MEK does not cause blisters.....

[David-aviator]

Would a moderator please delete the entire thread "Hypothesis...." on paint blisters. The theory that MEK changes the chemistry of the sealant is in total error. Thank you, David Edgemon.

David Edgemon wrote:

I've built 2 RV's. Thats 4 tanks, with no, Thats NO blisters. The first plane, 9A was completed in 2004, 500 + hours and NO blisters.

What does that have to do with MEk, I thinned every batch with MEK during application (I know, my airplane is going to explode).

I also painted the thinned sealant onto all of the rivet tails so that they are fully encapsulated.

So I would humbly suggest that you look T your selant application technique, not your paint prep.

Further evidence that this is true lies with the clean up paper towels I used yesterday after building a test strip. They were soaked in MEK, the sealant on them cured over night. It's properties are essentially unchanged, at least visually and as far as I can tell.

Again, thanks dedgemon for sharing your knowledge and experience on this matter.

[David-aviator]

Some people refuse to accept that it is nothing more than poor workmanship in proseal application technique that causes paint blisters to develop. The blisters develop because fuel or its fumes migrate though an improperly prepared barrier of proseal when the fuel tanks are constructed. Gimmicks like Locktite are nothing more than a bandaid fix that address a problem that should never arise in the first place. Slight pressurization occurs in properly constructed fuel tanks and I find it curious and vindicating that if second hand reports are to be believed, even Van's seems to be grudgingly coming around to accept what I have insisted from day one in multiple posts on the famous paint blister thread started nearly 6 years ago:

http://www.vansairforce.com/communit...=paint+blister

And I would remind those doubters that even the pros can sometimes get it wrong as post #100 in that thread so graphically demonstrates:

http://www.vansairforce.com/communit...&postcount=100

Properly constructed fuel tanks using industry accepted proseal application techniques will not blister the paint and that inconvenient truth is for some RV builders a difficult pill to swallow.
__________________
Rick Galati
RV6A N307R"Darla!"
RV-8 N308R "LuLu"
EAA Technical Counselor

[noelf]

As another data point: Years ago when I built my tanks, I threw my ProSeal covered clecos into a clean paint can half full of MEK. At the end of the build session, I pounded on the cover to the can with the intention of cleaning the clecos a little later. Well, I forgot all about the can until some number of weeks later. When I eventually opened the can up, I found the proseal had cured on the submerged clecos. Interesting!!

[David-aviator]

Originally Posted by noelf

As another data point: Years ago when I built my tanks, I threw my ProSeal covered clecos into a clean paint can half full of MEK. At the end of the build session, I pounded on the cover to the can with the intention of cleaning the clecos a little later. Well, I forgot all about the can until some number of weeks later. When I eventually opened the can up, I found the proseal had cured on the submerged clecos. Interesting!!

Interesting, indeed.

I wonder if there is a difference in how ProSeal and ACETONE work.

Last week I dropped a couple sealant gunked-up rivet sets pieces into some ACETONE over night and by golly they were clean the next morning. It was an open can and the ACETONE had evaporated over night......maybe I imagined the event....some days I am amazed at how much I don't know?!

[rvbuilder2002]

I am familiar with one instance... an RV-10 Q.B. kit that had been completed by a professional hired gun builder.
Blisters developed on the fuel tanks.
Entirely new fuel tanks were built by a well respected builder who specializes in assembling RV fuel tanks.
The new tanks were installed and then painted by the professional painter that had originally painted the airplane.

8 months later... fuel tank blisters on the new fuel tanks.

So, in at least this one case, blisters occurred on fuel tanks built at totally different times, by totally different people, likely using at least slightly different processes. The only common factor was the painter and the paint products/process used.

I do not mean to imply that I think it is always the paint processes fault, but what I do think, is that there is not one single cause.
I think that of all of the instances where people have experienced this problem, that it has happened for a variety of different reasons. If I am correct, it explains why it has been hard to pin down and find a way to prevent it from happening.

There have been lots of opinions presented, that lean towards the assembly technique and proper application of sealant being the cause.
Personally, I think it is something else (though I don't know what) causing it.
The reason I feel that way is this...
I have been involved in the construction of RV's for 24+ years. Other people had been building RV's long before I got involved. For the most part, all of these people were amateurs, with no special training in aircraft construction. They new nothing about Mil Spec processes for doing sealant application etc., but they have built thousands of airplanes, that have been flying for many years and have never had a tank blister (other than were an obvious leak occurred at a rivet).
It is only within the past few years that this has begun to occur (though still only a small percentage of the recently completed airplanes have experienced this)

So what then is the cause? I don't know, but I am convinced that if we do ever discover the cause, it wont be a single smoking gun that we can blame on all the occurrences of the blister problem.

[Mike S]

Originally Posted by David-aviator

Would a moderator please delete the entire thread "Hypothesis...." on paint blisters.

Took care of that for you.

[Mike S]

Originally Posted by rvbuilder2002

So, in at least this one case, blisters occurred on fuel tanks built at totally different times, by totally different people, likely using at least slightly different processes. The only common factor was the painter and the paint products/process used.

Scott, this is interesting new info.

I wonder if there is any time frame correlation with EPA mandated changes in paint formulas ???

Could all of us been barking up the wrong tree?

[JDanno]

So what do you do about leaky fuel tanks that Van's contractors made?? You can't get inside and patching the outside is sketchy at best.
Arrrggg!

[rvbuilder2002]

Originally Posted by Mike S

I wonder if there is any time frame correlation with EPA mandated changes in paint formulas ???

I feel pretty certain that this is the cause of at lease some of the instances of blisters (but I have no strong evidence to prove that).
I do know that a lot has changed in the formulation of paints.
I have seen paints being marketed under a popular trade name, and having been popular with home builders for many years for painting their RV's, (paints that weren't specifically marketed for use on aircraft) suddenly have an obvious change in susceptibility to staining from dye in 100LL, 5606, etc.

I know that a lot of the instances of blisters have been the paint delaminating from the primer undercoat, but the primer still having good adhesion to the rivet area.
What does this mean. I don't know for sure, but to me it indicates that the crosslinking process between the primer and paint has failed to happen properly.
I don't know what the cause is, but one could be the strict requirements the paint manufacturers have regarding maximum cure time limit of the primer before it gets top coated. Some are less than 24 hours. (BTW, this one issue by it self shows that it is a bad practice (and a waste of time and money), to prime the exterior of parts during the building process. For good paint adhesion, you would need to re-prime all of those surfaces with fresh primer just before painting.

[DanH]

Originally Posted by JDanno

So what do you do about leaky fuel tanks that Van's contractors made?? You can't get inside and patching the outside is sketchy at best. Arrrggg!

Yes, you can get inside. You cut a 5" round hole in the rear wall of each bay and close it later with a 6.5" cover plate, closed-end blind rivets, and sealant. You can reach everything and seal everywhere. In one respect it is better than building new tanks; it allows the installation of a proper fillet along the skin/rear wall joint.