The effectiveness of any blast media is a function of the weight of the particle and it's shape and hardness. The energy of the particle to knock off rust or produce a surface texture (yield metal) is partly a function of its impact energy (particle weight and velocity)just like a bullet. Walnut hulls and baking soda are soft and light so they do best when used for well aged paint and surface debris that requires minimal impact energy. Rust tends to be too much for it without prolonged blast times and excessive media consumption ($$$). Abrasive grits come in a wide range of screen sizes and one of these can be used to remove whatever you have on the metal without the metal distortion if used carefully. The blaster can also select a nozzle-to-part distance and air pressure to further balance the rust removal rate and metal distortion. A qualified blaster can select the proper blast media and size, air pressure and stand off diatance to do the job correctly. And to further complicate things, you need to know the nature of your primer to properly select the final surface texture. Paint adhers two ways: mechanical adhesion and chemical adhesion. Blasting produces the mechanical "tooth" and cleanliness allow for the chemical adhesion. Epoxy primers are generally applied thicker and have higher viscosities so they will cover the higher peaks produced by coarser blast media. And coarser media have higher removal rates (cheaper job)-although higher risk of metal distortion (uh-oh). So, use a good qualified abrasive blasting contractor! It is usually worth it. Learning on your "baby" is probably gonna hurt.

John M. Schluter