I'm starting to fix some rust through areas with welding in patch panels and when trying to get to bare metal I'm finding that some of the panels are all pitted with rust under the paint and bondo that some PO had applied. As I look at the total car, there are places where the paint is starting to peel and I'm sure it is from rust underneath. This is never going to be a show car, but a driver and a car to have fun with. At some point we will be repainting and I would like the paint to not rust through. As I'm working on sections I would like to do as good a job as I can. My sanding and grinding still leaves some pits of rust. Is there a way to get that out? I've used POR-15 on the frame, can I get most of the rust off and then give it a coat of POR-15 and still do body work over that?
I don't like using POR-15 under bodywork and paint on the outside of the car. It just seals the rust under a barrier, doesn't eliminate it. So, on the undercarriage, it doesn't show, and you can touch it up, if necessary. Though that stuff is usually so hard it doesn't chip easily. But on the outside, I've seen paint react with it, and have see how paint sometimes does not like to adhere to it. so I avoid using it on the exterior, under nice paint. I like to DA out the metal with 80 grit, then either scrub the metal with metal prep (Dupont 5717 is good) until all the dark spots in the pits is gone. Or, recently, I've been treating the metal with Picklex. It removes the rust much quicker than metalprep, and even takes off oils and contaminents. It works in about a minute or 2! I scrub it with a sctochbrite pad to help it work faster, and deeper in the pits, and wirebrushing helps if the pits are deep. you can sandblast the pits out, too, but be VERY careful of using a full size blaster. The small "spot blaster" works better and is safer. Just be sure your metal is sound...too many pits and it is weak, and may just blow away when you take the welder to it. Cut out all the weak stuff...and remember most times it is rusting from the backside, not the front. The damage is usually worse than you see!
i seen thread not long ago and picklex was mentioned , so this stuff really works that good? i saved the site to maybe purchase this product in the future .. thanks chopolds if im not mistaken it was you that mentioned this product..
I disagree about he POR15, it chemically changes the rust it comes in contact with. Though for a body panel I'd replace any weak spots and treat anything left with Ospho. Chopolds gives great advice,, we just disagree on what POR15 does....
Here is a thread that helped with rust prep/removal on my 55 Chevy. I had pitting and rust that would not cut with a D/A and the process in the attached thread worked well. http://www.hotrodders.com/forum/sec...al-revealed-55679.html?highlight=rust+removal
You could use phosphoric acid, its the active "secret" ingredient in por15. There is a chemical in the boating industry called "ospho" which I hear is excellent too. If your on a budget, Zep sells a concrete etcher that is like 80% phos acid. Nothing beats replacing the panel, though
This is a quote from POR-15's manufacturer's website. I don't like to argue, esp. with a knowledgable guy like zman, but even they do not claim to convert rust. It acts as a barrier, and is not degraded by moisture, so it lasts longer in harsh environments. I know it's a minor issue, in the grand scheme of things, but I can't help wanting to know HOW things work. It makes it easier to make choices in so many different situations.I use it (and similar products like Master Series Coatings) all the time, on underfloors, inside floors, trunks, behind panels to seal up welds, and protect from future rusting. but I'm just a bit uncomfortable putting an expensive paint job on top of it! "MANY PRODUCTS CLAIM TO STOP RUST; SOME ARE PAINTS, SOME ARE CONVERSION PRODUCTS, SOME ARE RUST TREATMENTS. NONE SEEM TO REALLY STOP RUST PERMANENTLY. WHY IS POR-15 DIFFERENT, AND WHY SHOULD I BELIEVE IT WILL WORK ANY BETTER? Rust is caused by moisture coming in contact with metal, which causes a chemical action called oxidation. All paints provide a measure of protection for a while, but since they are eventually softened and weakened by moisture, it is only a matter of time before moisture penetrates the painted surface and attacks the metal below. All of the so-called rust preventive paints on the market (except POR-15) are weakened by exposure to moisture. POR-15 is strengthened by exposure to moisture. Notice the hardness of the POR-15 coating. It doesn't chip, crack, or peel like ordinary paints do, and its hardness will resist the wear and tear of every day life. Rust conversion products claim to change the chemical nature of rust and convert it to a more stable element that won't rust again. History of the failure of these products is well do***ented; most simply don't work for more than a few months at best, and they are subject to the same chipping and cracking that occurs with ordinary rust coatings. POR-15 works because it chemically bonds to rusted metal and forms a rock- hard, non-porous coating that won't crack, chip, or peel. It keeps moisture away from metal with a coating that is strengthened by continued exposure to moisture. "
Sorry, Z, but POR-15 or any of these products don't change the rust, it encapsulates it. All of these products (I rep 2 of them) have a system which uses some type of phosphoric acid solution prior to treatment. That phosphoric acid does change the composition of the rust, but usually it is impossible to do fully and you then encapsulate the rust under the POR-15 (or whatever you're using). For the OP, you got good advice. Grind it off with 80 grits, mini-blast the pot holes, come back with epoxy primer then fill primer and finally paint. For more complete and fully accurate information go to www.autobodystore.com and check the forums there. Those guys will give you the whole story on prep.
Sand/media blasting first choice by far. Respirator and a d/a and some good old fashioned labor. I've found Ospho to work well, but it's a pain to clean up and get all the residue off...
Blast it and shoot the pitted area with feather fill or quick sand high build right a way after blast
My bad, but I swear when I first started using it that was what they claimed. Hmmmm... damn... Maybe it's like a waterproof watch, now they only call it water resistant? I must say though that I've used it a bunch and it works well in the right situation.
I do the same as Chopolds said....DA with 80 grit and metal prep. But I also sandblast when needed. Here is what Dupont 5717 and scotchbrite pads can do. Although it takes a lot of work. I will also spot blast some small areas that I couldn't get clean. I didn't want to sandblast the entire fender top and bottom and risk the chance of ruining it....its not really replaceable, it's a fender off of Marlene Deitrichs '29 Rolls. It's kinda hard to believe it's the same fender.
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