Weld thru primer

[robotman]

Can i weld thru two mating pieces of metal that have been primered or have a coating of purple power de-ruster? I did not get a clear answer on the technical forum.

[70SWT]

The advice I have gotten is that it is best to avoid the stuff, i.e., grind it off of any surfaces you plan to weld together. It is OK to leave it on the inner aspects of rocker panels etc or other places where actual welding will not take place.

I understand that for stick welding of thick metal, you can have this stuff or even rust on it and it won't matter, you'll burn it off. But for thin automotive sheetmetal you want to have clean surfaces, since things need to be optimal for the thin metal to bond together with max strength.

Just one jackleg's opinion...

[Rjackel944]

why not just sand it off? Welding on metal with any kind of primer/paint coating can create hazardous gasses.
Also, it can effect the arc and or gas shielding especially with GMAW (mig) and you could possible end up with porosity or other weld defects.

long story short, only weld on clean metal

GL,
Ryan

[RichF]

What about the bare surface between the two panels you weld? Wouldn't those places be prone to rust? Or is seam sealer the fix for that problem?

[robotman]

Ok, I am going to keep the area clean where all the spot welds are and then get in there with a wand sprayer with deruster under neath and then prime and paint.
Seam sealer inside where exposed.
Man this is a ton of work.

[perrygrandprix]

Hi Robotman

I have spent most of my life in the motor body repair industry and can tell you that welding through ordinary surface primers is a waste of time.

If you are really concerned about metal joins being bare i.e between two seams, you can in Australia for example purchase specific priming material/coatings for welding through that you brush on the cleaned/ground surface before welding. One such brand available here in Australia ïs branded "Volvo"on the label. I don't know if it is made by Volvo or just by chance carries the name.

I have watched many car repairs being done where two pieces of sheet are first disc sanded to remove paint coatings then welded together with either oxy,mig or spot welding (Spot or fuse welding probably has the cleanest results).

The problem with not using a weld through primer is that some time down the road when sweating or moisture occurs it causes the cleaned/ground metal surfaces to rust.

An example would be a turret replacement due to hail stone damage and all joins are cleaned of paint then welded. Some years later the seams start to swell and burst apart with rust.

Most general motor body repairers don't concern themselves with this aspect because it takes many years to come to the surface or show. By the time it is painted and reassembled everybody forgets.

Do ask around the bigger and more reputable panel shop material suppliers. I am sure in a country like the US similar products would also be available. You could perhaps ask welding equipment suppliers also.

cheers
perrygrandprix

[hemeoncdoc]

One possibility would be to electrocoat (e-coat) the entire unibody after all welding and sheet metal work has been completed. It requires that the entire chassis be stripped of all paint/undercoating, but must be the best way to seal all chassis metal surfaces, inside and out. The body is dipped into the solution, it electrostatically coats all surfaces - unlike powderpainting it coats even inside of channels, etc. It is then baked like powderpaint. E-coat is on all of the new cars and new OEM sheet metal parts.
My 68 911 is headed for the e-coat, after a bake-off and light media blasting.

[robotman]

Thanks for the info, i ended up welding the seat panel in and then rust proofing underneath with a chemical sprayer to get into hard to get places.
Old metal is a major pain to weld, very diffirent than new steel.

[Griffinroydonal]

We use flap sanding wheels on a 6'' grinder to prep all parts to be welded. This makes it easier to start an arch and keep the heat even on both pieces of metal. The final weld has a smooth bead and then we use a wire wheel to remove slag and prime. This looks very good under paint and has no later rust issues.

[robotman]

Thank you for the info

[abisel]

Originally Posted by hemeoncdoc

My 68 911 is headed for the e-coat, after a bake-off and light media blasting.

Where will you be sending your '68 to get e-coated?

I plan to do the same on my '73 RSR project and I only know of 3 places.

One of them will only do it if they are already working on your car ECoat Electrocoating Information.

The second uses iron phosplate of which I don't want (redi-coat I think).

and the third's tanks would require the body to be turned on it's side. Systems Electro Coating | Home

What have you found?

[hemeoncdoc]

Talk to Aaron at Zuffenhaus in Charlotte. They do a great job, take care of all logistics, to include putting the car on its side (tank is 4' wide). Good luck!

[abisel]

Originally Posted by hemeoncdoc

Talk to Aaron at Zuffenhaus in Charlotte. They do a great job, take care of all logistics, to include putting the car on its side (tank is 4' wide). Good luck!

Thanks,

I will give them a call.

[alballs537]

Hi I did not read all the comments but the first couple really did not answer question. Any good auto body paint shop store sells or can get a primer made for that it is called weld through primer so you prime everything that cannot be seen after welding the you are guaranteed you new metal is primed let me know I do not have name brand in front of me but will get it if you need. Should be easy to get just have to find place to buy it. I am restoring my 68 912 and that is all I use on metal that needs to be welded and not seen. I think it was 15.00 a can pricey but well worth the price for what it does. Thanks have a great day

[abisel]

I have tried 3M, Rustolem, and lately UPOL. I found UPOL to be much better in both spot welding and MIG. I got it at my local auto paint supply. The had to order it, and it only cost $8.

The spot welding went has normal, no indications that there was no electrical contact between the two sheet metal pieces. As for the MIG welding, I did not apply the weld thru beyond the weld seam, so the MIG welding went as normal too.

[962porsche]

weldable primes are made for the MATTING of the 2 or 3 inner surfaces . like the pinch welds on rockers and door jams . it is only needed were panels over lap and you can't get an e-primer on them afterwords . its a zinc based primer so as you weld it will burn away very ez but also the zinc will surround and will attract to the high heat of the weld . your wasting your money and time putting weld primers on some thing you can get to after your project id all welded together . in my shop we use brushable weld primes most of the time its more cost affective and much easier to use . becouse of no masking off the main body of the car . when it comes to weld primers less is better ! all you need is to get the bare mettal covered ! using less will give you better welds with better and easier penetration of your welds .

[merbesfield]

abisel, So to clarify, you like the the U-POL rattle can welding primer fro seams and spot welds? You have found that is does not impede the quality of your spot welds and your welder strikes good contact with no splattering and popping? I am not talking about using a spot welder gun, I am talking about welding spot welds using a mig welder and welding drilled out old spot welds when making a repair etc.

[abisel]

merbesfield,

When I welded with the MIG, I did not have any popping or spattering. However, I did not have U-Pol beyond the edge either. There was a couple holes that I filled with MIG, but I first removed the U-Pol with lacqur thinner. So I can't say that you can get a good weld right onto the U-Pol. As 962porsche says, the weld through primer is good for mating two pieces as I have done here.

As for the resistive spot welder, it worked like a charm. The U-Pol provided good conductivity for the spot nuggets. And when it melts from the heat, it flows right back around the weld nugget.

[merbesfield]

I ordered two cans of U-Pol. I found it on the net for $5.60 a can. Of course shipping was that much as well, but still half of what others were selling it for.

[abisel]

merbesfield,

Here is a link where I used the weld thru again for mating two pieces together. Nothing beyond the outline of the reinforcement sheetmetal was coated with the weld thru.

Post pics of 1973 Carrera RSR replicas here...