[StingRay]

Most etching primers are not sanding primers and are very thin. Generally they are not for multiple coats either. Typically they are a thin coat put down for a primer surfacer to be applied over. Regardless on aluminum you want full coverage of a good etching primer prior to topcoat so it will need reapplication at least before top coating. Not knowing what specific material you are using it's tough to give good advise. Your material tech sheets are your best friend.