I've been using weld through primer in one form or another for 25+ years.

I started using the cold galvanizing high zinc epoxy paint, which is a great corrosion inhibiting coating, but a lousy weld through primer. It was one of the first products I found that claimed to be a weld through primer. You could get it in quarts or spray, but the spray is best used in a short time frame, as you'll probably have trouble from the spray can. The fumes from welding this is nasty and toxic, due to the zinc so respiratory protection is required. Of course any welding should be done with protection.

Then I found 3M which is better, but it too is best used within a short time frame or you'll have trouble with the spray can. New or old, this paint doesn't go on real smooth and tends to sputter and leave a mottled texture. It doesn't seem as nasty when burning it, but it's still not good.

The next product I tried was Transtar, which is much cheaper than 3M. It goes on a little smoother, but I had trouble with one out of three cans clogging and not spraying well.

Finally I got some U-Pol Weld #2, and to quote Snoop Dog, this is the "shizzle". Sprays out great leaves a nice smooth paint like finish, and doesn't clog. Seems to burn through easier too.

I do clean off as much paint as I can on the weld bead areas. With GT style plates, I use a dental tool and scratch off all the wtp in the plug weld holes. It makes starting the weld bead much easier and makes it easier to get a smooth clean weld.

Price wise I found a deal on the U-Pol on eBay, which was about $24 a can. Twice the price of the much cheaper Transtar, but worth every penny.

I had some older GT plates that had a black "high deposit" coating, which welds like crap. I ended up media blasting that stuff off because it's a total PITA.

This is just my own experience, your mileage may vary

Hey Perry,

Have you ever tried the Wurth zinc weld-thru primers?

https://www.wurthusa.com/Chemical-Product/P...Fl-Oz/p/0893109

https://www.wurthusa.com/Chemical-Product/P...Fl-Oz/p/0892200

Good, bad, ugly??

TIA
Tom
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I’ve used the Upol and thought it worked well also. Currently on the 911 I’m working on I’m using Eurospray copper weld-thru and it seems to weld easy enough and leaves a nice smooth finish. I agree on aoiding the zinc stuff. I already have to deal with enough zinc on the galvanneal parts.

Guy,

Since our 914 bodies & parts were never hot dipped in zinc based rust protection (as were 911/930/912E from 76 MY on), they have no real effective rust protection for the sheet metal.

Ergo, why it's attractive to use a zinc-rich primer as the sacrificial layer on top of the steel, in order to reduce or prevent future rust problems.

So air respirators may be a reasonable trade-off for better rust protection than just paint/primer & undercoating.

PS - Someone should "invent" a portable hot-dip tank for the early classic cars, that can go out to body shops like the mobile media-blast services, then it could be treated/dipped after all the welding is done!


Tom
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That's great tip. I don't know why that never occurred to me. I think we've all run the Gauntlet with crappy spray from different brands.

I purchased 2 separate spray cans of SEM weld thru primer, at like $18 a pop, and neither one of them would spray. So frustrating.. both were thoroughly shaken, both had been purchased before I needed and could not return because receipts lost (my local paint supplier sucks). I even tried new spray nozzles, nada. I highly suggest a brush on product if possible!

Our guy uses copper U-pol. I believe the cheaper stuff needs to be stored upside down for it to spray.

The modern version of a hot dip tank is called E-coat. It cost about $3K +\- we get it done on our more expensive builds. Got to add in $2K round trip to the dipper down south.

That's why I said "portable" or mobile Mark, so it's just the $3K & not $3+2 = $5K.

I've had really good luck with the Wurth rattle can stuff as far as no bad spray nozzles & even application, but I don't weld myself, & am using it as a protective anti-rust coating where I've wire wheeled off surface rust.

I did screw up on nozzle thru operator error, by not turning it upside down & spraying it clear between uses - 1 time, but was able to swap nozzles from another can.

I was just curious if the weld thru capability with the Wurth was "wurth it"??
... cuz it's more expensive than anything so far mentioned.

Also Eastwood has some zinc weld-thru primer(s), but I've not used them so far.


Tom
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So..... I know I'm a bit of a heretic but... I also loved the Upol #2 and thought it was the bomb and still kinda do. But after comparing the burn back I got with the Upol vs. Eastwood weld-thru vs. PPG 2k epoxy primer, I realized that no matter what I used, I wound up with about the same amount of bare metal where the paint burned off around the weld. The main difference was that the epoxy produced a lot of soot that the weld-thru paints didn't.

That sent me looking for test results to show that weld-thru primer actually results in better rust protection. You would think that manufacturers would run tests and use those positive results in marketing. I sure as would. After wasting way too much time looking, I found nothing which makes me very suspicious.

The only thing I found was a series of youtube vids by MrFireman where he tested a variety of weld-thru primers and epoxy by spraying, welding, leaving the parts outside to weather for several weeks, then pulling them open to see what happened. It's kind of a hodge podge and he didn't test every product with the same rigor, but everything he cut open all showed rust forming on the bare metal around the weld to different degrees. What did work was dribbling thinned down epoxy primer into the weld seem after it had cooled and then he got protection no matter what treatment he used before welding.

As much as I like Upol, the whole thing left me questioning what we are getting for our money.

If you use a sacrificial metal like zinc, it doesn’t have to completely cover the area. It’s proximity is enough to do the job.

Your talking about a tub that’s probably 20x10x8. Couple thousand pounds when filled with chemical. Same place has an acid dip tank to remove the paint, rust, etc. can’t exactly truck a couple thousand gallons of hazmat from state to state and even if you could. It’s going to cost a whole lot more than moving a car chassis.

I've been using the Eastwood weld thru primer with what I would say are decent results...interestingly enough, last weekend I sprayed a small area we were working on and was swarmed by literally hundreds of bee's. Not sure they loved or hated the smell but it was strange. My buddy is very allergic (epi pen allergic) and we both escaped unharmed...but it was pretty wild.

Actually Mark,

It's no where near as impossible nor expensive as you'd think.

That's about the size of a single TEU (20"' L x 10' W x 10' H) Shipping Container (most 18-wheelers are pulling 2 of twice that size containers 2-TEU 40' containers on dual trailers on the road), The single & double trailer tankers are pulling 70K - 90K lbs of fluids. Also at the more local truck size, there are a lot of mobile on-site trucks for services that mix cement/concrete, insulation, & other materials on 3-axle trucks which run around doing that size & weight of load all the time.

There are also other members on here who've posted that they had a mobile acid dip service come to the shop to dip their cars - so that side of it is already offered mobile.

The hot dip wouldn't be as haz-mat as the acid dip, & the current formulas which the auto manufacturers are using is far less toxic & relatively environmentally friendly.

But even if it were a haz-mat, then - yes - you can take it across state lines. I have several relatives who are haz-mat certified pro drivers who do just that.

The reality is that the businesses would probably be local & probably in major Metros where there is enough business to support them - there would be more business at price point without the extra $2K shipping.

Can it be done? Absolutely from a technical, logistical & legal standpoint.

Will it generate enough business to be a profitable venture? Well that's a subject for a more detailed business feasibility analysis than I'm going to do here to answer members questions!

I just floated the idea.

Cheers!
Tom
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I looked into getting the current chassis e-coated. It had already been dipped. After going 'round and 'round, it didn't seem like the way to go for a 914 chassis. Too many boxed in areas that would have the "Faraday effect"

Epoxy primer just works. I have also used Eastwoods high Zinc, and works just fine. Trick is all the places you want to weld, clear off the zinc. or epoxy. I have some old drill bits I grid flat to clean the plug areas with.

You will see MP&C post the above method. It works. Here is a good write up he did in this thread. . I have learned so much form his posts, and youtube channel.

I have a friend in town that restores and builds sunbeam tigers. When the cars are on the rotisserie he pours extra epoxy primer he has left in all the holes he can find, then spins it around for a bit to get the paint to flow around. Makes a mess, but things get covered and paint gets used instead of in the trash.

Weld thru primer just doesn't pencil out.. Steel melts at 2750 degrees so when welding no primer no matter what will withstand that. Its just good protection for the surrounding area..

I have tried it and it's fine but I think cold galv works just as good..

I think it’s like painting. Each guy has there own favorite meathods and products. If the final result is good, it doesn’t matter (much) how you get there.

Our cars rarely see rain anymore but storage is still an issue. I can barely open my garage since it’s cold insidevand the outside air is warm and humid. If the outside air mixes in, everything is damp in minutes.