Re-painting & galvinising

[550Spyder]

Guys

My understanding is that post 76 all 911 cars were full body galvanised for rust protection (hot dipped).

I have seen quite a few cars for sale recently that have been re painted, and one in particular that was hand filed beck to bare metal (by a well respected shop). I know that when someone backed into the side of my 964 in NZ there was only one panel shop in the country (Owen Evans) that has the kit to repair and restore a factory spec galvanised protection as part of the repair (... And yes I took it to him to get it repaired).

My questions are

(1) is it more common here in Australia for panel shops to be able to re-galvanise the body before repainting?

(2) is buying a repainted car, that while looks superficially good in the short term, but is now missing its galvanising asking for trouble? and

(3) I don't really understand catholic protection, but does the original hot dipped galvanising coating that will still exist on the inside/underside of the panel still offer any protection or does it have to be both sides to act as some sort of barrier / shield?

Any experienced panel beaters out there with knowledge in this?

[Russ]

I think it's a bit of a gamble - anytime you rub back to bare metal you take the galvanising off and leave it open to reacting with any paint

 

I'm not sure anyone actually galvanises or repairs the gal (at least that I've talked to anyway)

 

I've been thinking about it for one day if I ever restore my car, wonder if anyone will do a full car in hot dip galvanising

[Tit]

Catholic protection.... Lol

[Caledonian]

My questions are 
(1) is it more common here in Australia for panel shops to be able to re-galvanise the body before repainting?
(2) is buying a repainted car, that while looks superficially good in the short term, but is now missing its galvanising asking for trouble? and
(3) I don't really understand catholic protection, but does the original hot dipped galvanising coating that will still exist on the inside/underside of the panel still offer any protection or does it have to be both sides to act as some sort of barrier / shield?

 

If you think of the galvanised items you see every day, fences, nuts bolts etc. generally ferrous items exposed to the elements and the galvanised coating protects the ferrous metal from oxidising. However, if the galvanised coating is damaged then the ferrous metal underneath is exposed and can/will oxidise (rust).

 

The paint applied to cars is fundamentally a protective coating (also looks good) if it gets damaged and the substrate (metal) is exposed to the elements it will rust, but if the metal underneath is galvanised there is another layer of protection.  As I recall this was one of the selling points of galvanised bodies. As for the inner panels, the galvanised coat does offer an added protection but it is not that flexible and panel seams/joints will flex can cause a crack into the galvanised coating and let moisture, again this can be the cause of rust in these areas.

 

In all probability, many Porsches would have had minor repairs to the bodywork carried out in the factory pre-paint and the galvanised coating would get damaged/removed in doing these repairs. From what i can recall from back in the day of being an "experienced panel beater" Audi and VW also had galvanised panels on some models and while there was a need for specific products to be used in the repair process, filler/primers etc, so they would stick to the substrate, but no re-application of a galvanised coatings was done. I think more problems would occur from not using the correct products on the galvanised areas more then not re-galvinising the damaged area. 

 

Refinishing technology has moved on leaps and bounds in the last 30 odd  years, so generally speaking a good quality paint job done today would be way better than the original from Porsche e.g resistance to chipping ,UV resistant, shine/lustre and finish etc. (finish can be debatable).

 

Bare metal re-paints sound like they are the only way to do the job correctly, this can be the case if the vehicle has been painted so many times there is simply too much product on the car or the previous paint is of poor condition/standard etc. there are many other reasons but in general in if the surface (and whats underneath it) to be painted is in good condition there should be no need to go back to bare metal.

 

You will get painters that will not do a job unless its bare metal (older cars of course) this can be simply to eliminate any potential risk of problems with the old paint. 

 

When welding on new panels a special "Zinc Primer" is used on the bare metal surfaces to be welded, i should point out that the cathodic primer that is on new panels (usually brown but can be grey or grey green also) has to be removed first. The "Zinc Primer " is electrically conductive to allow the panels to be welded and the heat on the weld melts the primer to protect the weld form moisture etc.

 

 

I've been in or connected to the motor vehicle repair industry for over 35 years and this is my version of the truth   you will find many others. I hope this helps but if you Google your questions you should find similar verified versions of the truth if you want more detail, but i hope this helps.

[550Spyder]

Caledonian.

Thanks for the overview. I had mistaken the galv for some sort of cathodic (not catholic - thanks autocorrect) sacrificial anode, rather than just another protective layer.

I appreciate you taking the time to educate.

[Russ]

Do some Porsches have sacrificial anodes between panels?

[Caledonian]

Do some Porsches have sacrificial anodes between panels?

Not that I'm aware of....