I do pretty much the same thing louver guy does, though the grinder I use has a 5/8-11 hub so I get 61-5001-8756-4. My old 3M guy says it functions about the same as 36 grit, though they don't publish that. As stated, it leaves a pretty decent surface finish, smoother than 36 though acts just as aggresively. I like to finish with 80 paper on a DA just to make sure it's even. I then give it a phosphoric acid wash to keep it from rusting while I work on it or something else. I'll post a picture below of the A coupe I've been doing lately, though the frame was acid washed a couple years ago, no rust even in that time. As for painting on top of phosphoric acid treated, any stories you hear might be the result of not doing it correctly and leaving residue behind. All paint companies (major ones anyway) market a "metal prep", pre-paint product, that is basically phosphoric acid with dye in it. Good primers will stick if you get it clean (which you should be doing no matter what you prefer to use).
x2 on the 3M Strip It pads Chip recommended. I use the little 3" ones on a pneumatic die grinder all the time to clean up sheet metal for welding. They are aggressive enough to grind through metal (with time of course) or soften up hard edges, but gentle enough to just strip a surface clean and smooth. They can and do come apart if they catch on an edge (which also severely shorten its lifespan), so stay away from edges and wear eye protection for sure. A variable speed grinder is the best bet. They don't need to spin fast to be effective.
Gl*** bead works great, but dont forget the hours of clean up time involved to get all the gl*** bead out of every nook and cranny of the entire car before you can go any further.
I had my 49 Cadi soda blasted and you're right it's totally clean, but if the cars not all blown apart and it's something you want to do at home to cut cost sanding it yourself is the way to go. I remember years ago it cost me $500 just to have a 31 Model A blasted. Thats not chump change these days.
For those of you using phosphoric acid, how much of a film does it leave behind, and do you have to scuff it again before you go to epoxy primer?
If I'm dealing with bare metal like pictured above I brush on the acid, let it work for a couple hours, then wash it off with water and dry it. That both neutralizes it and washes off the part that forms a film rather than iron phosphate. What you see in my pictures is the color of the iron phosphate. Depending on what kind of metal work was done I might go over it with 80 on the DA (to give it some "tooth") after doing a wash down with wax and grease remover, then wax and grease remover again before applying the epoxy. If the bare treated metal has been sitting for quite awhile, even though there may not be any visible rust (though oc***ionally there's a light amount where I didn't brush on enough acid the first time)I'll give it another acid wash to take care of any microscopic/very fine rust before going into the normal prep process just before priming. It works for me.
This is what I have done for lots of years. A lot of people feel funny about washing phosphate off with water. Its natural reaction to freak out over water and bare metal. The metal isnt bare, though. The water washes away the acid and other **** and leaves a nice coat of anti-rust!
The shop I work at media blasts every complete build we do. It isnt always a perfectly clean car when done. We use an industrial diesel compressor and medium aggressive media. It wont take off bondo if it is slathered on. And it blasts at 175psi. Not to mention that after our blaster has flipped the car on the rotissery a dozen times, vacuumed it out, blown it out and repeted, there is still a lot of grit in the car. And it only gets what you can get to. The only way to completely remove any and all rust from a car is to have it acid dipped, and thats a whole other different set of problems.
I'd guess that all those nooks and crannys are the sort of place water can get trapped when driving, or wet sanding, and where you can't really get paint to protect it. I'd also guess that an acid dip, followed by a water dip, followed by a careful drying and blowing out with air hose, would be the best way to get the car back to perfectly rust free condition. In a perfect world, of course....
That might be the case, but also consider this... If dipping is the only way to get into those nooks and crannies to get them clean, now you have to figure out a way to get back into there to cover them up. I don't have any experience in that area, so I can't really comment, just something to think about.
There is also an E coat dipping process where they dip the whole body in Primer to get into all those nook and Crannies.
Great info here. I have been just doing a little here and there on a VW over a period of a year and it seems the older spots with primer just start sprouting new rust again. So now I am in a vicious circle of never-ending preparation.
I've bought new parts that had that stuff on it, but never had to chance to actually see it applied. I wonder if it's beyond the cost of the hobbyist or not, then again I don't know anywhere around me that does it either. But now I'm curious... Anybody here ever actually do it? Maybe it's just a matter of it not being widely available?
I know of places that dip bodies in some sort of phosphate coating tank, whatever it is. They do it immediately after stripping and washing.
I'm doing a floorless '32 5W body/shell. Same size grinder, 11,000 RPM/minute. Do you think two of these would cut the mustard? At $100 a pop, I want to make sure I dont buy too many, or not enough...
I have been hearing about using charcoal as a blasting media. Anybody tried that? Supposed to be real good at getting stuff off and less damaging to the metal underneath.
I've done more than half of the Model A coupe exterior you'll see in my album with just one disc so far, so I expect to only use, at most, two discs for the complete exterior and door jams of the body shell, doors and deck lid. I got my discs from a guy on ebay, $5 for two plus $5 shipping, so basically $5 a piece. 11,000 would be too high a speed I think. I use one of my old variable speed buffers dialed down to about 1800 so as to not heat up the metal too much. I let the disc do the work so little to no pressure other than the weight of the buffer. When the disc is fresh and has a square edge it will get into the crevices of the reveals, but as it wears the reveals won't get done without resorting to other methods. Either a heat gun and putty knife or aircraft paint remover will finish off those very thin lines of remaining paint.
I was wondering about that! Thanks for the advice! I'm going into evilbay to find those wheels. $200 is a tad pricey, but still cheaper than other options.
The Jalopy Journal
