I have an ALC brand pressure blaster that will hold 100 lbs of sand. I also have a 10 horse compressor. I have only ever used sand in this unit it seems to work real well. My questions are in regards to using other types of media such as plastic or walnut shells. Can I do that with this machine? What size / hardness of media works best? What size tips are best? What pressure is best? Where is the best place to get this in Iowa? And finally, What is the expected cost difference from sand. I need to remove surface rust from sheet metal on a 34 Chevy. (it is covered, no paint on it) I understand all the dangers of warping it with use of sand. I need some type of a baseline to start with if using other media. Anyone?

Any type of media like sand, aluminum oxide or any other abrasive will most likely warp the metal. You want to use walnut shells, plastic or even better yet, soda blasting.
To do shells,plastic or soda you will have to change the tip, but that's something you will have to ask around for.

As a general rule, sandblasting a car body does not warp the metal when DONE PROPERLY. It is the operator that gets too close or holds the nozzle in the same position for too long that creates excess heat that causes the metal to warp.

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soda is a no-go as it will not remove his rust issue. Any blasting media can warp metal if not done properly, some more than others.

Especially if the operator is used to blasting structural steel with a big high volume commercial compressor, then he is given a car body to blast......and what happens?

Vince

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Just ask Shine his "opinion" on sand.
Which I have to agree on.It's "old tech" and a health hazard besides applying a larger than necessary anchor pattern.
There are plenty of "safer" blasting medias available and most times,it comes down to what you can get localy because you can purchase most anything BUT the shiping is what breaks the deal unless of course your buying pallet loads.
Most are using the coal slag type product for blasting in general,especally where rust removal is involved.
If you have a Tractor Supply close,They carry Black Diamond media in 2 grit sizes,Coarse and Fine.
I use the Fine as it's the equivlant of 80gt and can be recycled as long as your not blasting greasy,contaminated areas or parts and does a great job for general work.If you plan on doing heavy equipment or thick structural pieces,the Coarse would be a better choice.
Initally,it is large particles but as you blast,it breaks down and actually does a better job on rust and especally pits.
Starblast is another good media but it's not generally available localy,Just have to check around and see.
As everybody has said,it's the operator and psi used that causes most warpage.Sand especally is a problem as your pounding the metal with tiny hammers and actually stretching the metal as if you were using a hammer & dolly.
I use blasting for most everything but "skin" type panels such as doors,hoods,tops,etc.Any large flat panels with thin metal should be sanded or stripped.
With your set up,you can really "get it on" and basically use the LEAST amount of psi necessary to remove what your working with.Nozzle size will just determine how much area you can do with what air supply you have,Most of us have smaller pumps and use a small nozzle to keep the psi up and removal is slow.With yours,you can use a larger nozzle and cover a larger area faster but you'll use media quicker so it's a trade off for efficiency vs speed.The pro's have either a booth with a floor sump to recycle back in the system or a big butt hopper to dump in 100's of pounds at a time with a very large nozzle to knock it out fast.
Paint removal is "easy" and requires as little as 40# or so but rust,especally pits,requires more psi,and that will be a "feel" thing reguarding the media used,generally 90 or less.