[Hot Rod Mike]

I have the doors apart on my 33 ford 3W, welding in new door skins. I know sandblasting followed by epoxy would provide excellent protection down the road, but setting up to spray in my garage (no paint booth) is a little difficult right now. Most of my major paint work is a year off or so.

I see ZRC, Crown (which Eastwood sells) & even Rustoleum make a cold galvanizing compound. Has anyone used this product before instead of epoxy coating for rust prevention? Did you top coat it afterward, or leave it alone ?

Thanks,
Mike

[MARTINSR]

NO, don't even think about using it for that purpose. "Cold galvanizing compound" is basically "Weld thru primer" a very rich in zinc paint. It has HOOOOOORRRRRRIIIBBBLE adhesion qualities.

Stick with your epoxy.

Brian

[Hot Rod Mike]

Brian,

OK, now I'm really confused since if this compound is similar to weld thru primer, why can't it be applied to properly prepared bare metal? I believe many use weld thru primer in areas that are inaccessible after welding. Can you elaborate?

Thanks (again),
Mike

[MARTINSR]

Weld thru primer is designed to be applied to hidden areas where metal is overlapping. It is NOT to be painted over, or primed over. You are told to wipe off (with lacquer thinner) ALL exposed weld thru prior to painting, priming or seam sealing.

I know from experiance, you can grind metal clean and apply it, after drying take your finger nail and scrap it right off!

Brian

[oldred]

MartinSr, I first started using the weld through coatings after learning about them here but I have used the cold galvanizing compounds for many years as a rust preventive for welds. They are similar but not exactly the same and cold galvanizing does work quite well however it CAN NOT be painted over, same with the weld through coatings. The cold galvanizing will work to protect the bare metal but I would only use it where it would be well hidden because it looks like crap.

Now about the weld through coatings, you mention that it will scrape off easily and I could be wrong but it seems to me that when heated by the weld it will adhere much better to the welded area than to metal that does not get hot. I noticed not long ago when I used this stuff (3M) on a trailer frame I was welding that the metal was well protected from rust where it got hot from the weld but the area that stayed cold had stated to rust after a couple of weeks, also the coating seemed to adhere much better in the heat affected area. The cold galvanizing compound is meant to be applied to cold metal and works quite well for that but it appears to me that the weld through needs to be heated in order to yield maximum protection. This is just an observation about the weld through needing to be heated and I may be completely off the mark but it sure seems to work that way to me. Either way though neither the weld through coating nor cold galvanizing should be painted.

[302 Z28]

Oldred is correct, cold galvanizing compound and weld through primer are two different things.

Vince

[MARTINSR]

I was told by the manufacturer of the Cold galvanizing compound was their "weld thru". I have used it, I have some in the garage. Though it has been so long I don't remember if it is "as bad" as weld thru when it comes to adhesion, but every other aspect of it was exactly the same, that I remember.

Red, as far as the "weld thru" being better once heated, yeah it could be. I do know that the recommendations for use has changed quite a bit from as recent as one year ago. Many automanucaturers don't even want it used on their cars. I think it is because the product has been WAY over used as well as incorrectly. I have seen guys grind off all the e-coat along the whole pinch weld on a quarter panel and then apply weld thru before putting the parts together and welding.

The most recent recommendations is to clean ONLY right at the spot weld that was removed, we are talking keeping the spot 3/8" or so large. Leaving the rest of the pinch weld alone and on the new panel put no weld thru at all leaving all the e-coat.

All I know is whether I am right, wrong, or anything in between "cold galvanizing" is NOT the product for this application.

Brian

[4 Jaw Chuck]

Never had much luck with it preventing corrosion, its too porous. Basically its zinc powder in a liquid solvent suspension. I had a couple of cans of the stuff and applied it to a trailer I had built, had corrosion in a few months from normal outdoor storage. Reapplied the stuff after prepping the areas in much heavier quantities (close to dripping and multiple coats) and still had corrosion a few months later.

I threw the rest away as it does not do what I had hoped it would and I do not recommend its use to prevent corrosion. Hot dip galvanizing is the only way to go IMHO. Maybe baking would melt the stuff and covert the coating into a non porous surface but sending it out for dipping is so much easier.

About the only use I can see, is to turn objects silver...for a short time anyway. Works well on wood!

[Hot Rod Mike]

Thanks to all for posting. I guess the jury is still out on this subject - at least in my opinion - so I'm better off using epoxy for sure & will change my plans for painting.

Thanks again,
Mike.

[oldred]

Hot Rod, the weld through works great for overlapping seams that have to be welded and will prevent rust between the overlapped pieces but it does not work very well as a rust preventive "paint" to cover open areas. I had exactly the same experience as 4Jaw when I tried to use it as a cold galvanizing paint and rust did start in a short time, however the welded areas stayed rust free which is why I came to the conclusion that the stuff needs to be heated to work. Cold galvanizing compound will work quite well on cold bare metal to prevent rust, much better than the weld through coating, but it sure would be ugly if it was used in an area that can be seen. I have seen the cold galvanizing protect welds on drain pipes for years even when lying outside in muddy conditions, far worse than anything a car is going to experience, but I just never found much of a use for it on cars because of the appearance.

[302 Z28]

Could be the differences in quality of product. I know the cold galvanizing stuff we used at work was made by CRC and it was some great stuff, holding up for a very long time in a chemical plant.

Vince

[oldred]

The cold galvanizing compounds we used were very heavy and had more of a thin paste-like consistency instead of the extremely thin stuff in spray cans. Probably the Zinc content is the same stuff but whatever it is mixed in must be quite a bit different. Although I suppose it would work good inside a door or some other place like that I would think there would be better products to use on body sheetmetal.

[scrimshaw]

Originally Posted by Hot Rod Mike

I have the doors apart on my 33 ford 3W, welding in new door skins. I know sandblasting followed by epoxy would provide excellent protection down the road, but setting up to spray in my garage (no paint booth) is a little difficult right now. Most of my major paint work is a year off or so.


Thanks,
Mike

Mike

There are other ways to apply the epoxy besides your spray equipment. Prevalve, roller or foambrush. The small high density white foam rollers you can buy in home depot leave a pretty good finish, it will require a little more sanding than if you spray it but might be worth it for your application.

[Hot Rod Mike]

Scrimshaw,

Thanks for the comments. I don't know why I didn't think of this before . This is exactly what I need to do so I can prep the inside of the doors, finish installation of the door skins & re-installon the inner door sections.

Obviously I've never done this before - do you thin the epoxy @ all ? Is this method covered w/the tech sheets on the product? Also, what is "prevalve"?

Thanks again,
Mike

[scrimshaw]

Originally Posted by Hot Rod Mike

Scrimshaw,

Obviously I've never done this before - do you thin the epoxy @ all ? Is this method covered w/the tech sheets on the product? Also, what is "prevalve"?

Thanks again,
Mike

With auto primer which I have only used two different types I have not found info in the tech sheets, but have talked with tech/supplier been told not to add thinner. I usually use US Paint or Interlux epoxy for fiberglass and this is not usually thinned either. I would advise talking to supplier/tech help if you are not sure.

Pre-valve is a small spray bottle, comes with compressed air cannister, just add the paint. Somewhat expensive but worth it for small jobs or touch-up, usually used on topcoat but can be used for epoxy primer if it is thin enough.