Plastic Media Blasting?

Hey everybody, I hope someone can help me out with my newest project, a 1935 Ford pickup.
I'm getting ready to start on the body work, and ruled out acid dipping and sandblasting. I've been reading what I can find on plastic media blasting and it seems like it would work for me.
Two problems, nothing I've read details how well or if it removes rust, and I can't find anybody locally that advertises this service.
I'm in the N. Miami, Florida area, any suggestions or ideas would be greatly appreciated.

Thanks - Karl.

I've used media blasting on a few projects. It is okay, but if you can find someone who does walnut shell blasting, it's cheaper, and just as good.

Sandblasting would be fine, too, IF you use someone who does vintage cars often, so they know how to avoid warping the tin.

I think I've pretty much ruled out sandblasting, old metal is hard enough for me to weld without it being made even thinner.
I'd forgotten about walnut shell blasting, there used to be a guy out of Ft. Lauderdale that did it, but he had a truck mounted portable unit that wont do a body.
Any body know someone in the Miami area that does walnut shell blasting?
Thanks - Karl.

Plastic media blasting has almost no effect on rust at all. Does a heck of a job removing paint and "bondo". Gets into every nook and cranny and will keep coming out over time. The last car I did just kept weeping tiny pieces of the media no matter how many times I vacuumed, blew it out, or tried any other way to get into those hidden places.

Like HRP says, make sure the operator has lots of experience..............whichever material is used. In the wrong hands they can all do damage. If you do go with the plastic media, just plan on dealing with the rust by topical chemical rust removal, typically a phosphoric acid solution that is marketed under a lot of different names. And then some mechanical means such as "hamburger" wheel, or 3M conditioner wheels (similar to scotchbrite) It's more work for you, but you can control it better.

Have it chemically stripped.....

We had a 66 F40 Landcruiser dunked in a tank two years ago and we are sold on the process. The dunk removed rust, paint and just about everything else BUT it did not remove metal. After they dunk it, they wash it really good and then spray on a protective coating (phosphate?). It has been sitting in our shop for two years with no further protection and NO surface rust (results in Florida slightly different than Arizona). Anyway, the body guys LOVE it since they have a perfect metal starting point and no abrasives to blow out of seams, etc. The only risk is a poor rinsing after the dunk.....poor workmanship at the stripper is what gave the process a bad name......

It only cost $1500 to have the thing done....much cheaper than a drum of elbow grease.

I had originally considered that, but everything i read said that there were eventual problems with acid "leaching" out later on. I guess that goes back to what you said about the workmanship of whoever does that.
I thought that dipping also removed metal? Isn't that what they did on the "lightweight" racers of the 60's and 70's to remove metal and make them lighter?
It's definitely Phosphorous in some form or other that they use to protect the metal, that's where you hear something like "body in white" due to the white color of the phosphorous.
Well, thanks for the replies.
Karl.

the classic "acid dipping" was intended to remove metal. The "old wives tale" was that they left the object in the tank for a longer period of time to reduce the thickness. Actually, it was probably a more acidic solution. When we had the Landcruiser dunked, they were doing some ancient Ferrari aluminum block....
if it was a metal removal process, they wouldnt have risked the block.

Also, regarding leaching from seams, we havent seen any indication of anything such. We have taken a blow gun to the seams and in the sheet metal bracing and nothing comes out. The only thing that didnt come out was a couple of places where bondo was in the dent puller holes and that popped out with a knife.

For the plastic media, look at Randy's web page
http://www.hotrodscustomstuff.com/prostrip.html
that has some pics

This is one of the few times I may be in disagreement with my buddy Mike.

I've known two cars that were dipped and later had a problem with paint "failure". One took about 3 years, the other around 5 or so. I'm not convinced it was the acid solution coming out after that much time. My guess was that the acid kept working in the seams where it wasn't flushed out properly. This allowed corrosion to form from the inside out. Vulnerable spots are anywhere two panels are spot welded together, e.g. firewall to cowl, wheelhouse to quarterpanel, quarterpanel to rocker, and so forth. I suppose if the acid were neutralized thoroughly, and then some anti-corrosive where able to get into the nooks and crannies then it might not be an issue.

I've had a number of pieces done with the plastic medi and sandblasting combination. Like Bob said, make sure the guy doing the blasting is experienced in doing old tin. Definitely worth the extra searching and/or time and travel to get it done correctly.

we have just finished our media blasting building. media is the way to go. walnut shells are for engine parts and such. using it on sheet metal will drive oil into the metal. i do not recomend walnut shells. remove your paint with media and then hit the rust spots a low presure with fine sand. any surface rust on flat areas can be polished off with the 3m system. platic is the only thing i know of that wont warp metal.

as far as dipping goes we tried it several times. each time they had a new system that was trouble free. each one had bubbles later. ask them if they will warranty your paint. i will never chance it again.

You are correct Bob, if a corrosive gets between two layers it is tough to get out and can probably bleed in the future. We havent made the 3 or 5 year mark yet so we cant give a firm answer. We do see that problem with our powder coating.....bare steel has enough oil on the surface to outgas during the powder coat cure and cause bubbles.

Since the clearance is tight where panels overlap and are spot welded, there is probably a capilliary (sp?) event happening that makes the dipping solution very difficult to flush since there is no flow of liquid thru the joint....only into it.

BUT which is better? Little grains of glass/sand/beer bottles OR some acid? Both sound bad for paint.......makes me want to get an aluminum Cobra and never paint it!!!!

So Shine, where do you purchase your plastic media from? Maybe I can contact them and they might be able to put me in contact with someone local that can do the media blasting for me. Too bad your shop is too far away, I wouldnt mind sending you the business. Oh well, I'm still searching.

i buy from canfield and joseph composites. there should be a supplier in your area. not many media shops around. we had to build a booth and hopper for it and you have to have at least 185 cfm. if done right it will knock some surface rust off but we clean up and switch to a product called star blast for rust. we're offering blasting/rust removal with dp90 sealer and lizzardskin insulation. our hope is to take the car from yard art to clean and sealed so it is protected and ready to start on.
you can go online and look for composite sales companies. should bring up a directery of suppliers. let me know if i can help you find one.
try compomat.com

Quote:

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Originally posted by shine
i..... you have to have at least 185 cfm. ......

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I'm gonna bet you meant PSI rather than CFM, the best Kaeser screw compressor I ever had only did 45 cfm @ 125psi, which is a gang of air.

it is a diesel powered c/p 185 portable. it has a rating of 185 cfm . you only use 20 to 30 psi but it takes a lot of cfm to supply a 1 inch hose.

I do not want to do any advertising that is against the rules on the forum, but I may be able to answer some of your questions on media blasting or where to get the supplies if you want to PM me or you can email me at the following address.

David.Smith@abrasivesandequipment.com

racer dave, i'm trying type 5 melanine and have'nt used it before. i was told it was a little longer lasting than type II urea. any truth to that :)

shine

Sorry to take so long to reply, I was out of town until this morning.

Melamine is Type III, (Type V would be Acrylic), and yes it will last a little longer than Urea. Urea is a 3.5 on the Mohs scale, compared to 4.0 for Melamine. It is not likely that you will notice a huge difference, but if cost is pretty comparative from your supplier then Melamine will be your best bet.

shine is right about the amount of air required. The nozzle at the end of the blast hose is the determining factor in the volume of air that will be required. Obviously, the lower the pressure you want at the nozzle, the lower the cfm requirement will be. A #8 (1/2") nozzle will require 338 cfm to operate at 100psi as opposed to 195 cfm to operate at 50psi.

racer dave, i have type v 16/20 . this will be my first time with it and went with what was recomended to the supplier. i will be doing fiberglass and sheet metal both. trying to find the happy medium . [ no pun intended :) ]

shine

Type 5 (Acrylic) would be a good choice for you since you are doing both fiberglass and metal. Acrylic is one of the softer and lighter plastic medias out there. Due to its light weight and softness it will not be as harsh on the gel coat of fiberglass. You can eat through the gel coat if you are not careful, especially with some of the harder and heavier types of plastic.

It will be a little slower at removing thick coatings or hard coatings (such as powder coatings) than Urea or Melamine. But the difference will not be very much on typical automotive applications.

All in all I think you have found a HAPPY MEDIUM. (pun intended)


David
:LOL:

thanks david. i have a 54 vette to do i'll keep you posted.