Most likely Tnemec, which is great stuff for bridges and water tanks, very expensive, and lasts for decades. But I wouldn't use it to paint a car. Typical coatings are very thick in that industry, and sags/runs/etc. don't matter.
TNEMEC.com

 

I understood exactly what Scott was saying I was going to post earlier but didn't want to dodge any sarcasm or sound like i was jumping on the wagon. Most everyone uses PoR 15 for their frames where you may not get all the rust off but few stray from the traditional epoxy over bare metal and then a more higher build primer before top coat ( proven automotive technique ) The pic of the peeling fender made me think the same.If it is holding up after 70 years it will hold another 70. Most all our problem areas is where mud layed.

 

I have a buddy who used to swear by POR-15 but after having it fail (delamination mostly) in various areas of his truck he has switched to KBS Rust Seal. I have used KBS for years and have never had any problems with it at all...well short of trying to get it off my skin! Don't want to beat a dead horse but I have been doing paint and body work for some 50 years now and would never consider using anything other than a quality DTM (direct to metal) primer on bare sheet metal. Good luck with your project...

 

 

 

 

Ha ha - I only wish I knew as much as you have forgotten about body work Scott!!

 

Thanks Jerry for the tip about the degreaser. If it was so critical though the manufacturer should really dilute it for you, I have tried their metal prep and didn't think it did much at all. Seems to me that it is acting like an etch primer so where the surface is too smooth you can still have problems with peeling. I would use POR for brake drums or my wheelbarrow frame but not on large surfaces areas or anywhere there is new or shiny metal.

 

For those that have been there. Ill be removing the bed to replace it in a month or so and my BIL thinks he can get us a small sandblaster to take care of most of the rust on the frame. If one has it down to nice clean metal what is the best option Prime and paint with regular epoxy paint?

 

 

I blasted my frame to bare metal, including getting all of the rust out of the pits. I just used epoxy after that.

Given that POR 15 may not stick well to clean bare steel, I would strongly advise against it. My research impressed upon me just how strong, tough, durable, and sticky the epoxy primer is that I personally don't believe that POR 15 is even close.

Just my $.02.

John

 

I always learned that you must prime bare metal first.

 

I've seen complaints like this, regarding POR, for a number of years. Considering my massive CRS affliction it seems to me most, but not all, of the problems occurred when used on sheet metal or overly-prepared metal. We use the stuff on fire trucks all the time and have little to no issues. Basically we knock off the loose stuff (flaking rust/paint), spray what remains with brake clean and wipe off with a shop rag. Then use a cheap foam brush to slob it on, brushing it out to a thin coat. Most of the apparatus around here will be in service for 15 - 20 years and it will still be in place unless it's been physically damaged. Maybe multiple layers aren't a good idea? Maybe thinner, more flexible steel breaks the bond as it shrinks/stretches/flexes? Maybe spraying vs. brush? We also only use the little 4 oz. cans to control waste - once you open it there's no going back to the same product quality, even if you can get the lid back off. LOL. I'm more of a mind to not use it on a large scale since it's like epoxy - if the surface fractures it will allow moisture behind it, trapping it between the metal and coating, making the problem worse. For under-car protection I'd be looking for something that doesn't completely cure like heavy wax-based or rubbery/asphalt type products. Think: self-healing. Personally, I would never recommend POR for a base/paint primer, but I'm no expert. Just random thoughts...

 

I prefer and use the little cans too. But the bigger cans are cheaper in the long run. You can keep it usable longer by placing a sheet of shrink/cling wrap over the top of the open can. Then push it down until it touches the surface of the paint. This forces the air/moisture out of the can. Make sure the sheet is big enough to go over the edges of the can. Then put the lid back on the can and store it in a refrigerator ( not one with food in it ) . This keeps all the paint usable except for a skim layer on the surface of the paint. That greatly increases the shelf life of a larger open can. And the cling wrap also makes it so the lid doesn't get glued to the can by the paint.

Do not use any kind of rubber/asphalt type of undercoating. Some of the rustiest vehicles I've ever owned were undercoated. Including a poor 56 F250. Huge sections of the floors and fenders were missing. With all that was left was rubber undercoating. It held moisture against the metal and rotted it away. What I've found works the best is a oil mixture that you coat the under side of the vehicle with. That's where the guys in the northeast and Canada have it right. Just recoat the underside every fall. It's a mess when you need to work on things but it drastically cuts down/stops the rust.

 

POR15 is made to go over firm RUST!
NOT sandblasted metal of clean metal.
I had some POR left over and seen my rusty trailer sitting over in the field looking very sad.
I took a roller and without even taking the dust off of it, I painted the whole thing.
years later it still had no flaking or rust showing, although it did turn flat and lost its shine.

Remember rule number one! Use it over rust!