its going to take alot more air than 6 cfm that is min.@ 60psi. what will happen is once say a 20 gallon tank is at 150psi. You have the blaster at say 100- 125 That takes 25Cfm at 90psi. You empty the tank to 60 psi and the 6cfm air supply is running none stop and the 60psi will be not enough cowbell.
So you can do a little than wait for it fill, do some more etc.
A 25cfm to run a full 90 psi sand blaster takes a rather good air supply. To much $$$$.