The size of your air compressor will vary with the size of nozzle and type of blaster. For example, a pressure pot with a 3/32-inch nozzle may only need 7 CFM of air at 40 psi. A siphon-fed blaster may require double that amount.
That being said, it is always better to have more air flow capability than you need. For best results, I recommend referring to the specifications guide that comes with your equipment.
-Michael Sullivan, IKONICS Imaging