Below are some step by step pictures and description of how I am sealing the tanks. Granted this is only one part (the fuel cap flange) but the steps apply to all mating surfaces. The idea is to get two barriers of sealant so that if one fails the second will prevent fuel leaks. Some areas this is not really possible but in most it is.
|End ribs with fuel penetrations installed/sealed
|First step is to get the tools out. This is a 10cc syringe that I use as a mini caulking gun. Oh, and lots of rubber gloves...
|Syringe loaded up with enough Sealant for tonight's sealing steps. Tonight I installed the fuel cap flange and the drain flange.
|Its not really visible in this picture but this batch of sealant prevents the fuel from leaking past the rivet holes. This is a bead of sealant around each dimple. The fuel flange will sit on top of this area.
|Each rivet needs to be sealed as well so in this picture I am dabbing sealant into each dimple on the outside of the skin using a q-tip twirled in sealant. This is done just before I put the rivets in place.
|Rivets pushed into place and the area around the rivets is gently cleaned up with MEK so that the tape used to hold the rivets in place (and protect the skin while back riveting) sits tight against the rivets and skin.
|And finally this is the "cap" of sealant that I place on top of the shop head of each rivet after it has been set. This acts as the second barrier for the rivet holes.
|This is the drain flange inside the fuel tank with the sealant cap applied.
|And this is the outside of the same drain flange. If you look close you will see sealant around each rivet as well as the edge of the flange. This is after I had used some MEK to clean up the excess sealant that squeezed out.