Injecting well thru primer in between lap joints

[Schroeder]

What's the verdict on this today? I know it goes back and forth and there are different opinions. I am going to be welding a full rocker on this week. I was considering grinding off all the weld thru primer, welding two shiny surfaces together, and later going back and injecting the joint with urethane reduced spi epoxy. Or maybe I'd just slop it on with a brush. Currently medallion etching weld thru primer is on both mating surfaces that will be inaccessible after weld.

 

[MP&C]

I would recommend to get rid of the weld through primer, as it's name is misleading. My experience has been you don't want it anywhere near the weld puddle as it will outgas and balloon (contaminate) your weld where it becomes a porous mess. When we did some overlapping seams on Biederman front fenders, (see here) we had abraded bare metal that was welded together and brushed on SPI epoxy (no thinner, it's thin enough) directly against the flange, which wicks it between the two panels. We applied until it ran through, any areas that didn't run through got it from the opposite side. I think the SPI is going to give you better protection long term than the weld through. Epoxy vs. spray can, which is going to hold up longer?

 

[Schroeder]

I would recommend to get rid of the weld through primer, as it's name is misleading. My experience has been you don't want it anywhere near the weld puddle as it will outgas and balloon (contaminate) your weld where it becomes a porous mess. When we did some overlapping seams on Biederman front fenders, (see here) we had abraded bare metal that was welded together and brushed on SPI epoxy (no thinner, it's thin enough) directly against the flange, which wicks it between the two panels. We applied until it ran through, any areas that didn't run through got it from the opposite side. I think the SPI is going to give you better protection long term than the weld through. Epoxy vs. spray can, which is going to hold up longer?

That's what I'm thinking. I have seen this method pop up in different places on the internet, and it sounded appealing to me. Too bad I bought a bunch of weld thru for the project. Thanks for the input. Anyone else have thoughts?

 

[crashtech]

I'm only going to give the current I-CAR collision repair perspective, which may differ from the consensus here on the forum. If parts have no factory galvanizing or galvanneal, weld-through primer is indicated inside the pinchweld, inside the area of the HAZ (Heat Affected Zone). Ideally, the insides of the pinchwelds will have cured epoxy on them that is only removed right near the weld locations, where the epoxy would burn away. At those spots, a thin layer of weld-through primer is applied. After welding, the pinchweld may be saturated with epoxy primer to increase corrosion protection.

Some weld-through primers are worse than others when it comes to completing welds without small weld puddle explosions caused by expanding gases. In collision repair, we learn techniques to mitigate this because leaving the zinc coating , or re-applying it where it's been removed, is mandatory.

As far as I know, the only exception to this is Chrysler/Dodge/Jeep, which does not recommend the use of weld-through primer, but all their panels are zinc-coated from the factory. I need to review their stance on areas where the factory galvanizing has been compromised.

 

[Schroeder]

Thanks crashtech. Perfect response.

Maybe that's why all the Chrysler's are POS after 8 yes!!! Hahah

 

[Schroeder]

Double post alert!!

So I'll be doing some spraying tomorrow. It's gonna be on interior structural panels. All stuff that won't show, buts it's the stuff that rusts first (tail panel to trunk panel, inside door posts, etc. To be clear, spray this stuff with the cheap gun- NOT the iwata, right? And the metal temp has to be 65-70*. Right? Hit everything with waterborne wax and grease remover first. Right?

Another question that's heavily debated: a lot of this stuff is EDP coated. The panels are from goodmark, AMD, and I think one is dynacorn. The costing seems to scuff off with a surface prep disc, and I have yet to see any of the cost chipping. I'm good to spray right over it aren't I?

 

[Schroeder]

??

 

[elwood]

On restorations it is usually better to 80 grit and epoxy bare metal and go from there. Collision work is normally just scuffed, sealed with reduced epoxy then paint. Every situation is not always the same.

 

[El Toro]

I use the weld thru primer but don't like it. U-Pol zink . How about using glue made for rockers and aprons ? Made a small test on a lap joint that I bonded with glue been outside in weather for 3 years the bare metal has rusted but the lap joint has no rust. Just a thought??

 

[mitch_04]

??

Try wiping it off with lacquer thinner. If it stays, you are probably ok. If it comes off, sand it down.

If it was me I'd just strip it down so you KNOW it will stay. Either way, up to you.

 

[Schroeder]

Try wiping it off with lacquer thinner. If it stays, you are probably ok. If it comes off, sand it down.

If it was me I'd just strip it down so you KNOW it will stay. Either way, up to you.

Here's the predicament I'm in. I have a lot of stuff mocked up and I already have the weld through primer on it. Things are feeling good. I don't want to have to take stuff off and redo all this work if there is no real gain. Of course I'm not trying to take shortcuts I will do it in a heartbeat if it's the right thing to do I'm just not totally convinced and I don't want to be going backwards. You can see in these pictures the weld through primer on different lap joints that I have. I'm replacing almost every panel on this car. The sequence of events and what gets painted at what times and how many batches of paint I'm going to have to mix up is really confusing me when I'm starting from scratch it's hard to get that sequencing correct. I guess what I'd like to do is weld this full rocker on at this point because it's mocked up so well. At the same time I obviously don't want these lap joints to start rusting in 5 or 10 years. I will of course be ceiling them with seam sealer to though. What I plan on doing in a perfect world is welding this up, Spring epoxy on top of it afterwards, and then seam Sealing. My own Reserve is wondering if the weld through primer will ever flake off and thus the epoxy will too on top of it and that will leave Xposed metal but then again it'll still be under the seam sealer. What do you guys think? If I'm going to tear this apart for a little to no gain I'm not going to do it. if there are serious gains to be made in rust prevention by taking it apart, spraying everything off the car with epoxy, clearing areas where my welds will be, and putting it back on the car before weld I'll do it.


Edit: I just took paint thinner and rubbed it with an old sock on the EDP coating and also on some heavy areas where there is weld through primer. the EDP did not come off at all. the weld through primer had a little bit of red on my rag but very little. It could have been over spray from various applications. I'm leaning towards trusting it and just shooting epoxy over it.

Should areas such as the trunk that I plan on finishing in epoxy and not painting the base color of the car be sprayed over with epoxy used as a sealer as well?

 

[Schroeder]

I'm welding fellas! Anyone have input?

When assembling cars from scratch, do you guys put major panels on with just five to ten plug welds and spot welds and then come back later when you're sure that everything fits in lines up correctly?

Does anyone Stitch weld the floor Pantera car scene for added rigidity? I'm tempted to and had it that way on the original rocker panel. It made it very hard to get out, but I don't plan on ripping this car apart anytime soon or ever!