Hey Mike H
Now I’m getting more nervous about starting my tanks because that’s what I was thinking about doing. So we don’t need to assemble the tanks with clecos while the proseal is drying? Since this will be my first set of tanks to build, how do I set all the ribs in place and set all the Rivets for those ribs all before the proseal dries on me? Please correct me if I’m wrong here but if we only work with one rib at a time meaning apply the sealant, place the rib & then set the rivets how do we slide the other ribs in place without messing up the bead of sealant?
Do I need to use Substructure and Tank dimple Dies or the regular dimple dies?
Also I know you are primering the Exterior skins but did you primer the exterior of the tank skins before you started assembling the tanks?
DO NOT cleco the tanks together and wait for the sealnt to cure prior to riveting. Use regular dimple dies. I applied the Akzo 463-12-8 solvent resistant primer to the exterior after the tanks were complete and held air for a few weeks.
Mix a small batch of B2 sealant that will be used to install the stiffener angles. Place the mixed sealant on one end of some clean cardboard and transfer a small amount to the center. Use a sealant roller and roll out the small amount to achieve an even thin coat on the roller surface. I prefer a rubber surface roller. This roller can be cleaned with acetone and reused multiple times
https://marshalltown.com/2-flat-commercial-grade-solid-rubber-seam-roller-durasoftr-handle.
If you work fast, or you have a riveting partner you can shoot all of the stiffeners in before the sealnt starts to set and gets too thick. If working by youself, only mix a couple of ounces at a time and work untill the sealant starts to set, that way you don't waste lots of sealant. Same process for the ribs, with a riveting partner you can install all but the two end ribs of one tank using one batch of sealant. Start with the inboard most, or middle rib, then alternate working outboard.
Now that you have a even coat of sealant on the roller, you will use it to apply an even, thin application of sealant to the mating surface of the stiffener angles. There is no need to apply the sealant to the skin and the angles or ribs, application on one surface provides ideal sealant thickness. It is way easier and much less messy to roll the sealant on the rib and stiffener flanges, there is no need to mask the parts as you would if you applied the sealant to the tank skin. Using a roller to apply sealant will result in an even application ranging between .005" to .020" depending on technique and applied roller pressure. If you prefer to have some sealant in the rivet holes you can apply the initial coat, then turn the roller sideways and lightly drag the edge of the roller down the part to smear some sealant in the rivet holes, then run the roller across the part again to smooth out the seant. Remember, "bigger the glob, better the job" is not what we are looking for here. As long as there is an even thin coating on the flanges, you will have sufficient squeeze out when the rivets set and draw up the structure. Keep in mind that the sealant application is only effective in the leak path area. This means that 1/8" fillet seal that that many builders blob on the the interior ribs is not really doing anything becuase during the riveting process the thin fay sealant application was squeezed into the rivet hole and out around the flanges of the rib sealing the only possible leak paths to the rivet head. Also an excessive amount of sealant in between the structural components will weaken the stucture by allowing the structure to flex, and will cause smoking and leaking rivets.
Using a cleco in every hole install the parts,
then wipe out any sealant in the dimple prior to installing and shooting the rivets. Do not use rivet tape and pre-load the rivets in the holes since there may be some squeeze out into the dimples of adjacent holes as you rivet the parts together. Starting at the forward most hole, remove a cleco and shoot the rivets one at a time working forward to aft, repeat untill the rib or stiffener is complete. Wipe the squeeze out off of the skin and tools with acetone or MEK as you go and before the sealant cures.
After you get the stiffeners and interior ribs installed you can install the outboard close out ribs using the same technique. Apply a generous fillet seal to the skin to close out rib seams and wait a few days for it to cure prior to instaiing the aft tank wall. It is not necessary, but if you want to back seal the rivet tails now is the time to do it. I reccomend buying a pint of A2 sealant for this application. I prefer to overcoat the rivet row as opposed to dome sealing individual fasteners since there is more surface adhesion area and less chance of the sealant seperating. Keep in mind that you must ensure that there are zero voids around the rivet tails, or else you are not accomplishing anything. A paint brush with the bristles cut off short works well for applying the A sealant. A circular application motion around the rivet tails will help you obtain proper adhesion and minimize voids, you can then smooth out the sealant in a back and forth motion.
Install the rear tank wall using a slightly heavier than normal application of sealant. In this application I reccomend an even coat of sealant on the skin flange as well as the rear wall flange since some of the sealant will be displaced during installation of the part. Install clecos in every hole to draw up the parts and squeeze out the excess sealant. Duckbill pliers wrapped with masking tape can also be used to help draw up the parts and push out any voids in the sealant. Working from the middle outboard, remove the clecos and squeeze the rivets in the flange one at a time. Install the blind rivets wet with sealant, wipe off the excess and admire you're work.