layers are an iron/zinc allow that are actually harder than the steel base while the outside layer is pure zinc. If the zinc is ever scratched or compromised, a flash rust spot will occur but the zinc's electrons will sacrifice themselves to prevent further degradation. The zinc will migrated up to 1/4" to heal the wound in the coating. That is why zinc acts like an anode to steel, sacrificing itself to protect the nail.
The top layer of zinc, or forth, reacts with oxygen to become zinc oxide, which reacts with carbon dioxide, which becomes zinc carbonate. This patinas to a gray color and forms a crystalline structure referred to as a spangle. This process leaves about 50 microns of zinc as opposed to the 3 microns, yes three, that electroplating leaves. Ant those three microns are of inferior quality to the fifty that hot dipped galvanized have. In fact, we offer a double hot dipped galvanized steel roofing nail.
The choice boils down to an electroplated nail with about three microns of pure zinc or a four layer coating of zinc alloys 50 microns thick. Which do you think will pass the salt fume test better, the electroplated nail struck by a pneumatic driver blade and over driven or a hot dipped nail planted by a roofing hatchet that is only driven flush?
Senco claims it nailer with a hardened blade delivers 884 pounds of power per square inch. The regulator can take that down to about 70 to 120 in/lb. Since the nail head is only about 1/10 of a square inch, and I'm guessing, then that is up to 1200 foot lbs into the nail head if the driver is not worn. That will knock the zinc out of anyone.
FYI, many architects require hot dipped galvanized nails on open bottom structures without soffits because they don't want the rust showing up underneath.
Ask your roofer to bring you a sample of his nails. If they are shiny, there is not enough zinc to protect the steel. If they are dull, like the nails you remember, they are like the nails you remember.
Ask your roofer if he uses nails made by Chinese political prisoners or free Americans. Ask if they are hot dipped galvanized or electroplated. Ask who made them. Ask if the nail is important or not.
Why don't roofers use these better nails more often? Guess.
Jon Alan Wright
Jon Wright Roofing, Siding, and Windows
1915 Peters Rd., Suite 310
Irving, TX 75061