Question:  Are You Blasting for Surface Preparation or to Clean A Surface?  The difference between the two is critical for success.  Lets quickly look at them one at a time.

Surface Preparation:  If you are blasting for surface preparation, you are trying to remove all contaminants, as well as prep your substrate to receive a coating.  This means going to the manufacturer of your coating  to find out the ideal surface profile for the coating you are going to use.   Too much profile will result in premature coating failure after the liquid in the coating dries and shrinks, exposing the peaks of the surface profile.  Too little of a profile will also result in premature coating failure, causing the coating to essentially peel off early, as the coating cannot get sufficient “hold” onto the surface.

This is why many painters will buy paint only from reputable paint companies, as they have the technical data on their coatings and can quickly tell you what your surface profile needs to be for maximum adhesion and lifespan.  The percentage of liquid to solids in any given coating will dramatically affect how much a paint shrinks when dry – this is not the time to guess!

Commonly purchased abrasives for surface preparation often include aluminum oxides, crushed bottle glass, coal and copper slags.

Cleaning Preparation:  Here the goal is to simply clean the surface without changing the substrate.  Often abrasives like glass bead, walnut shell, or plastic grit can be used in such cases, depending on your grit size, pressure, angle, etc.