Organization is key. It's not difficult if you are prepared and don't rush. Plenty of time to get everything right, given how long it takes to set up. I didn't find the tanks on my -6A all that difficult and other prosealing tasks since then have been a snap. Nice shop, by the way.
Thanks for the kudos.
I was concerned about set up time but it is a none issue, at least at 75F and using Flame Master out of the can. The stuff was still workable after an hour but it was getting stiff.
For those just tuning in, this effort is motivated by chronic paint blisters at rivets in the fuel tanks. I am replacing QB tanks built in 2002. The cause of the phenomenon is not known and is under study by some guys here and at Vans.
In the background of the second image is a view of the one of the old tanks after I opened it with a 5" hole saw. The sealant work done back in 2002 actually looks good although it does appear it was thinned and there definitely was less of it used that what I am using. Until the interior could be examined I was undecided on whether to repair the old tanks with more sealant, as has been done successfully, or rebuild.
What prompted the decision to rebuild is completely unrelated to the blisters.
What I found in the left tank were 4 of the 7 ribs deformed and slightly collapsed. That was self induce by me before the airplane first flew back in 2003. Some fuel had been poured into that tank to facilitate test running the Subaru engine just installed. When it came time to weigh the airplane, the remaining fuel was removed by disconnecting the fuel line at the engine and pumping the fuel out with the electric pump. While this was merrily going on I heard this ominous whomp sound - wow, the top of the tank was slightly indented. I immediately stopped the pump and opened the cap and it all popped back to it original shape. What happened was the result of a piece of masking tape across the fuel vent line to keep mod dabbers out.
Much to my surprise, the event did not result in any fuel leakage for quite some time, like maybe 4 years. When it did come near the leading edge, it was repaired by sucking some green lock tite at each leaking rivet. There were 4 or 5 and it worked.
Now did that event have anything to do with the blisters appearing? I don't know. The evidence would indicate not. The right tank actually has more blisters than the left tank with the damaged ribs. Most of blisters are at the aft bulkhead flange, top and bottom. Almost every rivet at the right aft bulkhead has blistered top and bottom.
The sealant used in 2003 was definitely thinned. The final finish is very smooth and the color a light tan. Clearly, it had been applied with a brush. I believe this is a technique used in some production aircraft and is not a local anomaly. Perhaps the stuff had been thinned a bit too much, there is some cracking evident at corners and some crimped rib edges are open where right tank rib rivets have blistered. Curiously, left tank rib rivets have not blistered as much and there are open edges everywhere after the vacuum damage to the ribs.
Perhaps, as one theory goes, it could all be caused by external contamination. I don't know.
I do know what I am assembling now will have a lot more sealant everywhere and none of it will be thinned.
