after blasting get into epoxy as soon as possible. no need for etch primer. just turn the fan down and flood the insides. let it run into holes and stuff. one of barry's tricks is to mix a qrt and pour it into the door [ off the car] and run it around all the corners. i was told by my abrassive supplier not to use walnut if it is to be painted. he stated there was still oil in the shells. anyway the starblast works better than anything else i've tried. it is very fine and gets the pits and cracks clean. i epoxy everything the next day. good luck.

if you use walnut hit it with 80 grit before shooting it.