Below are the upper and lower engine cowlings for a Cessna 172.  Every rivet was drilled out and the cowlings completely disassembled to address surface corrosion.  The paint was removed then all parts were carefully soda blasted. The bare aluminum was treated with Alumi-prep then treated with Alodine 1200S. A two component polyamide epoxy primer was applied to all the parts.  A few days afterward all the parts were held together with Cleco's then riveted back together.  The cowls were mounted to the aircraft to line up the stripes then refinished.