Soda Blasting vs. Sand or Glass Blasting? What is your Experience?

[SkylinerRon]

Never blast with sand it will kill you. Walnut shells and fine glassbeads take forever.

Aluminum oxide and silicon carbide are the most effective. Blast them outside and
put a tarp down and reuse the beads.

Always use a full facemask. A supplied air one is best. Anyone who tells you to use a $.79 mask is
not your friend!

Media WILL get into everything, no amount of tape will stop it.

If you have good solid paint on your car now you may not need to go to bare metal.
Scuff it well and throw on some sealer first and go from there.

Goodluck,

Ron.

[djfordmanjack]

DJ...I guess we'll have to agree to disagree on the heat thing. If you stress relieve a piece of sheetmetal on one side only, it will warp.

Rich, that saying makes just a great foundation for proper discussion.
I am getting your point somwhat. are you saying that false use of sand blasting and pressure will rather stress relieve the side of the metal that has been blasted than shrink the whole panel because of excessive heat? it makes sense. I have a feeling though that metal reactions will effect each other and both heat and stress relieve could come into play. I'll show some private pics of a 1950 VW split window I had to bodywork for a customer. it had been damaged badly by the blasting guy, getting warped and being beaten back out with a stupid hammer. go look for yourself. that is just the usual problem occuring with false blasting procedure ann I know that this was ruined from INSIDE. so it speakes for your theory of stress relief. ( the inside got wider and therefore caused a crowned bubble to the inside).
Sorry for distracting from Johns request about soda. I think Rich's way of Zink etching the bare steel is a good answer about getting panels clean before filler and paint.
here's the panel pics though. so I am at least sure about how to REMOVE sand blasting warpage

[RICH MUISE]

I've been thinking about this off and on for a few days. Fact is, I don't know positively about anything, just a culmination of things I've experienced over the years. My years in Machine shop tell me stress relieving is a real issue, wanted or not( machined parts are commonly rough machined and stress relieved prior to final machining), and removing the "skin" from a surface will cause metals to distort. I can only imagine that sand blasting does stress relieve a surface, either from the physical hammering of the sand, or the heat. In either case as said, I don't know for sure. It just makes sense to me that it is more physical than heat.
As far as sandblasting, there is sandblasting and there is sandBLASTING. My 5 hp compressor does not produce a really high pressure even with the 40# pressurized sandblasting tank I have...at least compared to a commercial gazillion lb. pressure system. There is a huge difference in what a commercial system has the ability to put out...enough to severly damage any sheetmetal with just pressure alone. So I think it all gets back to does the operator know what he is doing and does he care enough to slow the process down enough to get it done without damage.

[Ford Blue blood]

I have to say, sand blasting will warp flat panels.  The heat just on the surface is the issue.  The sun heats the panels on the cars evenly and through the entire thickness of the material over a relatively long period of time.  Those disc with the ripples in them work so well because they heat the top of the "bump" faster, the heat and cool is a completely different reaction that causes the shrinking (do I need a shrink after reading this thread?).

I do not strip cars down to their bare skin.  If the paint is still on the car, has not rusted through something was done correctly at the factory.  I DA down to the factory primer and shoot urethane mixed 4 - 2 - 1 and let stand.  Old repairs become self evident, any filler is ground down to the metal to find out "why".  If there are large areas of bare metal they get etching prior to the primer.  The Ranchero bed was a complete blob of surface rust with some deep pits so blasting was the only way to clean it.  The blaster did a great job, no warped panels, a clean surface, and dust every where!

Bottom line, all the mentioned methods work, not sure which is better, just like tools, only as good as the person on the end of it.