You would want to use the .03 or .04 nozzle size with this sandblasting kit in conjuction with your pressure washer. I would suggest running your pressure washer at full 3000 psi especially when cleaning the concrete surface. You will more than likely want to lower the pressure down to about 2500 psi when cleaning the aluminum door you mentioned. I would suggest starting at a lower psi and see what amount of pressure performs well.