How to remove Galvanizing on Auto Sheetmetal?

[Tigers]

I'm replacing body panels on a car which has galvanized coating on the sheet metal from factory. I'm having a difficult time finding the right method to remove the coating. Twisted cable wire wheel on an angle grinder is ovaling the spot welds which were drilled out and doesn't seem to remove all of the coating. I tried vinegar which does nothing and phosphoric acid which bubbles a little but after several re-applications doesn't appear to remove the coating either. Should I just brush on muriatic acid or is there another way?

Thanks

[mla2ofus]

A fine grit flap disc will remove it without removing much iron.
Mike

[WNY_TomB]

I'm replacing body panels on a car which has galvanized coating on the sheet metal from factory. I'm having a difficult time finding the right method to remove the coating. Twisted cable wire wheel on an angle grinder is ovaling the spot welds which were drilled out and doesn't seem to remove all of the coating. I tried vinegar which does nothing and phosphoric acid which bubbles a little but after several re-applications doesn't appear to remove the coating either. Should I just brush on muriatic acid or is there another way?

Thanks

.
why remove zinc coating ?? silicon bronze "everdur" is used to tig and mig galvanized steel as it doesnt mind a little zinc mixed in and does the least damage to the zinc at the weld area. also silicon bronze melts before steel. in theory you are not melting any steel but are brazing it. been used by tin knockers making galvanized ductwork for a long time. in the old days they did not even used a tig torch but used a single carbon electrode with a dc welder.

[madmax718]

err.... Ok, so there's a lot of potential for... variations here.

On new panels, if they didn't already come with the spot weld holes, you should be using a punch to do it. Its safer and doesnt leave as sharp an edge on the back side
Its generally not necessary to remove any part of the coating. Its what protects the metal, especially at the weld area. Theres enough of an exposed lip from the punch. The vapors are what will get you so use proper precaution

2. 3m roloc discs are the way to go. Pretty much ANYTHING on an angle grinder is over kill for panel work. ( i say pretty much, but there are exceptions to statement). Angle die grinder with roloc adapter is how I was taught and how I learned. Works like a champ, and nearly impossible to gouge the metal as you described.

If you do decide to remove the galvanizing, you should at least replace it with weld through primer.

[Bonzoo]

Galv auto body ? I'm old and don't work on things less than about 30 years... Get after it with sil-bronze I suppose. That would be my first shot.

[madmax718]

Most cars after 1987 came with galvanized bodies and panels. Most panels were spot welded after that, but they just used a spot welder, not mig. Mig is the approved way for most after factory crash and rust repairs. This is why you see a lot more cars made after 1987 than before 1987. (or roughly there abouts). You might also remember seeing a bunch of GM cars that look like the paint was peeled off, but no rust. That was late 80's early 90's GM paint tech. they had issues with adhesion between the paint and the factory galvanizing.

This article mentions the problem

https://www.washingtonpost.com/archi...=.9b584eba7d4f

oh, and 1987 is 30 years already. lol. You also wouldnt be very safe with sil bronz as it isnt an approved repair for unibody cars.

[Bonzoo]

Most cars after 1987 came with galvanized bodies and panels. Most panels were spot welded after that, but they just used a spot welder, not mig. Mig is the approved way for most after factory crash and rust repairs. This is why you see a lot more cars made after 1987 than before 1987. (or roughly there abouts). You might also remember seeing a bunch of GM cars that look like the paint was peeled off, but no rust. That was late 80's early 90's GM paint tech. they had issues with adhesion between the paint and the factory galvanizing.

This article mentions the problem

https://www.washingtonpost.com/archi...=.9b584eba7d4f

oh, and 1987 is 30 years already. lol. You also wouldnt be very safe with sil bronz as it isnt an approved repair for unibody cars.

Thanks for the reminder. I bought a brand new 1999 GMC van and the paint peeled off the roof in a couple of months. GARBAGE.
Galv is garbage for most everything. I refuse to build with it.

[Tigers]

I'll give the roloc discs a try since it sounds like abrasive is the way to go.

I'm using TIG to join the panels since that's what I've got. Weld through primer will mess with the arc quality. Any suggestions how to protect the metal inside the joint?

[duramax-rob]

just as a note to the gm, ford, chrysler paint was that all the colors effected were clear coat colors. the factory paint manufactures didn't put enough uv protector in the clear and and the sunlight (uv) would go thru the clearcoat and the color. the color was so thin because of EPA regulations. the uv's would then attack the primer which would then chaulk up and and cause the color and clear coat to lift. you never saw and rusty cars, just cars running around with gray primer and peeling paint. after the sun and years of this, the primer gradually would come or wear off to the metal, then it would rust.

as far as removing galvanizing, 80 grit on a grinder or rolock disk worked for us.

[131re]

You also wouldnt be very safe with sil bronz as it isnt an approved repair for unibody cars.

You might want to read up on UHSS and silicone bronze
http://www.repairerdrivennews.com/20...ght-demand-it/
http://www.bodyshopbusiness.com/mig-...rning-process/