I have been dreading doing this proseal stuff. So, I finally just went ahead. Scuffed the tank surface with 2 inch scotchbrite wheel. Cleaned all stiffeners and tank mating surfaces with MEK. Cut up a half dozen paper towels into 2 inch squares for mopping up later. Soaked all rivets in MEK. Plans call for 426AD3-3.5 for sitffeners. On the two new stiffeners I had to fabricate from 063 angle, I used 426-AD3-4 rivets. Wear 3 or more pair of nitrile gloves so you can peel off and keep working when they get all funky with proseal or ripped up. I spread proseal on the tank skin inside along rivet holes, turned skin over and dabbed a small amount into each dimple. Inserted rivets and covered them with rivet tape. Turned skin back over and spread proseal on each angle using popsicle sticks. Positioned two stiffeners at a time over the protruding rivets. Squished down forcefully with my fingers to set the proseal. Started in the mddle of each stiffenerr and after making sure the back-riveting steel plate was properly positioned under two stiffeners at a time, I used the back rivet set to set the rivets. Used 40 working lbs of air with the 2x gun and set the rivets using a count of "one thousand". However, you only are able to say the word ''one'' when you start riveting and the rivet is set. When the 2 stiffeners are done, I use the mopup squares wetted with MEK to clean the rivet set. Then, I turned the tank over and pulled the rivet tape off the 2 stiffeners, cleaned the heads with more of the 2 inch squares wetted with MEK and repeated the process on the next two stiffeners. I used the rivet guage to satisfy myself the rivets were set properly. They were. No mistakes.
