Media Blasting

[Donny]

Folks, I've done a lot of cars with my Media Blasting apparatus. Today, I was finishing up a 54 Chevy truck. It had been painted sometime since leaving the factory with a nice Blue color, which actually looked pretty good! However, when I started peeling off the paint with my 20 PSI / 200 CFM Plastic Media Blasting system there was NO factory paint, nor primer. Some bozo years ago sanded it off, and put this Blue stuff on. What is problematic is the metal had flash rust on it, under the paint! My soft media does not cut into that too well, I added a bit of Alum Oxide to cut into it a bit to take it down to bare metal, it came out really good.

My point is, folks you HAVE to have your cars Media Blasted, only this way can you uncover the ills of previous 'expert' painters, body men, etc.

After tending to this Chevy, I went to my Satellite to blast the inner front fenders (see my pics in "What's Everyone Working On" thread). Here is where I show my ass; years ago, I bought into that hype of using POR-15. What utter shit this stuff is. I lathered it on thinking I could 'preserve', and encapsulate the metal in a preserved form. There is nothing further from the truth. I have only a little bit of this horrid shit to Media Blast off my Satellite then it's just paint(s). POR-15 is only good for ocean going vessels that are fighting rust all the time, not our nice MOPARS!

One word of advice; don't sandblast! It has too high a pressure, and, often we want to be backyard experts (I used to be this way) and, it takes too long, I remember taking all day to sand blast the inside of a hood, that was junk, I wasted 8 hrs just on a hood, the inside! Today, I do a whole car in 8 hrs, with soft media, low pressure, and expert handling!

Oh yeah, don't be afraid to take it down to bare metal, this is the ONLY way you can see what you have to start your build-up on your (our) dream cars!

www.drblast.com

[5.7 hemi]

Good advice!!!!!!!!!!!!!

[Donny]

Thanks 5.7!

[Meep-Meep]

Interesting info, but more data would be nice. How was the metal cleaned and treated on your car prior to application? The POR people say the metal has to be treated properly with the acid stuff so it adheres. I followed the instructions to the letter and used it on my suspension parts and seems OK but only time and use will tell.

Media blasting is great stuff!! I had a 68 Mustang GT done about 15 yrs ago and it came out like factory new metal, except where the bad parts were

I have also used a 3500 PSI pressure washer with a sand attachment to strip an engine compartment. It was like painting it silver!! Nothing stood a chance and I was done in short order but the driveway looked like a beach. Oh well, it's just sand.

[daredevil]

whats a sand atachment ?

[Donny]

Well, POR 15 is a good product, and, if you like it, then great! Since I do Media Blasting, I don't need to engage is covering the rust/crud and encapsulating it, I just blast it.

[Meep-Meep]

I can't say one way or another regarding the durability of POR 15. All I know is it went on well and seems to stick. Get back to me after I get the car running and logged 50 K miles.

Best I can figure the sand attachment was a siphon thing that went on the end of the pressure washer nozzle. Stick the hose in a bag of sand, pull the trigger and hang on! Your pressure washer is now a wet sand blaster!!

[detmatt1]

That is some good info in this thread, Thanks

[scotts74birds]

Great thread, but if go the route of having the shell media blasted before I do the metalwork, how do I keep it from rusting in the meantime? I've seen the epoxy primers, and people recommended using an etching primer to cover it during the bodywork, before paint. What do you folks recommend? My RR has some issues but the underneath is solid. Matter of fact, I almost think the bottom has been Rhino-lined! Is that even practical? I live 3 miles from the nearest paved road so I actually think its great.... in theory? What do you all think, thanks Scotty

[Donny]

You can have it Plastic Media Blasted and work the bare metal for months as long as you are in a dry garage. I know, last year Oct I did my Satellite qtr panel (3 minutes), and it's still bare metal, with no rust, and I had a bit of crushed glass in the mix to 'cut' a bit better and give a good profile for primer to adhere to.

Rhino lining is very difficult to remove. Your best thing to do is put the car on a Rotisserie, but as soon as you get it on, install the frame stiffening devices so you won't have any sag or give while the car is up there for months.

I have done alot of painting my own stuff (don't do for customers) and on bare metal I use a self etching primer, then Urethane Primer, then a build primer as needed, then maybe some more Urethane depending on how much you sanded off...then base coat.

Good luck!

[69 Runner]

Yup. Unlike sanding, media blasting won't hurt the metal's surface, and therefore the original zinc (or whatever) rustproofing from the factory

[scotts74birds]

HaHa! yeah, factory rust-proofing, you're funny dude! Just kidding, I've watched your posts and you are some of the sharpest folks I've met on these forums. Thank you both for your advice. This is a learning experience for me and I try to read as much as possible before asking a question, or acting. Speaking of frame stiffening, I also need to replace the roof [rollover, that's why it was so cheap!]. Any advice on tying the unibody together before cutting, or should I make that another thread? Thanx, Scotty

[gregs70]

Donny, I lived in Texas for 20 years then moved back to Ohio. Bare metal doesn't last long at all in more humid areas like Cleveland.

[B392Hemi]

I have used OSPHO with pretty good results over the years. It is a good "keeper" of the metal until the body work is done, and I have always DA'd the bare metal (that had been OSPHO'd) with 80 or 100 grit before I put any substrate down. I've done several cars over several years, and have not had rust come back. AND< I live 2 blocks from the Pacific Ocean..!

[scotts74birds]

Thank you for that tip, I learn from asking and watching. I'm not in the trade, so what is substrate, you mean filler or..? I thought that I read that certain types of blasting can leave a residue. I.E.soda, it can protect the metal, but it can hinder paint adhesion if not removed properly before application of other products. I'm learning that paint and body is a skilled trade that is overlooked. I am an electrician, and I know the work that goes into learning your trade. You body guys have a wealth of knowledge that you only learn by time and trial. Thank you for sharing some of it.

[Meep-Meep]

If you treat bare steel with phosphoric acid (metal prep or similar) it will slow down the corrosion process but not stop it. I think the etching primer has a similar effect. What the acid does is work with the free iron in the steel to grow a zinc phosphate layer on the surface so the paint adheres better. Note the green factory primer on our MoPars was usually zinc chromate.

Regarding rust hole repairs. Where you cut out a section and weld in a new one, keep in mind the steel must be sealed from oxygen ON BOTH SIDES OF THE REPAIR or you will have another hole eventually - hence the creation of the term "rust never sleeps".

[Donny]

I was Media Blasting a customers car parts last night; 64 Nova/Chevy II, man, one of his fenders was junk, I didn't blast it as it would be wasting his money, it was too far gone, client said ok, I will buy a new one. But, the other fender appeared good, but rather heavy before blasting. I swear, this thing had about 15 lbs of filler in it! No joke, I have pics and will post them here in a bit...when done, it was super light.

This is one area I've not thought of too much; the weight Plastic Body Fillers, or whatever kinds of fillers occupy our cars! I do recall in the 70s using Bondo was a thing to do, at least this was the impression I had back then being a kid just maintaining a wide-eye/amazement to this trade/hobby.

Something to consider...

[Donny]

Here's some pics: See how thick this filler is?



[IMG][/IMG]

[Donny]

Again and again, and last night was no different, I was 'surging' on the 31 Model A to get it done, (been putting it off for nearly 2 weeks now with school and family coming in from out of town) but last night I got to my 95% done mark. When I get there, I shut down, regroup, sweep up, get some rest, and hit it later to finish it up. Well, the trunk lid on this 31 was filled, I mean filled with 25 lbs of bondo, in one place it was 3/4 inch thick! No joke. And, wearing that crap down takes a LOT of time. On pieces like that I have to charge more...but the reason I post this is b/c the observations I make when peeling this stuff off. I wonder, when, between 1931 and now was it considered De Jure to lather this crap on like this? With all the sanding to make it smooth, why not just re-skin it? I remember in the 70s Bondo was all the rage! You don't know how many cars I get with tons of this stuff on it, often covering rust up. I have a mini camera I think I will mount to my hood and will get some birds eye views and post 'em on youtube under mr954. What you all think, I think that would be a cool video to watch?

[69 Runner]

I watch these car building shows all the time and am amazed at the amount of bondo they use. "SKIM cotes" they say. Except the entire car is "skimmed".