The Cost of "DIY" Media Blasting..., or Should I buy the equipment for only one car project... Options

[73Phoenix20]

I know some of you folks will have some advise for me on this subject...

I need answers to several questions regarding media blasting...

1. Is the 'Pressure Pot" Blast System significantly superior to the gravity fed system?
I can get either one at Harbor Freight (and prolly other places) for about $50.00 difference, which is trivial, IF the Pressure Pot system really works better...

2. I can get Aluminum Oxide media for $40 per 25lb box... how much surface area will this cover, assuming I am removing the factory paint down to bare sheetmetal? 5 square feet? 10 square feet? More? For an easy example, will 25 lbs strip the hood of a 914? Or maybe the hood and trunk (top surface only)?

3. I can get crushed walnut shells for about $20.00 per box, but i assume they are much less effective? How much less? Will it take twice as much in walnut shells vs. aluminum oxide?

4. Luckily, I only need to strip the exterior, as the interior is in fantastic shape, and I am repainting to original color. What is the best material to use to mask areas that I don't want to get "accidentally" blasted? Heavy duct tape? Multiple layers of heavy plastic sheeting?

5. Will Aluminum Oxide risk warping of the sheet metal due to heating? I understand walnut shells won't warp panels? True or not? If they are only marginally less effective, and half the price, I guess I will go with the walnut shells?

Prolly more, but that is all I can think of right now! Thanks folks!

[Richard Casto]

I am going through this right now. I had initially planned to have someone else blast the entire car. But because I live in an area with such high humidity (Central North Carolina), I was worried about surface rust appearing before I could paint the car even after using Ospho/Metal Ready treatment. My ideal solution was to work on smaller sections of the car (i.e. interior floor, exterior floor, interior front trunk, etc.) with each section being stripped to bare metal, treated with Metal Ready, do rust repair, retreat with Metal Ready as needed, POR-15 (as needed) and then spray with Epoxy Primer and then move onto the next area. In that the entire car would not be bare metal all at once. Once done the car would have a complete coat of Epoxy Primer and then I could move onto pre-paint body work, etc. without fear of rust.

I currently have one of the cheap pressure pots from HF, a large 220V compressor and am using fine coal slag (Black Diamond brand) as my media as it is very cheap. I also have built a tent using PVC pipe and plastic in my garage to keep media and dust to one area. I would like to try out some Aluminum Oxide, but just haven't picked up any yet. My blast cabinet uses syphon and I can see how it is not as efficient at the pressure pot. The pressure pots are cheap enough that I would buy one if you plan to do much blasting outside of a cabinet.

I have zero media blasting experience other than some small stuff in my blast cabinet so I am learning as I go and trying to read up online as much as I can. I have tried to read up on different media and also put together this page on the 914 Wiki regarding blasting media...

http://www.roadglue.com/wiki/index.php/Blasting_media

From what I have read, I can see that using Walnut Shells and/or Sodium Bicarbonate will work for paint but will not work on rust. I would expect that the Sodium Bicarbonate to be an expensive route (as you can't reuse media and it is expensive in the first place). That if you want to reuse media AND not etch the surface (aka surface profile), that you can use something that can be reused, but at a much lower pressure. For example with fine coal slag at 35 PSI, a single pass will NOT get through the paint and so far is not etching the surface. Cranking the pressure up to 70+ PSI WILL get through the paint in a single pass AND will etch the surface. You just need to find a combo of media, pressure and technique that works for you. For areas that have rust, I do need to use higher pressure to get down to a "white" metal (which by definition is cutting a bit past the surface)

So from what I have learned so far it is a combo of media, pressure and technique. I am learning on areas like the bottom of the car and hopefully will know what I am doing by the time I attempt something like the hood. I probably am going to look into using paint stripper for much of the easy to get to areas and use the media blasting to hard to reach areas.

Regarding the entire "warp via heat" thing. My understanding is that the process does not generate enough heat to warp. But high pressure AND dense media AND pointing the stream at a 90 degree angle to the panel is like thousands of heavy little hammers hitting the metal and that will warp it or even cut through thin panels.

If you plan to have the entire car blasted at once, it probably will be cheaper to have someone else do it (I think I was quoted $450 for the entire car with it being totally stripped - no wiring, seals, etc). If I was to do the entire car at once at home, I would explore the idea of renting some type of rig to do it.