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Mon Nov 12, 2007 11:34 pm

Hello-

I've been reading about the protection zinc plating provides - all for a relatively low cost. If this is true, is there a reason I shouldn't plate everything I can? More specifically, will I have problems painting plated parts?

Thanks,

Paul

Fri Nov 30, 2007 9:30 pm

Aside from the cost, there is no reason I know of not to zinc plate your body panels. Some modern cars are zinc plated at the factory.

Zinc works by becoming a sacrificial anode. It is more reactive than iron (i.e. the major component of steel) and corrosive elements will bond with it (and hence be neutralized) before they will bond with the iron in your car. The zinc will be consumed in this process and after a period of time the zinc will be eroded to the point where it no longer protects the steel (how long this takes is a function of how corrosive the environment is and how thick a layer of zinc coating you have). If there is an additional protective coating over the zinc (such as primer and paint) then the zinc will be protected and will hang around much much longer to protect the steel. A decent coating of zinc covered by a good epoxy primer and good quality paint would last a very long time indeed, even in particularly corrosive environment like near the ocean.

It should be possible to get a primer to stick to zinc. You should consult a paint rep for more information. You might consider putting a coat of zinc chromate primer on the zinc coated steel, with an additional coat of epoxy primer then color coats. You car would be extremely well protected.

If you wanted to go even a step further, you could try to passivate the zinc coating. I think you can do this with a solution of phosphoric acid (available at Home Depot as Ospho). This would convert a very thin layer of zinc at the surface to zinc phosphate. Zinc phosphate is fairly non-reactive (hence it is called passivated) and is a good material for primer to stick too. Since this zinc phosphate layer is not reactive it forms a barrier that will protect the zinc and steel but unlike a coating like paint it will be chemically bonded to the zinc and therefore won't be inclined to chip off. Doing all this would be like wearing two belts and several sets of suspenders.

If you do all this make sure you use zinc coated fasteners to attach the body panels (like the fender bolts and washers) or you might even consider stainless steel hardware.

This is probably way overkill when it comes to protecting the car, but if you've got the money and it makes you happy then go for it.

Sun Dec 02, 2007 10:54 am

gimmesomeshelter wrote: Hello-

I've been reading about the protection zinc plating provides - all for a relatively low cost. If this is true, is there a reason I shouldn't plate everything I can? More specifically, will I have problems painting plated parts?

Thanks,

Outrageous :!: The total elimination of rust or the possibility of rust on a vintage Volkswagen flies in the face of everything that is holy in VW ownership.

Gone, that heart-sinking moment when you get the bargain buy home only to find it's held together by bodo, pop-rivets and zip-ties.

Gone, the lonely hours spent in a cold garage cutting out that ever expanding small patch of rust you thought could be remedied in half a hour.

Gone the dodging of fast moving traffic on the highway while you retieve that precious rare part that has finally fallen from your "someday showcar".

Rust is an intrinsic and important part of the hobby...it's character building, it's fashionable, it's that inexpensive accessory that everyone can afford.

I'm all for rust...as long as it's someone else's. :D

All modern cars are galvanised...go for it. :lol:

Sun Dec 02, 2007 2:21 pm

Priming over zinc is not a problem... I've never considered zinc priming a whole panel, but I use a zinc primer as a weld through primer.

For a good weld you need clean steel, but using a zinc weld through primer allows a protection coat and still allows good penetration.

Although zinc plating may be a whole different game than a zinc primer...

Mon Dec 03, 2007 7:27 pm

Zinc plating is done with heat. I do not know the temp, but it could warp panels. Also, the last stage in zinc plating is oil quenching. Basically, they cover the entire surface with oil. If your going to be painting, you want to make sure to tell the plater to not quench.

Here is a guy who documented his zinc plating experience on a Chevelle.

http://www.einstyn.com/einstyn-hardtop-02.htm

Mon Dec 03, 2007 8:20 pm

MedicTed wrote: Zinc plating is done with heat. I do not know the temp, but it could warp panels. Also, the last stage in zinc plating is oil quenching. Basically, they cover the entire surface with oil. If your going to be painting, you want to make sure to tell the plater to not quench.

Here is a guy who documented his zinc plating experience on a Chevelle.

http://www.einstyn.com/einstyn-hardtop-02.htm

This is not completely true. There are basically two ways to zinc coat steel.

1.) Hot dip galvanizing. This is just what it sounds like. The item is dipped in a molten bath of pure zinc. Zinc melts at 787 degrees F. This is the process used on nails used for roofing and other purposes to protect them from rusting. Unless you do other finishing processes like hot air leveling the surface finish you get from hot dipped galvanized is typically somewhat rough.

2.) Zinc electroplating. In this process the item is dipped in a tank of electrolyte (usually a mild acid ) and a zinc electrode is used as the source for the zinc. An electric current is passed through the electrode and electrolyte and zinc is plated onto the item. This is done at close to room temperature, certainly at a temperature well below that which might warp a panel. The surface finish is smooth if the plated item has a smooth finish (i.e. the final finish is dictated by the finish of the item before plating).

Hot dip galvanizing would be appropriate for large frame members (like a frame head) as these items have sufficient mass and stiffness to avoid warping. If you are talking about zinc coating the unitized portion of a Bug body (like the body core, fenders, hood, trunk, etc.) then you are looking at zinc electroplating. The pan is sort of in between these two extremes but I suspect that the metal thickness here would be more appropriate for electroplating.

I have zinc plated small items by electroplating. You can buy kits from places like www.caswellplating.com to do zinc electroplating but I suspect a commercial plater would be more cost effective for something the size of a car.

Mon Dec 03, 2007 9:44 pm

Kombi wrote: Priming over zinc is not a problem... I've never considered zinc priming a whole panel, but I use a zinc primer as a weld through primer.

For a good weld you need clean steel, but using a zinc weld through primer allows a protection coat and still allows good penetration.

Although zinc plating may be a whole different game than a zinc primer...

Priming with a zinc rich primer and zinc plating bare metal are two different animals. They both use zinc to act as a sacrificial anode to chemically "tie up" corrosive elements that would otherwise bond with the iron in the steel to form iron oxide (rust) and other corrosive products.

Zinc rich primer is a primer which has very small particles of zinc suspended in an otherwise conventional primer. This offers improved protection over a conventional primer which does not offer this sacrificial anodic property.

Better than a zinc rich primer is actually applying a pure zinc coating directly onto the bare steel. This can be done either through hot dip galvanizing or through zinc electroplating (see my earlier post). Zinc coating of bare steel is superior in that both hot dip galvanizing and (to a somewhat lesser extent) zinc electroplating have a "self healing" property. If you scratch through the zinc coating down to bare steel the zinc surface crystals will actually migrate (i.e. grow) over time to cover the exposed metal. This effect is dependent on the thickness of the coating and the way it is applied. Hot dip galvanized coating will have the most pronounced self healing effect but moderately thick zinc electroplating will also exhibit this action, with the thicker the coating the more effective.

Scott

Mon Dec 03, 2007 10:48 pm

Porsche had an early 911 body they hot dipped sitting outside at the factory unpainted for at least 20 years and it looked like new. Maybe it's still there.

Tue Dec 04, 2007 11:11 am

engineerscott wrote: Kombi wrote: Priming over zinc is not a problem... I've never considered zinc priming a whole panel, but I use a zinc primer as a weld through primer.

For a good weld you need clean steel, but using a zinc weld through primer allows a protection coat and still allows good penetration.

Although zinc plating may be a whole different game than a zinc primer...

Priming with a zinc rich primer and zinc plating bare metal are two different animals. They both use zinc to act as a sacrificial anode to chemically "tie up" corrosive elements that would otherwise bond with the iron in the steel to form iron oxide (rust) and other corrosive products.

Zinc rich primer is a primer which has very small particles of zinc suspended in an otherwise conventional primer. This offers improved protection over a conventional primer which does not offer this sacrificial anodic property.

Better than a zinc rich primer is actually applying a pure zinc coating directly onto the bare steel. This can be done either through hot dip galvanizing or through zinc electroplating (see my earlier post). Zinc coating of bare steel is superior in that both hot dip galvanizing and (to a somewhat lesser extent) zinc electroplating have a "self healing" property. If you scratch through the zinc coating down to bare steel the zinc surface crystals will actually migrate (i.e. grow) over time to cover the exposed metal. This effect is dependent on the thickness of the coating and the way it is applied. Hot dip galvanized coating will have the most pronounced self healing effect but moderately thick zinc electroplating will also exhibit this action, with the thicker the coating the more effective.

Scott
Some good info. At the factory it would be a straight process from one coating to the other, buit for someone at home or a shop, how is it to prime? Once youi got it back from the dipper or electroplater, would you light scuff 240-320 and prime with high build? Or is a tie coat of etch or something else required before priming?

Tue Dec 04, 2007 4:44 pm

Kombi wrote:
Some good info. At the factory it would be a straight process from one coating to the other, buit for someone at home or a shop, how is it to prime? Once youi got it back from the dipper or electroplater, would you light scuff 240-320 and prime with high build? Or is a tie coat of etch or something else required before priming?

If I were doing this my preference would be to wash the plated items with a mild phosphoric acid solution when they get back from the plater. You could very likely use Ospho (available at most hardware stores) for this. What this would do is "passivate" the zinc surface. Pure zinc is reactive (more reactive than iron which is why we plate stuff with it). If you wash the zinc plated surface with mild phosphoric acid you'll convert the zinc at the surface to zinc phosphate. Zinc phosphate is good for several reasons:

1.) It is fairly non-reactive and stable and will form a barrier coating, protecting the zinc (and steel) layers below.

2.) After phosphating the surface, the item can be put aside for priming and painting at a later date. Zinc oxide will not form and you will not need to do any further surface preparation before priming and painting (assuming you keep everything clean).

3.) Zinc phosphate is an excellent base for primer and offers superior adhesion properties. Any conventional automotive primer should adhere quit well to a zinc phosphate surface (better in fact than most primers will adhere to bare steel).

I have no idea what it would cost to do zinc electroplate on things the size of VW body panels but I am sure that the cost of doing a phosphate conversion wash after plating will be relatively cheap in comparison.

Scott

Tue Dec 04, 2007 5:55 pm

One method to prepare a galvanized surface is to simply wash it down with a vinager solution. Use the vinager on a clean rag and wipe it down.

Sun Dec 09, 2007 5:59 pm

Hey Gimmesomeshelter,

If you find someone that can do zinc electroplate on your body panels I'd be curious to know what the cost is for that process. If you don't mind, if you do find someone to do it how about dropping back into this thread and giving us an update.

Thanks,

Scott

Sun Dec 09, 2007 7:30 pm

Hello-

I'll be glad to. BTW, when I make this post I was actually thinking of suspension parts, but I guess it would also be a good idea for fenders, doors, hoods, and anything else that will fit into the electroplating vat.

Paul-