What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Paint Blisters/Fuel Tank Rivets

RV8 Blisters

My RV8 also has QB tanks. I first flew it Sep. 19 2008 so it is less than a year old. I have at least 30 paint blisters top and bottom on each tank. I know that if all tanks don't have this problem, it is (positively a quality control issue). I feel that if I built the tanks I would not have this problem. I do want to build new tanks myself instead of trying to repair the mess an unskilled foreign worker did. I have looked inside and all around these tanks and truly believe I could coach my 11 yr. old son through a tank build and get much better results. I don't want any compensation from Van's but do believe it would be right for them to supply the tank kits free of charge or at least at a substantially reduced rate. I have already lost the time of painting this junk set of tanks and now have to do it again. Has anyone with QB tanks been able to work such a deal with Van's? I would gladly ship them my tanks back for a trade for new tank kits.
 
Hey Rick,

Do you have any pictures backing up your theory? :)

Van's expressed a possible cause to the problem sometime ago.

They assert there is a form of corrosion going on at ALL rivet heads with some airplanes due to an unknown issue with cleaning, prepping, priming and/or painting the airplane. A gas is forming at the rivet/skin joint and it has to go somewhere. If the rivet is pro sealed, it lifts the paint. If it is not pro sealed, the gas escapes around the rivet shank and does not lift the paint.

That theory fits the evidence. But there is no clew as to what is causing the gas to form.

For sure the blisters are associated with pro seal. And we could rule out fuel because there is no fuel at the aft bulkhead outside flange.

So, what's left?
 
.......we could rule out fuel because there is no fuel at the aft bulkhead outside flange.....
David,

I do not rule out fuel as the likely agent acting to promote paint blisters. You dismiss fuel as the cause by asserting "there is no fuel at the aft bulkhead outside flange." Well I have to disagree with that line of reasoning on two levels. First and most obvious, the paint blistering is reported to occur ONLY on fuel tanks, not the wing, not the flaps, not the fuselage. Second, the aft bulkhead outside flange you refer to is part of a closed vessel that contains fuel...and sometimes the fuel contained within that closed vessel is under slight pressure. If through improper assembly a void exists in the proseal boundary that is supposed to exist between the skin and the aft bulkhead outside flange from the inside of the tank, fuel or its fumes will certainly find that void and proceed to seep between the skin and rear baffle flange through that void and continue its migration through and out a rivet hole, especially a poorly prepared rivet hole. The only thing unique to that "aft bulkhead outside flange" is that it sits at a right angle to all the other "flanges" internal to the fuel tank (ribs, stiffeners) but fuel is still in contact with it, even if only making contact from one inside. That is why Van's emphasizes and directs the standard kit builder that in addition to properly sealing the faying surfaces, a good bead of proseal should applied along the entire INSIDE length of that rear baffle area to act as a dam of sorts because it is helpful in keeping fuel contained and where it belongs. Are you sure your quickbuild tanks were built with that attention to detail? Given that you stated in a prior post you observed no shop rivet head encapsulation when peering inside your quickbuild fuel tanks, I kinda doubt it.

dhet6e.jpg


When you think about it, properly applied proseal provides THREE barriers of protection against fuel leakage. 1. Under the rivet head 2. Between the sheets (faying surfaces). 3. Rivet shop head encapsulation. Omitting any one of these three levels of protection increase the chance that fuel can and will find a way out of the tank through the skin either at a rivet location or between parts.

Now lets take a good long look at these cleated rivets: If ANY rivets of this dubious quality exist inside the fuel tank and even worse, not properly encapsulated, it is not very hard to imagine how fuel can seep through a side of the hole and exit the fuel tank from under that rivet's manufactured head and leaving its telltale 100 LL blue dye calling card streaking all over your pretty little paint job. Without proseal blocking the path what's to keep the fuel inside?

2u53tb4.jpg
 
Last edited:
Many builders are flying with trailing edges that were prosealed when assembled to assist in keeping them nice and straight. Has anyone reported paint blisters from those rivets? If not, I have to discount the proseal theory and stick with the fuel theory.
 
I had the blister problem on my RV-10. As luck would have it, I now have the same problem on my RV-7A. The common thing is that the tanks are the same vintage--- QB around 2004/2005. I even took extra care in prepping the 7 tanks for paint, since I had the problem on the 10. The only areas we have this problem are on the fuel tanks. No where else on the airplane. It is definitely some combination of fuel and paint and proseal (or lack thereof). The tanks on the 7 are looking pretty bad. :(

Vic
 
Rick, How would you rate this example? Positives? Negatives? Thanks! -Jim
Jim,

It is difficult if not impossible for me to render an informed opinion lacking an up close and personal examination and based solely upon a photograph but I can offer you my general thoughts on the subject. There are 2 things I look for and consider absolutely mandatory in fuel tank construction. #1. The rib or stiffener is completely surrounded by an unbroken filet seal. #2. The shop heads of the rivets are fully encapsulated. For illustration, here is an example of a pair of stiffeners in the interior of a set of my own fuel tanks:

2n242g8.jpg


If you are assured the rib in your photograph meets the two criteria I outlined above and all surfaces have been sufficiently prepared and cleaned, the chances are excellent you are building a leak free fuel tank.

2qvw9wx.jpg


As the above photo shows, I prefer to completely fill in flutes generated in the rib straightening process. Doing so helps provide the basis for forming an uninterrupted filet seal less likely to contain any hidden voids and completely surrounds the rib with proseal when the rib is clecoed into place.
 
David,

.....Are you sure your quickbuild tanks were built with that attention to detail? Given that you stated in a prior post you observed no shop rivet head encapsulation when peering inside your quickbuild fuel tanks, I kinda doubt it....

I do not know the level of attention given the construction of my tanks built in 2001-2002. The inspection of the interior was with a flash light peering in through the fuel cap hole. I believe what was reported was that some of the shop heads were not encapsulated.

We do know the blisters are occurring where pro seal is present and no where else. Fuel and fumes may be present at the aft flange. That is where the blisters appeared first for me. I also have blisters on top of the tank where fuel fumes are present but actual fuel very seldom. With open fuel vents, it is difficult to image enough pressure within the tank to force fumes up and around a rivet shank and lift the paint.

There is no question if one builds fuel tanks as you have and many more applications at your place of work, they will not leak. I've seen both of your airplanes and they are of the highest quality through out as is your POH. But I must point out, as I recall, neither machine has paint on the wings.

If your wings were painted and the blisters did occur, what would your thinking on the subject be?
 
If your wings were painted and the blisters did occur, what would your thinking on the subject be?
Dave,

I feel no need to engage in "What if's."

You say that blisters are occuring where proseal is present and nowhere else. Well, you could also say blisters are occurring where FUEL is present and nowhere else and be just as accurate.

The fact is that thousands of airplanes are flying without fuel tank blisters. It seems only a tiny minority display the problem with paint blistering/lifting as yours does. And within that tiny minority of builders reporting such problems, quickbuild fuel tanks seem to occupy front row status. Did you take a look at the level of quality I documented in the quickbuild photos a few posts back? Now I wish I could offer you a silver bullet. I have stated over and over again that quickbuild tanks I have observed are NOT assembled the same way the builders manual clearly directs the standard kit builder to do things. Missing proseal is missing proseal. Defective rivets...MULTIPLE defective rivets are still defective rivets. Are these examples what some people call "good enough?" You can continue to deny that fuel has anything to do with this issue, that is your privilege. I happen to see it as front and center. Fuel must be kept contained using the proper application of proseal. If it is not, in one way or another that fuel will surely have its way with almost any paint.

Finally, proseal is not only compatable with paint but also happens to be highly paintable. Raw exposed proseal is routinely painted over on hundreds of thousands of aircraft the world over with no ill effect. Proseal naturally resists the effects of fuel in a way that most paint products were never designed to do.
 
Last edited:
Add another one

Blisters on my 7A quickbuild. Mostly on the passenger side top of tank but some on bottom. Plane was painted with epoxy primer and house of color top coat/clearcoat. Took about 6 months to show up. Has anybody successfully repainted the tank and no longer had the bubbles?
 
Mine are getting much worse!

Hi Dan,
You observed my blisters first hand at Rhodes Flyin. I have not personally cut into them yet but I run mostly mogas and have yellow streaking coming from them, common with mogas leakage. There are probably twice as many as you saw earlier in the year. No joy with the mothership as it is always the consumers fault. I knew I should have torn those new QB tanks apart and rebuilt them right, who would'a knew. Still trying to get mothership to help me out. :(
 
So now what....

I have an RV8 QB about one year out of the paint shop. The first blisters appeared within a month of painting only on top of the tanks. Especially this past summer MANY more appeared both top and bottom--tank only. There are now probably 75 or 80 blisters between the 2 tanks.

There is no fuel grossly visible upon rupture.

I would like to start moving toward repairing this....is there any semblance of consensus on what to do? Other than build new tanks.....
 
Blisters on my 7A quickbuild. Mostly on the passenger side top of tank but some on bottom. Plane was painted with epoxy primer and house of color top coat/clearcoat. Took about 6 months to show up. Has anybody successfully repainted the tank and no longer had the bubbles?
This is scary. I had one rivet blister on the top of my right slow build RV-7 tank. My paint is the complete House of Kolor system from Epoxy primer up through the white base coat, pearl stripe and clear top coat. Happened a couple of weeks after I started flying. The right tank had other problems with weeping rivets on the bottom. Haven't had any problems after fixing the weepers and repainting the tank. All I did on the one with the blister was sand it down, prime and repaint. Now have about 60 hours on the plane and all is holding with no weepers or blisters.
 
I have an RV8 QB about one year out of the paint shop. The first blisters appeared within a month of painting only on top of the tanks. Especially this past summer MANY more appeared both top and bottom--tank only. There are now probably 75 or 80 blisters between the 2 tanks.

There is no fuel grossly visible upon rupture.

I would like to start moving toward repairing this....is there any semblance of consensus on what to do? Other than build new tanks.....

Don't know what the next step is other than ordering a $800.00 tank kit and rebuild them yourself correctly. I do know that if I were to do it again, I would not include the QB tanks with my purchase or recommend anyone else to do it either. Wander if you can get QB wings without the tanks assembled?
 
Last edited:
Loctite or other external sealer??

New tanks? Ahrgghhhhhh....not what anyone wants to hear.......

We sent a guy to the moon and back 40 years ago....surely there is some sealer out there that can be applied externally and painted over that will solve this???

Somewhere there was talk of using loctite red--or was it blue---whatever!!??

suggestions????
 
N147RV Paint Blisters

Here's the lowdown on my airplane. First flight was Sep. 19, 2008. Wings were painted about three months prior to first flight with no imperfections detected. I started seeing blisters within a month after adding fuel and steadily got worse as warm weather set in. Now I have approximately 75-100 blisters on both tanks top and bottom combined. Most are on the back baffle where I realize it's much more difficult to get a good filet of proseal. I was told by mothership that it was the way it was prepped before painting because all the solvents used to clean the wing was not allowed to evaporate properly. I was also told also by MS that I would not have this problem with the inner ribs because a proper filet could be applied here. Well now I have about as many on the inner ribs as the back baffle. I read about the problems before painting. I painted this plane myself and took the precautions I read on this site before applying paint. The only solvent introduced to my tanks before painting was the PPG DP48 epoxy primer. I used all PPG products (primer, dbu basecoat, ppg global clear). This is an extremely slick paint job. Now the tanks ruin the appearance and clearly must be redone. I have painted many planes in the past with this very process including several spamcans and never had this problem. I'm not a professional painter but have turned out several award winning planes as Dan Horton can attest. Here's some photos of my tanks. Maybe MS will come to realize they have a QC problem with their tank builders. Hopefully soon because this is going to be an expensive ordeal that I or any other QB purchaser should not have to bear. I'm not trying to product bash at all, just wanting MS to step up and do the right thing. The last photo is a borescope shot of visible rivets without proseal.
IMG00036-20090805-1450.JPG
[/IMG]
IMG00034-20090805-1449.JPG
IMG00038-20090805-1451.JPG
IMG00037-20090805-1450.JPG
IMG00039-20090805-1451.JPG
IMG00040-20090805-1451.JPG
IMG00042-20090805-1452.JPG
IMG00046-20090805-1455.JPG
 
Hi Dan,
You observed my blisters first hand at Rhodes Flyin.(

Yep, I saw 'em, top and bottom, ruining a perfectly lovely paint job. And now they're worse.

This is an unacceptable situation.

Ok, let's humor Vans for a moment. Bill, walk us through your entire paint prep process. Exactly what prep did you do prior to shooting DPLF?
 
Last edited:
Has anyone tried sealing from the outside? Some resin and dime size fiberglass rounds over the tank rivet heads.
 
Repairing

The only feasible way of making a repair would be to cut access holes in the rear baffle between each rib, scrape the offending sealer out best you can, then reapply proseal properly. I don't know if one could truly get to all the troublesome places without removing rivets and resealing.:mad:
 
Prep

This is an unacceptable situation.

Ok, let's humor Vans for a moment. Bill, walk us through your entire paint prep process. Exactly what prep did you do prior to shooting DPLF?

Dan,
I used scotchbrite pads (maroon) and dawn dish detergent with a firm scrubbing for tooth adhesion for the paint. I guess some QB'ers get lucky and don't have this problem but don't fool yourself into thinking there's not a problem.
 
I was told by mothership that it was the way it was prepped before painting because all the solvents used to clean the wing was not allowed to evaporate properly.

If, as Vans claims, it was just a matter of solvents being trapped then why would the problem be restricted to the fuel tanks. Can this make any sense.:confused:

Rick Galati's previous astute observations and comments on this thread about the problems with rivet shop heads not being encapsulated will ultimately be proven to be correct.

QB builders have variously reported in the past that some Vans fuel tanks have encapsulation of the rivet shop heads and some do not. That is a fact.

My best guess is that the Philippines subcontractor is fabricating these tanks to the same instructions that slow build builders receive in their construction manual. I cannot see why a subcontractor and a builder would receive different instructions to build the same fuel tank.

My Van's tank construction instructions specifically say: "Dab a bit of sealant over every rivet head". To me this clearly says ENCAPSULATE THE RIVET SHOP HEAD WITH PROSEAL.

I think we can safely assume from this that in some instances the subcontractor is not following Vans instructions consistently in this regard. I think we can also safely assume that Vans has not been checking the tanks internally (at least not in the past) to see whether their instructions are being followed.

The fact that some QB tanks have encapsulated shop heads and some do not is clear proof that there has been a breakdown in quality control procedures in terms of tank construction. For those with blisters developing under their very expensive paintwork that is a disaster.
 
Last edited:
If, as Vans claims, it was just a matter of solvents being trapped then why would the problem be restricted to the fuel tanks. Can this make any sense.:confused:

Rick Galati's previous astute observations and comments on this thread about the problems with rivet shop heads not being encapsulated will ultimately be proven to be correct.

QB builders have variously reported in the past that some Vans fuel tanks have encapsulation of the rivet shop heads and some do not. That is a fact.

My best guess is that the Philippines subcontractor is fabricating these tanks to the same instructions that slow build builders receive in their construction manual. I cannot see why a subcontractor and a builder would receive different instructions to build the same fuel tank.

My Van's tank construction instructions specifically say: "Dab a bit of sealant over every rivet head". To me this clearly says ENCAPSULATE THE RIVET SHOP HEAD WITH PROSEAL.

I think we can safely assume from this that in some instances the subcontractor is not following Vans instructions consistently in this regard. I think we can also safely assume that Vans has not been checking the tanks internally (at least not in the past) to see whether their instructions are being followed.

The fact that some QB tanks have encapsulated shop heads and some do not is clear proof that there has been a breakdown in quality control procedures in terms of tank construction. For those with blisters developing under their very expensive paintwork that is a disaster.

The evidence seems to point to exposed shop heads, but I still have not accepted Rick's theory on why so many blisters are occurring at the aft bulkhead rivets which are outside of the fuel tank. Most of mine are in the line of rivets exposed to air top and bottom, not exposed to fuel.

Beyond all that, I would like to build a new set of tanks but that too poses a problem - match drilling the Z brackets to the spar sheer web. Normally, that is done before the bottom wing skin as closed out. I am still in the discovery phase of determining if it can be done.
 
Dan,
I used scotchbrite pads (maroon) and dawn dish detergent with a firm scrubbing for tooth adhesion for the paint.

Thanks Bill. The "unevaporated prep solvent in the rivets" theory makes no practical sense for several reasons. However, we need data and yours is valuable.

Anyone believe dish detergent and water can generate a chemical reaction when applied to a prosealed rivet?

Let's get behind Andy's proposal to gather an information database.
 
....why so many blisters are occurring at the aft bulkhead rivets which are outside of the fuel tank. Most of mine are in the line of rivets exposed to air top and bottom, not exposed to fuel.

Beyond all that, I would like to build a new set of tanks but that too poses a problem - match drilling the Z brackets to the spar sheer web. Normally, that is done before the bottom wing skin as closed out. I am still in the discovery phase of determining if it can be done.
Dave,

Oh but those rivets ARE (potentially) exposed to fuel! Without a proper fay and filet seal to otherwise block the path, fuel or fumes can seep between the bulkhead flange and skin and then up and out a rivet hole.

As for match drilling the Z brackets...of course it can be done:

http://www.vansairforce.com/community/showthread.php?t=11999&highlight=transfer+punch
 
Dave,

Oh but those rivets ARE (potentially) exposed to fuel! Without a proper fay and filet seal to otherwise block the path, fuel or fumes can seep between the bulkhead flange and skin and then up and out a rivet hole.

As for match drilling the Z brackets...of course it can be done:

http://www.vansairforce.com/community/showthread.php?t=11999&highlight=transfer+punch

Thanks for the tip on drilling those brackets to the existing spar sheer web holes. It is not so much the drilling as getting an angle drill into the area through the access covers from the bottom of the wing. I am still in the process of reading the drawings on building the tanks to figure it all out.

Kent Scott did not know of anyone ever doing it to this point, but someone out there probably has. There have been many RV's rebuilt for one reason or another.
 
Again....any outside seal solution???

Seems like the cause is likely known-at least likely enough for my curiosity.

The big question now is: What can be applied externally and painted over to solve this--if anything??

Somewhere there was mention of Loctite??

FWIW: My wings look almost identical to the blue pics above.
 
Tank baffle rivets and encapsulation, trapped solvents

Rick has been very insistent about the importance of fully encapsulating the shop tail of each rivet.

But many of the rivets that are forming blisters are on the upper rear row of rivets that hold the rear tank baffle on. I pointed out early in this thread that for those rivets, it would not matter whether they were encapsulated or not, because the tail is not in the propogation path of fuel vapor through the proseal. This point was ignored/dismissed. So, here I have made a picture:

rivet_proseal.jpg


From this picture you can see why I do not understand how it would matter one way or another whether the shop tail of this rivet was encapsulated. It is not in the fuel propogation path. So, personally, I think the issue of encapsulating the rivet tails is being over-emphasized. It is no doubt a good idea on the interior rivets, but it can not matter for the baffle rivets, it seems to me.

One push-back on Van's assertion that solvents and prep materials are trapped around the tank rivets and can not breath down through the rivet to escape like other rivets: If this were the problem, why have many experienced painters that do many other airplanes only seem to have problems with quickbuild tanks from Vans? They use the same process on other airplanes with prosealed tanks with no problem. And why only quickbuild tanks? So I'm afraid that assertion doesn't hold up.
 
solvent

Dan,
I think it would be the solvent that you wipe things down with after the dish detergent. Some guys use pretty strong stuff (acetone, etc...) that might soften the pro-seal around the rivet for a bit.

Maybe its time to rivet up some test panels and collect some real data?

Hopefully you guys will detect some common thread in the database!



Thanks Bill. The "unevaporated prep solvent in the rivets" theory makes no practical sense for several reasons. However, we need data and yours is valuable.

Anyone believe dish detergent and water can generate a chemical reaction when applied to a prosealed rivet?

Let's get behind Andy's proposal to gather an information database.
 
External sealant experiment

I have done an experiment for the possibility that an external sealant over the tank rivets might help. I have QB tanks on my -8, built in early 2007. Before paint, I washed the wings with acetone, and applied a drop of green Loctite on each rivet head. I did not use any internal suction, just relied on any natural wicking action.

I have no idea whether this will help, it was just something to try. A little bit of internal vacuum would have been smart, but I didn't have time in the midst of paint prep.

The wings have been painted for about a year, and the tanks have now had fuel in them for about a month. It sounds like blisters often show up at around 6 months, so, we shall see.

Like nuclear deterrants, there is no way to know for sure if this works, we will only no for sure if it doesn't work. ( I.E. If I don't get blisters, its hard to say for sure that it was because of the Loctite)
 
....many of the rivets that are forming blisters are on the upper rear row
of rivets that hold the rear tank baffle on....I pointed out early in this thread that for those rivets,
it would not matter whether they were encapsulated or not...
I have also stressed the importance of a good fay/filet seal boundary. I have explained this before but your drawing provides
me with a convenient way to illustrate. If any voids exist in the fay/filet seal boundary because of poor application technique,
fuel or fuel fumes will surely find a way out of the fuel tank along that migration path. Passing a pressure test is one thing,
long term exposure to fuel and the naturally slight pressure that can occur within a fuel tank can reveal more subtle defects
at much later date. In any event, Van's does direct the builder to apply a good bead of sealer prior to inserting the rear baffle.
If this is not done correctly, the tank may not leak fluid in any obvious way, but over time the subtle effects of that fuel or
fumes in contact with paint may eventually cause a reaction. That is why I stress 3 key areas to pay particular attention to
when sealing a fuel tank. These are not difficult steps to achieve but they are necessary.

#1 Encapsulation. #2 Fay/filet seal. #3 Sealer under the manufactured head of the rivet.

I refer anyone to review post #100 on this thread. See for yourself what I found while peering INSIDE a QB fuel tank. Look at it
and then you tell me....is what you see in that particular photo...."good enough" for you? As far as I am concerned, to date
no other explanation offered thus far has a proven persuasive counter to my unchanged suspicions.

2lse808.jpg
 
Last edited:
Does anyone know what the % of QB vs std build is?

We do have many slow build guys like me with the blisters. I wonder how the install base compares to field failure rates(QBvStd)?

I do see a trend towards proseal from a common set of years. Dont know if thats a factor. Was there a single blister before 2002? Was there a single one after ~2007? I never heard of this before ~2005 or so. And certainly not before ~2000. Surely if the problem was application technique, which im not on board with at this point, we would have seen this in the 90's. Surely we would have.

This may have more to do with the internet and install base than actual failures.:confused:

Since the failure takes time to see, we cant get infancy mortality rates from the field data which can skew the view.
Im wondering out loud if there is any coorelation between QB failure rates and QB install base. I also wonder if a higher rate of QB builders come to this forum. I wonder I wonder. I dont know.

I liked the post with the bore scope. Couldnt see ....but I could easily enough take a few inside tank pictures of mine. I got blisters everywhere, except the rear baffle.

Also if there was some gaseous chemical thing going on, why then on mine after having blisters for years, then stripping the paint, and shooting it again, they come back? Surely this chemical reaction theory goes bunk after years of exposure and repainting.... they come back.

Im so confused.
 
Yes, I agree with this completely.

I have also stressed the importance of a good fay/filet seal boundary. I have explained this before
but your drawing provides me with a convenient way to illlustrate. If any voids exist in the fay/filet seal
boundary because of poor application technique, fuel or fuel fumes will surely find a way out of the fuel
tank along that migration route. Passing a pressure test is one thing...long term exposure to fuel and the
naturally slight pressure that can occur within a fuel tank can reveal more subtle defects at much later
date. In any event, Van's does direct the builder to apply a good bead of sealer prior to inserting the rear baffle.
If not done correctly, the tank may not leak fluid in any obvious way, but over time the subtle effects of that
fuel or fumes in contact with paint may eventually cause a reaction. That is why I stress 3 key areas to pay
particular attention to when sealing a fuel tank. These are not difficult goals to achieve but they are necessary.
#1 Encapsulation. #2 Fay/filet seal. #3 Sealer under the manufactured head of the rivet.

I refer anyone to review my observations of a pair of QB tanks shown in post #100. You tell me. Are they "good enough?"

2lse808.jpg

This point I fully agree with. When I had my right QB tank open for install of flop tube and float sensor in second bay, I looked at all the fillets and they looked pretty good. We'll see what happens to my tanks....
 
bubbles on tanks

i find this very interesting, i built a slow build rv-10 using epoxy self etchin primer and topcoated with acrylic enamel with a urethane hardener. the paint job on the entire aircrft was done with the same methods and materials and only the fuel tanks blistered with pinhead size blisters all over the tank not just around the rivets. the only difference between the tanks and the skins is that the tanks were messy with prosel which i then cleaned off with laquer thinner, acetone, mek and naptha basically whatever i had laying around. i'm sure residue of that sealant made its way all around the tank in the wiping off process. the tank was scotch brighted before painting. i want to say that i believe it must be the proseal residue. initially i thought i must have made a boo in prepping for both tanks only but the odds are against that. i'm gonna switch brands of proseal and solvent wipe more thouroughly next time (yes i said next time, i must be crazy)
 
i find this very interesting, i built a slow build rv-10 using epoxy self etchin primer and topcoated with acrylic enamel with a urethane hardener. the paint job on the entire aircrft was done with the same methods and materials and only the fuel tanks blistered with pinhead size blisters all over the tank not just around the rivets. the only difference between the tanks and the skins is that the tanks were messy with prosel which i then cleaned off with laquer thinner, acetone, mek and naptha basically whatever i had laying around. i'm sure residue of that sealant made its way all around the tank in the wiping off process. the tank was scotch brighted before painting. i want to say that i believe it must be the proseal residue. initially i thought i must have made a boo in prepping for both tanks only but the odds are against that. i'm gonna switch brands of proseal and solvent wipe more thouroughly next time (yes i said next time, i must be crazy)

Were your bubles all over the tank or just around the rivet heads? It seems that if it was the solvent wipe it would seem that the bubbles would be over more of the surface than the rivet heads...just curious...

Bob
 
I don't have any specific idea of what has caused this problem with a small percentage of RV tanks and I am not sure anyone ever will. The reason I believe this is I feel quite certain that the blisters have been caused by different problems on different airplanes.

Here are a few of the reasons I believe this.

- the problem has occurred on standard build and Q.B. fuel tanks

- the problem has occurred on Rv's painted with many different paint systems.

- The problem has occurred on RV's prepped with many different paint prep processes.


One thing I can tell you that I am certain is not the cause of paint blisters...
It is not whether all of the rivet heads were coated in proseal before the tank was closed.
BTW, as far as I know, the only reason that step is in teh construction manual is to give amateur builders every possible chance that they can get, of avoiding a leak.

In my 22 years of building RV's I have built about 15 sets of fuel tanks. I have never coated the rivet shop heads in any of the tanks I have built. I actually remove any sealant from within the dimples before inserting the rivets to make sure that they lay down flush with the the surface of the skin. When I rivet a tank, I am relying on the sealant squeezed around the rivet shank in the small space that is between the rib and the skin to make the seal.
I use about 1/2 of a quart can of sealant to build a standard set of two place RV fuel tanks.
I have never had a fuel leak or paint blister at any rivet on any tanks I have built to date.

I do have a couple of theory's of what has caused at least some of the rivet blisters on some tanks.

One is surface sanding - because of the sealant under rivet heads on the tank, often times there are rivets sticking up above the skin surface. This sometimes doesn't show how bad it is until a coat of primer is sprayed on. I believe some builders have block sanded over the rivet lines to improve the final finish. This removes primer from the high spots on the rivets. If paint is then sprayed, there are small areas on rivets where there is very poor paint adhesion. This coupled with the entrapped paint solvents around the perimeter of the rivet, sets up the opportunity for the solvents to expand and lift the paint into a blister. A strong piece of evidence for this is that there are many instances on different RV's where the only blisters on the tanks were along the line of rivets for the rear baffle flange. As was mentioned in a previous post, a properly installed baffle (one that is not leaking) does not have any fuel on the shop head side of the rivet. One thing that is different about these rivets though, is that they are machine countersunk holes instead of dimple countersunk. A machine countersunk hole is much more sensitive to rivet fit than a dimple countersunk one. Because of this, even the slightest amount of sealant under the rivet makes it look like it sticks up a lot. That makes these rivets much more likely to get some treatment with a sanding block just before shooting the paint.
Any painter will tell you that paint formulations have changed a huge amount in the last 10 - 15 years because of all the EPA regulations and removal of harmful compounds (like lead). Years ago, we could get away with doing this type of sanding treatment...the paint would still adhere great. Now a days the paints are much more sensitive to proper surface prep and proper use of primers for good adhesion.

Let me reemphasize that I don't mean to imply I think this is the cause of all of the paint blisters. I know that it is not, but I do believe it is the cause of some of them.

My primary point is that I do not think there is a single smoking gun cause and that I do not think anyone should be trying to lump all of the problem under one cause.
 
I don't have any specific idea of what has caused this problem with a small percentage of RV tanks and I am not sure anyone ever will. The reason I believe this is I feel quite certain that the blisters have been caused by different problems on different airplanes.

Here are a few of the reasons I believe this.

- the problem has occurred on standard build and Q.B. fuel tanks

- the problem has occurred on Rv's painted with many different paint systems.

- The problem has occurred on RV's prepped with many different paint prep processes.



One thing I can tell you that I am certain is not the cause of paint blisters...
It is not whether all of the rivet heads were coated in proseal before the tank was closed.
BTW, as far as I know, the only reason that step is in teh construction manual is to give amateur builders every possible chance that they can get, of avoiding a leak.

In my 22 years of building RV's I have built about 15 sets of fuel tanks. I have never coated the rivet shop heads in any of the tanks I have built. I actually remove any sealant from within the dimples before inserting the rivets to make sure that they lay down flush with the the surface of the skin. When I rivet a tank, I am relying on the sealant squeezed around the rivet shank in the small space that is between the rib and the skin to make the seal.
I use about 1/2 of a quart can of sealant to build a standard set of two place RV fuel tanks.
I have never had a fuel leak or paint blister at any rivet on any tanks I have built to date.

I do have a couple of theory's of what has caused at least some of the rivet blisters on some tanks.

One is surface sanding - because of the sealant under rivet heads on the tank, often times there are rivets sticking up above the skin surface. This sometimes doesn't show how bad it is until a coat of primer is sprayed on. I believe some builders have block sanded over the rivet lines to improve the final finish. This removes primer from the high spots on the rivets. If paint is then sprayed, there are small areas on rivets where there is very poor paint adhesion. This coupled with the entrapped paint solvents around the perimeter of the rivet, sets up the opportunity for the solvents to expand and lift the paint into a blister. A strong piece of evidence for this is that there are many instances on different RV's where the only blisters on the tanks were along the line of rivets for the rear baffle flange. As was mentioned in a previous post, a properly installed baffle (one that is not leaking) does not have any fuel on the shop head side of the rivet. One thing that is different about these rivets though, is that they are machine countersunk holes instead of dimple countersunk. A machine countersunk hole is much more sensitive to rivet fit than a dimple countersunk one. Because of this, even the slightest amount of sealant under the rivet makes it look like it sticks up a lot. That makes these rivets much more likely to get some treatment with a sanding block just before shooting the paint.
Any painter will tell you that paint formulations have changed a huge amount in the last 10 - 15 years because of all the EPA regulations and removal of harmful compounds (like lead). Years ago, we could get away with doing this type of sanding treatment...the paint would still adhere great. Now a days the paints are much more sensitive to proper surface prep and proper use of primers for good adhesion.

Let me reemphasize that I don't mean to imply I think this is the cause of all of the paint blisters. I know that it is not, but I do believe it is the cause of some of them.

My primary point is that I do not think there is a single smoking gun cause and that I do not think anyone should be trying to lump all of the problem under one cause.

If you could look inside my tanks you would clearly know the cause. Very poor workmanship. I looked directly at the rivets under the blisters with a borescope. No encapsulation with proseal. You had the luxury of knowing what had been done in the tanks you built. A QB builder does not.
 
If you could look inside my tanks you would clearly know the cause. Very poor workmanship. I looked directly at the rivets under the blisters with a borescope. No encapsulation with proseal. You had the luxury of knowing what had been done in the tanks you built. A QB builder does not.

Bill I am sorry about your problem but I guess you missed one of my points...

I have built more than a dozen sets of tanks and I have never covered a single rivet shop head with sealant. None of these tanks have ever had a leak or paint blister at a rivet.

I am very confident that your problem is not purely caused by the fact that you can see exposed rivet heads inside your tank.
 
Bill I am sorry about your problem but I guess you missed one of my points...

Here's my point. Had I built these tanks, I would accept my mistakes and pay whatever needed to remedy the problem. I had no control over this matter. If you bought a NEW car with a leaky tank and was told by the manufacturer it was your fault, you my friend would be in the same boat as I.
 
I had 3 rivets leaking fuel [could see a blue trail], and many blisters elsewhere. Also a leaking seam. This is obviously poor quality control at the metalcrafters factory.
I have removed and fixed a few times already.
My next RV will be a quickbuild with slowbuild tanks.
 
......I have built more than a dozen sets of tanks and I have never covered a single rivet shop head with sealant. None of these tanks have ever had a leak or paint blister at a rivet.

I am very confident that your problem is not purely caused by the fact that you can see exposed rivet heads inside your tank.
I have no reason to doubt your leak proof success record after building more than a dozen fuel tanks. Success does speak for itself and I happen to completely agree with you in that I too do not think there is a single smoking gun cause and no one should be trying to lump all of the problems under one cause.

This comment really draws my attention though: "BTW, as far as I know, the only reason that step is in the construction manual is to give amateur builders every possible chance that they can get, of avoiding a leak." The tone conveys the "message" that even though the builders manual points clearly directs, a dab of sealer (on the rivet shop head) is (in your estimation) really not all that necessary. C'mon. What else in your estimation is contained within the construction manual we may be free to downplay as not all that necessary?

I think of the proper application of sealant as a three legged stool. #1. Shop head encapsulation. #2 Filet/fay seal. #3 Sealer under manufactured head of the rivet. Since, as you say you did not encapsulate any rivet shop heads and the reason why no problem has yet to crop up may well lie in the fact that the filet seal and wet installation of the rivets has so far proved to be a sufficient barrier to leak/fume proof the tank.

I do know that when mating surfaces are fay sealed and then rivets are shot while the sealer is still very wet, the squeeze out of sealer is so dramatic from around the sheets that what really remains is a very thin layer of sealer. If you could somehow separate the sheets, that sealer barrier is so thin and translucent you can literally see through it. That is why I personally prefer, besides being a much cleaner and easier way to build the tanks is to allow cleco button spring pressure alone be in place for a time while the sealer partially cures.

In any event, to get back to and reemphasize my point about a proper filet seal, I cannot accept this QB example lacking a filet seal as anywhere near meeting my personal standards of acceptability. By way of analogy, no filet seal and no shop head encapsulation effectively eliminated two legs from that 3-legged stool.

3535svt.jpg



This may or may not be an additional issue, but from what I can tell no surface preparation is apparent immediately adjacent to the stiffener as if the stiffener was installed on the alclad skin without any prior "roughing up" of the mating surface necessary to provide the proseal with enhanced gripping power. As you know, surface prep is an extremely important step and may or may not have been omitted in this specific case. I do however, freely concede my suspicion *may* be unwarranted so I'll give the benefit of doubt on this one.

HOWEVER, and this point is clearly undeniable...this QB fuel tank stiffener example is obviously devoid of any filet seal surrounding it. If any voids (migration path) happen to exist and hidden within the fay sealed surface between the stiffener and skin...no amount of rivet shop head encapsulation in the world will be of much help in preventing leaks.
 
Last edited:
One thing I can tell you that I am certain is not the cause of paint blisters...
It is not whether all of the rivet heads were coated in proseal before the tank was closed.

Scott, I have been following this thread, and others on this topic, with considerable interest for some time. To date literally dozens of builders have reported blisters. In all of the blister cases reported for both QB and SB tanks (except for one) the common denominator has consistently been a lack of shop head encapsulation. One person reported blisters and claimed he had shop head encapsulation...but when he was asked to provide further details he evaporated and did not reply. So the statistics to date strongly point to the fact that shop head encapsulation (or lack thereof) is a crucial factor.

BTW, as far as I know, the only reason that step is in teh construction manual is to give amateur builders every possible chance that they can get, of avoiding a leak.

I am at a bit of a loss over this statement. Surely if encapsulation "gives amateur builders every possible chance that they can get of avoiding a leak" then the same must apply to professional builders.

I would like to know why some tanks come out of the Philippines with encapsulation while others do not. What is Vans specific requirement of its subcontractor in that regard? Do Vans require encapsulation of the QB tanks or do they not? And if they do require encapsulation then why are some tanks getting through with no encapsulation? In the final analysis one would suspect that inconsistencies in the protocol of QB tank construction are an indication of ambiguous construction specifications and less than satisfactory quality control.
 
In any event, to get back to and reemphasize my point about a proper filet seal, I cannot accept this QB example lacking a filet seal as anywhere near meeting my personal standards of acceptability. By way of analogy, no filet seal and no shop head encapsulation effectively eliminated two legs from that 3-legged stool.

This may or may not be an additional issue, but from what I can tell no surface preparation is apparent immediately adjacent to the stiffener as if the stiffener was installed on the alclad skin without any prior "roughing up" of the mating surface necessary to provide the proseal with enhanced gripping power. As you know, surface prep is an extremely important step and may or may not have been omitted in this specific case. I do however, freely concede my suspicion *may* be unwarranted so I'll give the benefit of doubt on this one.

HOWEVER, and this point is clearly undeniable...this QB fuel tank stiffener example is obviously devoid of any filet seal surrounding it. If any voids (migration path) happen to exist and hidden within the fay sealed surface between the stiffener and skin...no amount of rivet shop head encapsulation in the world will be of much help in preventing leaks.

Rick,
I fully understand all of the points you make above but as you said your self in the above quote. These are your standards. I am not saying their is anything wrong with them. In fact they are good standards for builders to follow to help minimize the chance of any leaks.

Where I disagree is the implication that because you have seen Q.B. tanks that obviously do not meet your standards, that that is the reason for paint blisters happening on RV tanks.

The tone conveys the "message" that even though the builders manual points clearly directs, a dab of sealer (on the rivet shop head) is (in your estimation) really not all that necessary. C'mon. What else in your estimation is contained within the construction manual we may be free to downplay as not all that necessary?

I feel that this comment is kind of hitting below the belt. You seem to have looked right passed the point I was making... that I have built many tanks without meeting this part of your standard, and I have seen inside many many others that other builders have assembled without covering the rivet heads, (we could probably say many hundreds have been built this way, but I can't provide a specfic #) and none of them have ever had any leaks or paint blisters.

The main consideration for me reminds me of an old T.V. program.

The facts ma'am, just the facts.

I have seen lots of speculation but very little facts.
In fact I have seen no facts at all that substantiate that if a tank doesn't meet your standards that it is a total explanation for the paint blister problem.

In fact I think the evidence implies just the opposite. With as many tanks as have been built (leak and blister free) without being finished anywhere close to your standards, I think it is actually stronger evidence that the existence of paint blisters has no direct correlation with whether the rivet shop heads were sealed over. I don't mean to imply that it is not possible that some of them could have been prevent by doing so.

I am the first to admit that I need much more hard evidence and detailed information to make a determination of what the cause or causes are.

This same rule applies to all of the opinions that have been presented.

In my mind, it likes to a jury that just wants to make sure someone hangs for the crime, but has not concern whether the real criminal is still walking around free.
 
Scott, I have been following this thread, and others on this topic, with considerable interest for some time. To date literally dozens of builders have reported blisters. In all of the blister cases reported for both QB and SB tanks (except for one) the common denominator has consistently been a lack of shop head encapsulation. One person reported blisters and claimed he had shop head encapsulation...but when he was asked to provide further details he evaporated and did not reply. So the statistics to date strongly point to the fact that shop head encapsulation (or lack thereof) is a crucial factor.

As I already mentioned in my response to Rick... If anything, the evidence of no leaks or paint blisters in the hundreds of tanks that have been built without rivet encapsulation is evidence for just the opposite.
Quick build kits have been available for RV's since about 1994 (15 years). I have seen teh inside of many of those tanks over the years and can tell you that they didn't just stop encapsulating rivets in the last couple of years of production.

If not, then why does this problem seem to have just started up in the last couple of years?

This is the type of question we need to answer.



I am at a bit of a loss over this statement. Surely if encapsulation "gives amateur builders every possible chance that they can get of avoiding a leak" then the same must apply to professional builders.

I would like to know why some tanks come out of the Philippines with encapsulation while others do not. What is Vans specific requirement of its subcontractor in that regard? Do Vans require encapsulation of the QB tanks or do they not? And if they do require encapsulation then why are some tanks getting through with no encapsulation? In the final analysis one would suspect that inconsistencies in the protocol of QB tank construction are an indication of ambiguous construction specifications and less than satisfactory quality control.

These are questions for you to ask someone of authority at Van's. My opinion is that they are pointless questions until there is any real documented evidence that only RV tanks without encapsulation have paint blisters and those with encapsulation do not. I have seen or heard nothing to make me think that evidence exists.

Please don't get the wrong idea...I am curious about the cause and as interested in resolving it as anyone else, but speculating about the cause is not going to do that.
 
Call me skeptical

I built a standard kit and have been flying for 2 years, 2 months and so far no blisters.

I am however hesitant to place the blame on the QB factory if for only the following fact: The problem seems to be a lot of rivets blistering or no blistering at all. We seem to have tanks with many blisters or tanks with no blisters. To me this is inconsistent with placing the blame on weeping rivets.

Given the number of rivets in a pair of tanks and the fact that most tanks are built by first-timers, it is highly probable (approaching the point of certainty) that each pair of tanks has at least one rivet that is not sealed perfectly. Therefore if the blisters are caused by a bad seal in the tank, it stands to reason that a large number of customer-built tanks would exhibit the behavior with a limited number of blisters -- and that simply isn't the case.
 
Last edited:
Back
Top