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!

Aluminum oxide is VERY aggressive, get ready for a lot of metal work to smooth out the craters.. Check into blasting soda, or do the walnut shells.

http://www2.northerntool.com/product-1/200306426.htm Here is a link to the soda media

if you don't have one, the biggest exspence will be the compressor you will need to adquately run the pot, and not be on a continous duty cycle. check the requirements that are usually provided with any air powered device to ensure compatibility.

When you are ready to media blast, rent a monster construction-site compressor, like this guy did:

Shop Talk Forums "Race Look" Beetle

I've used the gravity style hopper and they are horrible if you don't have enough air volume. One day's rental on the big 50HP compressor units is low if you prepare everything and use the whole workday to get it all done.

I'd stick to walnut shells because there is no chemical issue to deal with, and it won't make a moon surface. With enough horsepower on the compressor, you WILL get all the paint and rust off.

I'm running a 1.5 HP Compressor on a 250 Gallon tank; I will check and see if that is enough to push thru a Pot...

Hmmm... I like the baking soda idea, and it's the same price as the aluminum oxide, plus the residue would (hopefully) dissolve with water???

So, still the question... how many pounds of this stuff am I going to go thru to strip the exterior of a typical 914??? Guess the answer is "Until you are done" but I would like to sort of plan my budget in advance...

If you trap the media, you can generally run it through the blower again and again.

Media is going to go EVERYWHERE. Tarp off your area like you were painting, and wear a hefty mask.

I found it easier to use aircraft stripper and 3M disks. A lot cheaper, too.

Zach

that compressor rental is a good idea. you know you're never going to have to stop blasting and wait on the compressor to catch up. repeatedly. i bet a car could be done in a day or less. it will go pretty fast. invest in a canister/element breather. not a particle mask. mask any areas off with heavy pastic and duct tape to keep the bulk of mess out.

Baking soda is a "salt", so you should be very careful to rinse the car very thoroughly, otherwise it will exacerbate rusting. Ideally, you use very pure water to rinse the car, or even slightly acidic (add vinegar?) to neutralize the baking soda.

That's why I'd go with something chemically inert like Alumina or Walnut Shells.

Hmmm... I like the BIG Rental Compressor idea, and get 'er done in a day or two... I could always get the setup, and test everything with my "baby" compressor, and then once I knew it was all good, hook up "Big Bertha" and annoy the hell out of the neighbors!

Actually, my shop is in a commercial area, so guess I prolly wouldn't even do that!

Wellll... back to walnut shells, which are locally available, and cheaper (for the same quantity) than the soda or the Alumina stuff...

Guess I could always use the Alumina on the underpan and wheel wells, and use the walnuts on the body panels... Once I get her cleaned up, I need to spray everything with some long term primer, as I prolly won't get the body work done before winter, and I don't plan to work on it over the Winter months... bones are too old for that!

Any suggestions as to a brand of primer to use as a storage coating? Figuring most of it will get sanded off again come Spring...

with the huge volume you can move up to a presure pot. much, much better. you can prob get a pot where you rent. then you have to ask 'why buy at all?'. call around.

k

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.

I have generally had better success with pressure type pots in the past than suction, but agree air compressor use is enourmous. I recently saw an alternative to compressed air that looked interesting. It used a pressure washer with a sand siphon. The advantage is no air compressor and no dust. The disadvantage of course is water and sand in your car. The dust issues with a regular media blaster are pretty bad and you really need a respirator so the pressure washer alternative looks interesting.

Hey, all great info! I will definitely want to get down to White metal, so I guess that I will be using something heavier than walnut shells, and worry about smoothing and filling after I get it clean. I too will practice on the less noticeable parts of the car, and see how it looks and feels.

I some panels are so thin that they "blow thru", then i will need to replace them or weld them up afterwards...

Great advice, all! Keep it coming!

Yeah! Keep them coming!
I'm gearing up for a media blasting this winter.

FYI soda blasting requires a completely different setup then sand walnutetc. Also more $$$ I believe. I have sandblasted several cars with aluminum oxide and can assure you it can be done without damaging the panels. Guys who warp body panels DO NOT KNOW WHAT THEY ARE DOING !! DO NOT point the nozzle directly ( 90 deg)at the panel, strip using an angled ( close to 45 deg) pattern. Use around 40 lbs pressure, this will vary somewhat by the blaster and tip size. Do not use the harsher oxide. It comes in several different consistencies. Use the fine to medium grit. Keep the nozzle moving, you will warp the body by concentrating on one area until it is clean. Make certain you have a moisture seperator before the air inlet for the pot. Wet sand doesn't shoot too well. Move around to reduce heat and pressure. Be forwarned. It is nasty, hot, dirty, nasty, sweaty, dirty werk.

I'm thinking of getting one or two of those disposable white "paint suits", and a full face respirator, and wait until the temps are somewhat cooler. My shop is large, and I can hang plastic curtains to contain the debris. In fact, the ceiling is already covered with plastic, so just need to do the side containment.

Very good tips! Should help out a LOT when i finally get into throwing stuff at the car! I noticed the instruction book on the Pressure Pot I am thinking of buying specifically called for using the 45 degree angle of approach, so that must be a very key point. And just like a paint gun, Keep It Moving!!! All makes sense!

Easy home blasting method:
If you have one of those 10x10 pop up canopy's or bigger. Set it up and get a long polyethlene tarp ( you know the blue ones at Home Depot ) and drape it around the canopy frame at the roof area like a dress and around the car perimeter to the ground. Blast away! I always like to have one side open for fresh air.

I use a shop vac to recycle the media. Filter all the blast junk out of the media through a fine screened cooking strainer as you dump the spent media back into the hopper.

A good media to use is DuPont Starblast. Fine (sieve) is available I think up to 180 grit. Starblast is processed to not have sharp edges and leaves an ideal priming surface.

Always use a media with no or low silica. It will shorten your life if you do not wear the proper respirator which should be a supplied air at least Type D supplied air. Always wear a hood with a lens. Trust me getting hit with 500 mph media hurts.

A Canopy! Great idea! I bought one a couple of years ago to take to our nephew's baseball games... just get a couple of blue tzarps and I am in business...

Thanks for the tip on the Dupont Starblast. I will search it out and see if I can buy any locally! I figured that recycling the media would be pointless as it would disintegrate when it hit the car, but i might at least try it. Maybe mix half and half with new media to keep the effectiveness up???

We used to blast the airframes of B-25's with walnot shell. That stuff is awesome. We built a "cabinet" with two semi trailers with plywood at ground level and lower sides and tarps. You need to protect your body from dust, sound and projectiles. It is really important to sweep your area first and filter the media after you collect it removing junk that will either clog your gun or damage the surface you are blasting. It's a giant mess.