Not sure at all what cob blasting is. I presume some sort of sand.
Anyway, cedar shakes are about as fragile as potato chips and should be handled with extreme care. I have even had difficulty using a power washer on them.
You can wire brush them to get off the main stuff. Consider a product by Sherwin called woodscapes. Made for this type of siding.
© 2017 Renovate Your World LLC