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Blasting Media

September 24, 2010 | Troubleshooting & Repair

By Roy Smalley

Sand and air pressure develops substantial heat and will warp thin gage sheet metal. Structure that is welded like pan/longitudinal sections can be sand blasted, as can some, perhaps most reinforced inner sheet metal. Sand blasting thin gage sheet metal can be done, but is always a high risk (that is the exterior skin of the body and bolt on panels). I would never use this method to clean a car overall, if for no other reason, removal of residue.

Soda blasting does not generate much heat but it will not remove rust. The same holds true for plastic media blasting. Neither will warp thin gage sheet metal with a reasonably qualified user. Soda blasting residue is easy to clean up. Plastic somewhat more difficult, but much easier than sand.

All will etch lead depending upon care, air pressure and size of plastic media which can be fairly dramatic. (There was an excellent article on plastic media blasting in the Registry a couple of years back.)

Dry ice is coming on and being offered as a portable service in some markets. It will effectively remove paint and undercoat materials and may be superior to all. I understand it is somewhat effective in removing grease and oil buildup. I have not had first hand experience with dry ice, but it is being used in Europe effectively.

Rust can only be removed by cutting it out, sandblasting (very few operations actually use "sand" as it is illegal in many areas, substituting other hard abrasive materials of various grades) or some other mechanical means, or by immersion in a chemical solution that dissolves the rust through chemical action. 'Encapsulation' of rust is just that, until water finally and inexoriably finds its' way in...

On the vast majority of cars there is rust either showing or not, hiding in the flanged/enclosed areas that were never painted that started rusting the first time moisture was available, so a combination of various methods may be necessary to remove all the offending materials prior to repair and refinishing.

Rust is a continuing potential problem even in highly qualified restorations, and it is virtually impossible to prevent that potential over a long term. A rust free 356 does not exist.