I am about to have someone install some door frame stiffeners on my XJ. I just want to run this buy you folks to make sure I have the right idea. Once I prep all of the material with a sandblaster I am planning on priming *only* the backsides that will become inaccessible with U-Pol 0768 Copper WELD #2 weld thru primer. When I was originally talking to the guy who is going to install the new door stiffeners for me (he makes old school hot rods) he told me to not even use the weldable primer because it makes the welds look like ****. Well, I did a bunch of reading and learned that the proper way to apply the weld thru primer is to just paint the backside and that it is only for areas that become inaccessible after installation and it's not to paint the entire piece prior to welding.

What do you think? Do I have the right idea?

 

First, I'd like to commend you for doing your homework. When I did my stiffeners install I did not use any weld-thru primer and I now am seeing a large amount of rust propagate out from between the plating and unibody. Really wish I had used some. Along with that, I read up on weld-thru primers and the general consensus is that most of them suck. BUT, the U-Pol Copper WELD #2 you mentioned always was mentioned as an exclusion to that rule. I haven't used it, but I would definitely spend the money on it if I were to do it again.

As far as application, I can't answer that question. Applying to the back side and inaccessible areas sounds reasonable, but if you're leaving raw areas around the welds they will still start to rust. There really is no good way to get full coverage. This might be worth a call to U-Pol to ask their recommendations. I'd be interested to hear what they have to say. Maybe ask if your welder has any experience with that product in particular and, if not, if he would be willing to experiment with it a bit before tackling your project. You both could learn something. You could also ask him how he would prevent corrosion in a situation like this.

 

I've always used weld through primer and completely coat the entire piece and then wire brush the weld areas before welding. This method has given me good consistent welds.

 

haven't heard of u-pol, but if it's weldable, shouldn't need to worry. maybe the hotrod builder hasn't heard of, or tried that product?
up here, there is a new weldable paint that is getting all the raves, don't know if it's available in the U.S, it's called steel-it. it's 316L stainless steel paint. but it only comes in black and gray, i think. only two colours available.

 

I always used cold galvanizing spray paint from home depot with good results.

 

This is what I'm thinking of using for my rockers/boatsides...need to wear a respirator while welding it though I believe.

 

I did my floors, 2x6s, damn near most of my projects with it. Only time I used a respirator was when doing the floors in case some of that vintage seam sealer started to smoke. What'll get you is actual galvanized treated metal like street signs. The spray doesn't let off any smoke or odors

 

Zinc boils before steel melts so I think anything with zinc in it that is heated really hot might need respirator for complete safety. Unless you have a really good way to extract the fumes

 

We just keep the garage doors open. maybe a a fan on hot days.