This is where I must respectfully disagree with you Scott. So much has been written on this subject over the years. It is not that complicated an issue despite those who offer this theory or that, or those who confuse and dazzle us with their arcane technical knowledge of proseal. Proseal is tough forgiving stuff and it takes some doing to screw it up, but it MUST be applied correctly in the first place. An awareness of proper fay sealing and fillet sealing and encapsulation is absolutely essential. I continue to remain convinced that it is nothing more than improperly applied proseal that is the root cause of the blistering problem, nothing more. Some much conversation has elapsed over the years that the newbie who never so much as looked at proseal in his life until he built his first tanks or bought a QB is understandably confused. Certainly paint formulations have changed over the years, no one can dispute that. I maintain that if the proseal is properly applied in the first place, fuel or its fumes should not come into contact with newly formulated high tech paint in the first place.
Partly as a result of my urging, Dave Domeier built new fuel tanks heeding my technical advice. A year later he continues to report no paint blisters have occurred and I doubt that blistering will ever occur. The only thing that changed was his increased awareness and application technique.
All one has to do is review the graphic images in posts 100 and 163 in the famous paint blistering thread to understand how sloppy craftsmanship shouts out loud and clear as to the problem. Beside, the paint blistering problem has occurred for a long time, long before new paint formulations came onto the scene. Rerread this 1980 newsletter from the Pazmany folks regarding the vexing issue:
http://www.pazmany.com/newsletters/PL-1_and_2/64.pdf
No one likes to be told they are doing something wrong. Without proper training in the application of proseal it is a wonder even more cases of paint blistering have not cropped up.
I have never said blisters haven't been caused by poor workmanship. I know of tank blisters that have had fuel in them when punctured. It is pretty obvious those were caused by workmanship issues.
Where I think you are totally wrong Rick, ismaking the assumption that because evidence of poor workmanship has been detected, that that is automatically the cause of all paint blisters.
I am also well aware that tank blisters are not a new problem, but until more recently, they were a rather rare problem.
I will throw out a few questions of my own that I think need answers if we are ever going to solve this problem.
- I have been involved with RV construction for over 24 years. It is only in the last 5-7 years that paint blisters on tanks have become more than just an occasional occurrence ( BTW, all of the early instances I can remember all had wet fuel within the blister so it is obvious what the cause was).
So, considering that only in recent years have online forums made it possible for amateurs to get more educated about how to properly seal a riveted tank...
Why weren't we seeing this through out the 90's when the volume of RV's being built really started to grow. Was everyone just lucky?
- I know of at least one instance where an owner contracted with a popular professional fuel tank assembler (who has probably built hundreds of tank sets by now), to build him a new set of tanks (his originals had lots of paint blisters). The new tanks were repainted by the same painter that had painted the airplane the first time (I assume with the same paint system, but I do not know that detail). The new tanks blistered.
Should we assume that the professional builder was less lucky than thousands of other amateur RV builders that have not experienced paint blisters on their tanks?
One other data point.. take it for what it is worth.
To date I have built or been directly involved with building at least 20 sets of RV fuel tanks.
On every one of those tanks, no special effort was taken in regards to proper fay sealing and fillet forming. I did not cover each shop head with sealant after setting. I did not use tank dimple dies.
What I DID do, was clean all parts very carefully (Naptha). Used a carefully applied layer of sealant on the rib flanges, and then was very careful inserting them into the skin so that no sealant was wiped/transferred from the rib, and clecoed as needed to develop a net fit of the rib to the skin. I then removed the sealant from the dimple depressions <gasp> before inserting the rivets, and set the rivets with the sealant uncured.
There has never been a leak or paint blister in any of these tanks.
I know this goes against standard practice, and I am not advocating that builders use this procedure. I am just offering it as another data point, to suggest that "just because someone hasn't used your recommended procedure, doesn't mean they are doomed to have paint blisters".
Was I just luck? (like the thousands of RV builders prior to paint blisters becoming a recognized problem). If so, I need to start spending my vacation time in Vegas.
Bottom line....
I don't disagree that some of the blistering has probably been caused by workmanship issues.
Where I do disagree, is categorically assuming that all of the paint blister issues up to this point could have been prevented by simply using the assembly techniques you advocate.