Weird paint bubbles. Looking for a cause/solution

rvbuilder2002 said:

( BTW, all of the early instances I can remember all had wet fuel within the blister so it is obvious what the cause was).

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That's a negative on that statement, Scott.

From the very beginning (2003-04) of examining this problem there was not a single reference to fuel in any of the blisters reported with this problem. They are dry, all of them. People who have had fuel in the blisters know what is causing it, they do not report here.

OK - if the culprit isn't inadequate workmanship, what is?

In the very early years of RV building, builders had a different attitude than since the introduction of matched drilled kits. They were more diligent because they had to be. Jigs were necessary and attention to detail was mandatory. The "dry" tank blisters are occurring on newer kit airplanes that are much easier to build. Building a good fuel tank requires some attention to detail unlike most of the rest of the machine where parts fit together perfectly.

OK - so a pro fuel tank builder had it happen. Maybe he slacked off a bit and did not get the aft baffle properly sealed. Seems like at least half the problem tanks are QB's by contract paid workers. We know for a fact some of those tanks were assembled way below average first time builder standards with little or not rivet encapsulation and with open seams between ribs and skin.

I submit, in the absence of convincing science pointing to product deficiency of incompatibility, the problem most likely is inadequate workmanship, especially at the aft baffle.

But as you say, it has happened to some very good builders. So I can understand your arriving at a different conclusion regarding the matter. The dry blisters are indeed an interesting mystery.

Intentional blister?

Suppose I put a dry flush rivet in the bottom of a soda can, prime and paint it, fill with avgas, put a lid on top and leave it in backyard for a while. Will I get a blister? Just curious if such a thing has been done.

David-aviator said:

That's a negative on that statement, Scott.

From the very beginning (2003-04) of examining this problem there was not a single reference to fuel in any of the blisters reported with this problem. They are dry, all of them. People who have had fuel in the blisters know what is causing it, they do not report here.



OK - so a pro fuel tank builder had it happen. Maybe he slacked off a bit and did not get the aft baffle properly sealed. Seems like at least half the problem tanks are QB's by contract paid workers. We know for a fact some of those tanks were assembled way below average first time builder standards with little or not rivet encapsulation and with open seams between ribs and skin.

I submit, in the absence of convincing science pointing to product deficiency of incompatibility, the problem most likely is inadequate workmanship, especially at the aft baffle.

But as you say, it has happened to some very good builders. So I can understand your arriving at a different conclusion regarding the matter. The dry blisters are indeed an interesting mystery.

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We have a communication failure.
Your very beginning and mine are very different times.
Keep in mind, RV's have been being built for a long time (we just celebrated the Van's Aircraft 40th anniversary ), so you can not assume that statements like this just mean the time period that you have been involved. By early incidences, I meant early in the history of RV's becoming popular When I first got involved about 25 years ago.
I was speaking of the time frame of the mid 80's to through the 90's.

The tank built by the pro builder developed blisters on more areas than just the rear baffle.

just for reference.

I got my QB wings in 2007 summer, not sure when they were actually constructed. I did absolutely nothing to them other than the simple balloon leak check. I did not fly prior to paint. In fact, No primer and No fuel in them until sept 2010...which was after they were painted in May 2010. Cleaned with hot soap and water and some degreaser prior to paint...several times. I don't recall the primer used, but think it was a PPG product, then topped with Dupont Base/clear stuff.

No blisters after 150hrs....lucky I guess. But also we were meticulous with cleanliness during the paint process.

Since I started this thread I thought I'd give an update on my findings/decisions.

During the annual downtime in November I will pull the tanks and have a local guy cut into the rear baffle and reseal. He will cut a hole in the rear baffle in each bay.

Then I'll seek out appropriate paint touch up. My plane isn't a hanger queen and it wears it's paint chips with pride A badge of honor for getting used a lot....if you will

My thoughts on a cause: my tanks were SB not QB. By the nature of the installation of the rear baffle, it's a bit difficult to get a good thick bead of pro seal and all but impossible to verify. You close it up and hope there's a nice bead in there.

Any voids can open up in time, I think. Hence my 6 yrs and 700 hours of bubble free paint. The vibrations from use and acro stresses could expedite this process, I think.

FWIW. The guy who will do my tank repair has a -6 painted with Endura. He needs to reseal his tanks too. He said the fuel leaks at the rear baffle also and leaves a blue streak. The paint is so strong (or porous) that the fuel passes through it. No bubbles, blue streaks on top of the paint.

Darren

Has anyone considered riveting the tank ribs dry as is done with the outboard leading edge, and then prosealing a good quality fillet around the perimeter of the ribs and encapsulate the rivet shop heads? The baffle would then be installed as normal per the plans.