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Paint Blisters/Fuel Tank Rivets

No it means that proseal is always oosing out from the flush side of the rivet even though I did not dab the rivet first. I dab the hole before inserting rivet. I dont think I dabbed proseal on the inside after setting but I can check.
Best,
 
Expansion and contraction?

My QB tanks have several rivets with the bubbles only on the bottom. Painted light grey.

Ever leave a metal gas can in the sun. The gases will expand and deform it if it is not vented properly. Could the expansion and contraction of fully fueled tanks cause or contribute through contraction and expansion of these rivet points and allow gasses to escape through a few rivets?

Who cares about water, give me the weight of a jumbo margarita!
 
I have looked in a couple more quick build tanks and there is no sealant on the shop heads of any of the rivets. Goes against what the directions tell you to do if you build them yourself.

I coated mine. In a couple years I will let you know if it helped :D
 
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<<Good shop practice would have the builder encapsulate the shop heads of the rivets>>

Well, in the search for a cause, unencapsulated shop heads are a reasonable theory. Can we get data to support the theory? Can anyone confirm a paint bubble problem even with well coated shop heads?
 
The smoking gun ????

In reading carefully back through this entire thread I am becoming suspicious that the common factor in all failures is that the rivet SHOP heads (inside of the tank) have not been fully encapsulated with proseal. I think Rick Galati's recent post is onto something here.

I would surmise that the QB tanks do not have encapsulated heads....and that the specific owner-built failures (such as Kahuna) do not have encapsulated heads either.

I would suggest that over time with movement (wing flex, vibration, thermal expansion) the rivets without head encapsulation are more likely to weep microscopic volumes of fuel or fumes which will cause the paint to delaminate over an extended period.

I would say that there are probably plenty of tanks without full encapsulation out there that are not necessarily weeping at the rivets... but some are.

It would be interesting to know if ANYONE who has experienced blistering has fully encapsulated the shop heads (in a quality controlled and workmanship-like manner!!!)
 
Interesting...

Brantel said:
I have looked in a couple more quick build tanks and there is no sealant on the shop heads of any of the rivets. Goes agains what the directions tell you to do if you build them yourself.

I coated mine. In a couple years I will let you know if it helped :D
My shop heads are coated (at least the ones I could see easily). Must depend on who was doing the proseal work at the QB factory that day.
 
Hard Knox said:
Ever leave a metal gas can in the sun. The gases will expand and deform it if it is not vented properly. Could the expansion and contraction of fully fueled tanks cause or contribute through contraction and expansion of these rivet points and allow gasses to escape through a few rivets?
Well, our tanks are vented, so the pressure inside should not increase much at all. If the pressure inside the tank is higher than atmospheric pressure, air will escape out the vent line until the pressure equalizes. If the vent is blocked, you would have a problem when you used fuel from that tank, so that condition would be detected.
 
At the risk of blowing myself up, could I use a boroscope in a 1/4 full tank ? It is a avery kind with a light on the tip ? I will not submerge the scope, only look where it is dry.
 
Solvent pops vs. blisters

We experienced some solvent pops at a few of the rivets, not necessarily at the tanks. There are a few possibilities that may have attributed to these small pin holes according to professional painters that we have talked to about this issue.
-water remaining under the head when primer, then top coat is applied.
-topcoat is too thick, resulting in solvent releasing thru the flashed off topcoat. This is like several little volcanos around the rivet head. Rivets create little pools that can hold too much paint if the coating application is too heavy.
-cleaning solvent left under the rivet, meaning we did not use enough clean water rinse after scrubbing with cleaner and scotch brite.
-scotch brite fiber stuck under the rivet head.
-using a turbine HVLP spayer, creating too much heat at the nozzle, forcing the paint to flash off too soon and trap solvents underneath, which then poke thru later. (little volcanos).
-too much humidity in the air when applying paint.
-too much reducer/hardner/thinner depending on temperature and humidity.
-not enough reducer/hardner/thinner depending on temperature and humidity.
-applying another coat too soon.
-combinations of the above.

I can't imagine there is a common thread when there are so many variables. A stab in the dark would be foreign substances trapped under the rivet heads and too much paint applied causing solvent pop around the rivet heads.

We have not experienced blisters and could only guess that some sort of contamination has occured under the paint/primer.

Pat Garboden
Ozark, MO
Todd Wiechman
Wichita, KS
RV9A 942WG (reserved) paint stage
RV9A 942PT (reserved) wiring stage
 
We're talking fuel tank blisters here.

gorbak said:
I can't imagine there is a common thread when there are so many variables. A stab in the dark would be foreign substances trapped under the rivet heads and too much paint applied causing solvent pop around the rivet heads.
Pat Garboden

Pat, of course you can get general coating problems, including trapped solvents, if the preparation and paint job on a plane are not done properly.

HOWEVER, what we are talking about here is specifically blistering on rivets AT THE FUEL TANK ONLY and where they do not appear anywhere else on the entire plane. This has proven to be a very common phenomenon.

The ONLY logical conclusion one can draw from this particular phenomenon is that the blistering is caused by fuel or fuel vapour weeping through rivet holes.

To date, no-one has reported a case of this occurring on fuel tanks when their shop heads (inside the tank) have been fully encapsulated.

I again request anyone who has experienced blistering on tanks with fully encapsulated shop-head rivets to step forward. If no-one comes forward I think we can conclude what the problem is.
 
Captain Avgas said:
Pat, of course you can get general coating problems, including trapped solvents, if the preparation and paint job on a plane are not done properly.

HOWEVER, what we are talking about here is specifically blistering on rivets AT THE FUEL TANK ONLY and where they do not appear anywhere else on the entire plane. This has proven to be a very common phenomenon.

The ONLY logical conclusion one can draw from this particular phenomenon is that the blistering is caused by fuel or fuel vapour weeping through rivet holes.

To date, no-one has reported a case of this occurring on fuel tanks when their shop heads (inside the tank) have been fully encapsulated.

I again request anyone who has experienced blistering on tanks with fully encapsulated shop-head rivets to step forward. If no-one comes forward I think we can conclude what the problem is.

The few shop heads I can see looking through the fuel cap hole with a flash light are not covered with proseal - QB tanks.
 
Evidence all pointing one way.

David-aviator said:
The few shop heads I can see looking through the fuel cap hole with a flash light are not covered with proseal - QB tanks.


David, everything posted on this thread to date supports the Rick Galati theory, including your experience. His theory is that over time rivets that do not have their shop heads fully encapsulated in proseal are more likely to weep minute quantities of fuel or fuel vapours and cause delamination of the adjacent paint. That seems totally logical to me.

Brian Chesteen reported that he has looked inside a couple of QB tanks and observed that the shop heads were NOT encapsulated with proseal. On the other hand Jase Vanover reports that his QB shop heads ARE encapsulated (at least the one's he can see).

In other words we have definitive proof that the QB tanks are not being contructed to a single quality control standard. Some have the shop heads encapsulated and some do not. Either that or the construction process was changed by Vans at some stage. I'd bet it's the former.

To date EVERY report we have had (builder-built or QB) of paint blistering adjacent to tank rivets has involved a tank constructed WITHOUT fully encapsulated shop heads. There have been NO reports to date of blistering occurring on tanks WITH fully encapsulated shop heads.

This is a very active thread with 60 posts to date and over 1268 views. I again ask any flying builders (QB or Slo-build) who have fully encapsulated shop heads AND have experienced blisters only on their tank rivets to report to us.

If no-one with full encapsulated heads reports a failure I think we can conclude what the problem is.
 
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The plot thickens.....and a conclusion.

I asked Vans if they have a manufacturing specification on the QB tanks requiring full proseal encapsulation of the rivet shop heads. No such spec exists. They only require that the QB tanks pass a pressure test.

So we now know why some QB tanks have full proseal encapsulation of the shop heads....and others do not. It's left up to the subcontractor who obviously changes his mind from time to time, depending on the success he's having with the pressure test.

To date, not one builder with either QB or Slo-build tanks that has rivet shop heads fully encapsulated in proseal has reported tank blisters. EVERY case of blisters reported to date DOES NOT have encapsulated shop heads.

So it is obvious what the problem is. With movement over time, some tank rivets weep microscopic quantities of fuel (or fuel vapour). Most don't, but some do. The fuel eventually causes delamination of the primer adjacent to the rivet.

Completely encapsulating the rivet shop head (inside the tank) eliminates the problem.
 
Captain Avgas said:
I asked Vans if they have a manufacturing specification on the QB tanks requiring full proseal encapsulation of the rivet shop heads. No such spec exists. They only require that the QB tanks pass a pressure test.

So we now know why some QB tanks have full proseal encapsulation of the shop heads....and others do not. It's left up to the subcontractor who obviously changes his mind from time to time, depending on the success he's having with the pressure test.

To date, not one builder with either QB or Slo-build tanks that has rivet shop heads fully encapsulated in proseal has reported tank blisters. EVERY case of blisters reported to date DOES NOT have encapsulated shop heads.

So it is obvious what the problem is. With movement over time, some tank rivets weep microscopic quantities of fuel (or fuel vapour). Most don't, but some do. The fuel eventually causes delamination of the primer adjacent to the rivet.

Completely encapsulating the rivet shop head (inside the tank) eliminates the problem.
Bob: I hope you are right, and it is that simple but I don't think so. I have built an RV6A and an RV7A both slow build so that makes 4 tanks. I built all four of them the same way and I completed covered the shop heads inside the tanks. ""They all passed the pressure test. The only difference was the way I painted them. The 6A was vinel wash, epoxy primer and Jet glow urethane. No problem. The 7A was Mar hyde self etching primer and jet glow. I took a short cut and paid for it. Blisters on the tank rivets. As I said I hope you are right and it is just vaper leaking out.
 
Captain Avgas said:
To date, not one builder with either QB or Slo-build tanks that has rivet shop heads fully encapsulated in proseal has reported tank blisters. EVERY case of blisters reported to date DOES NOT have encapsulated shop heads.

So much for that. :(
 
casper said:
Bob: I hope you are right, and it is that simple but I don't think so. I have built an RV6A and an RV7A both slow build so that makes 4 tanks. I built all four of them the same way and I completed covered the shop heads inside the tanks. ""They all passed the pressure test. The only difference was the way I painted them. The 6A was vinel wash, epoxy primer and Jet glow urethane. No problem. The 7A was Mar hyde self etching primer and jet glow. I took a short cut and paid for it. Blisters on the tank rivets. As I said I hope you are right and it is just vaper leaking out.

Doyle, a couple of questions.
1. Did you specifically encapsulate EVERY shop head with proseal AFTER rivetting.
2. Do you have any blisters ANYWHERE else on the plane apart from the rivets on the tanks.
 
I first noticed this same problem on only one of my tanks today. The plane was painted roughly 8 months ago using Stewart Systems Ekopoly system. I currently have 4 blisters. 3 are about 1/4" diameter, the 4th is 1" diameter. All four are on the same tank, bottom surface only. Before I popped one of the blisters to see what was inside, I decided to come home and check the forum for insights. Doesn't appear to be a good answer or explanation. What I'm obviously most concerned about is the fix.

I'll open up one of the blisters today and see what I can learn.

Jeff
 
Fuel migration

In my opinion and based on the information provided I think it is virtually certain that paint blisters occurring ONLY at fuel tank rivets are caused by microscopic amounts of fuel migrating adjacent to the rivet.

If fuel migrates it may eventually cause delamination of the external prime coat.

The reason why fuel can migrate up rivets on some tanks and not on others is open to speculation. It is relevant however that there has been only one report of blisters on a tank with fully proseal encapsulated shop heads. Every other instance had no encapsulation.

Builders might like to consider that even handling rivets with bare hands when building tanks might leave contamination on them that effects the adhesion of the proseal to the rivet. The correct technique would be to solvent wash the rivets and handle them with clean gloves.

Fully encapsulating the shop heads in proseal should also provide insurance.
 
Here's my theory on why this phenomena occurs. I have had blisters occur top and bottom of my tanks, over a period of few years maybe a dozen or so have popped up. I believe what happens is a slug of fuel gets into the vent line which effectively allows the tank to pressurize if there is a temperature change. The slight pressurization of the tank left that way for hours or days on end can cause the bubbles to form in the paint, as fuel and/or fuel vapor makes its way around tiny holes around the sealed rivets. Perhaps a small amount of liquid fuel introduced to the outer surfaces of the tanks helps the paint delaminate which eventually vaporizes and disappears in liquid form. The only way these bubbles can form is with pressure. On my F1 project I intend to plumb the vents so they just go straight down from the inboard fitting, no loop inside the fuselage or in the wing root. That way the vent can drain, and certainly should expect to see more fuel coming out of the vent.
 
Our RV is starting to develope these bubbles/blisters..

Is it worth repairing or will it just do that again?
 
blister picture

I've noticed through all of these threads that no one has posted a picture. Here is mine. As a data point....paint is Dupont, base/clear, primer is DB40 epoxy, skin was scuffed with scotch brite and washed down with laquer thinner. Although the pressure in the tank theory may be correct for some tanks, mine is definitely not one of them. All of these rivets are on the non-fuel side and one tank only. Whatever the cause, I just don't think it's a pressure thing.
dscf0765mi5.jpg
 
I've noticed through all of these threads that no one has posted a picture. Whatever the cause, I just don't think it's a pressure thing.
My theory is well known....so naturally I'd be interested to know if the shop heads of the rivets were properly encapsulated. So far, I've seen no real evidence....none so far....that would cause me to abandon my theory about the root cause of this problem. Since in your case the blistering seems to occur along the back baffle, removal of the tank from the wing would very quickly confirm if the rivets were encapsulated or not. If they are encapsulated...and you provide us with detail photos of acceptable encapsulation......I would then resume my place among all others who have no real idea as to what is causing the problem. If however, in your case the shop heads of the rivets are not properly encapsulated, I believe you (unlike many others) can anticipate a relatively easy fix.
 
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To put this whole blistering story to bed. IT IS CAUSED BY FUEL !!!
Blisters only occur on the tanks. So only the tank sealant or its application is to blame. Start by using a different brand of sealant .
This is my opinion and I would put money on it. FWIW I also had blisters as well as sealant going soft on the outside of the root rib.QB tanks. I tried replicating this using a different supplier of tank sealant with no success.
If i were to build again I would go slow build on the tanks with a better tank sealant.
 

First evidence of blisters with my QB tanks was along the bottom aft flange as per the image. That was some 3 years ago. The blisters now are evident top and bottom at nearly every rib. I've seen a couple new ones this summer. They just keep coming. An inspection with flashlight through the fuel cap reveals some shop heads not covered with pro seal.

Is there a way to forward this entire thread to Van's? Seems like they ought to be interested in getting to the bottom of this problem and coming up with a fix. If it is affecting just 10% of the fleet, that is some 500 hundred paint jobs screwed up. Considering that many affected tanks are QB, the cause is related to factory methods to build the tanks.
 
Not meant as any disrespect to Vans, but I have always felt they market their product as "affordable" and things like the blistering does not bother them as it is not a safety issue.
Forwarding this thread to them will be futile. IMHO.
 
Other factors to consider?

I signed up just to weight in on this blistering issue - I was thinking about some other factors to consider:

Fuel types - potental failure mode 1.- if the proseal (or its likeness) is permeable to short chain HC fractions of the fuel then the higher temp of the sealant could be penetrated by this vapor and since primers are porus, then the minute amount of vapors are stopped at the top coat layer. Either flying or sun heating and expansion results in the separation of the top coat and thus a blister. pressure collects factor 2. #1 + debonding of topcoat to lower adhesion due to vapor type.

Just a thought, but in looking up the mil spec (mil-s-8002XXX) it always looked at aviation fuels using a "jet reference".

Idea #2: Temperature of fuel - what is relevance of fuel system type - recirculation types (injected) are more prone to add temperature to returning fuel and possible increase the vapor pressure of some fractions. ( a low probability, little out on a limb here)
 
Just a few more points. I too would be curious what the back side of the baffle around those rivets looks like. I haven't had the tank off yet to look but it will be easy to check, once I do. Also, that tank is the only one that has only had Av gas in it. I keep one tank solely for Av and the other has auto or Av gas. I really think it is a fuel issue also, but am hesitant to just strip the tank and paint it again and have the same problem.
 
A few weeks ago I went to Downtown Island Airport in Knoxville, Tn to help a friend weigh an RV7A soon to be test flown, it had blisters as well on the baffle rivets. This was a QB and I looked inside and the rivets did have proseal on the tails.
 
Has anyone had any luck sealing the rivets from the outside? I have one with blue streaks and I'm looking for the best way to fix it.

Has the green locktite trick ever worked?

Any magic cures?
 
I had a similar problem when my plane was at the painters being prepped for paint. I applied a shmear of JB Weld (the only stuff handy at the time) over the rivet head. Problem solved.
I regularly check my tank fasteners for leakage. Thankfully, there has been none. Several have blisters on them, though. As long as they are not leaking I will leave them alone.
 
Pro Seal Retired?

While considering the cost of building new fuel tanks, I noticed Van's no longer sells pro seal.

Now that's interesting, maybe the stuff isn't perfect after all.
 
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a different idea on the rivet blisters?

Hi all, I'm building an -8QB and I've been reading as much as I can find on this thread of the paint blisters on the rivet heads. I did have an observation to add that might have not been brought up.

There was at one point a tentative conclusion that the problem related to rivet shop tails that were not completely encapsulated with Proseal. I just wanted to point out that many of the blisters seem to be forming on the rivets on the rear baffle, where the shop tails are not inside the tank - so it wouldn't matter if they were encapsulated or not - thats not where the vapor is coming from in those cases.

My impression from absorbing all the comments is that the pro-sealed rivets are not truly vapor tight, and even the slightest weakness of paint adhesion is probably enough for the vapor to form a blister.
 
Loctite 290

I did find a posting in the Falco forums about using a wicking sealant like Loctite 290 to seal a leak in a welded aluminum tank. It seemed to be successful. In that case, they used a slight vacuum to help pull the sealant into the leak. In my case with 'virgin' QB tanks, I'm thinking I will just put a little Locktite 290 on each rivet head as a belt-and-suspenders approach to maybe sealing it up enough to prevent the blisters.

(appologies if this duplicates, my last post was sent before I finished by mistake)
 
The picture still shows Flamemaster, producer of the original Proseal right? Aren't they the same even though the catalog lists it by mil-spec instead of Proseal? the B- designation If I recall, pertains to the working time, i.e. B-2, two hours?
 
Could it be pressure related?

My -7A has the paint blisters, but only on the rivets on the top of the wing. It took about 6 months after paint before this happened. I think this is what most people experience.

I have noticed that if you (over)fill up your tank when it is cool and let the plane sit in the sun, it builds up a lot of pressure and actually blows fuel out the vents. I took my gas cap off one time to see how much pressure was in there and POW, nearly blew the cap off in my hand. Since there is fuel in the bottom of the tank, all the air and pressure are pushing up on the skin and rib attachment rivets at the top of the tank as the fuel and tank warms in the sun. This pressure can take a while to relieve itself as evidenced by the fuel spurting out the vent lines. This constant expand/contract rhythm may be causing this phenomenon on the upper tank rivets. This would explain why the baffle rivets blister as well. Any thoughts on this?
 
ProSeal is not FlameMaster

The picture still shows Flamemaster, producer of the original Proseal right? Aren't they the same even though the catalog lists it by mil-spec instead of Proseal? the B- designation If I recall, pertains to the working time, i.e. B-2, two hours?

No... ProSeal is a PRC/DeSoto product and is now owned by PPG...

FlameMaster is a completely different company, in existence since 1942, and not owned anyone else as far as I can tell....:)

As I mentioned before - they both meet the same specification...

gil A
 
Different Perspective

At work we recently completed testing of our aircraft's coating systems against some nasty compounds - the kind unfriendlies might distribute to keep us on the ground. The test coupons were fully cured, robotically-sprayed pieces of structure representing optimum application and process control. The spray equipment represents the most state of the art robotic technology in terms of thickness control and mixing capability. The few blisters that occured did so in benign areas - meaning no protuberances or breaks in the surface. The entrapped gas/air and the internal surfaces of the blisters were spectrally evaluated and determined to not contain the slightest trace of agents. The analysis indicates that despite our very best efforts to mix the material the agents reacted with unmixed or uncured elements. There is also some thought that trace elements of the hydrogen peroxide decontaminate crosslinked with embedded sulfur compounds to caused dioxide to form, thus a blister (bubble). Could be a similar chemical/mechanical interaction going on with pro-seal and fuel or fuel and primer?
 
<<The analysis indicates that despite our very best efforts to mix the material the agents reacted with unmixed or uncured elements.>>

Ya'll remember that one when you get tempted to think precise ratio control isn't necessary...mixing epoxy, proseal, polyester, whatever.

<<There is also some thought that trace elements of the hydrogen peroxide decontaminate crosslinked with embedded sulfur compounds to caused dioxide to form, thus a blister (bubble). Could be a similar chemical/mechanical interaction going on with pro-seal and fuel or fuel and primer?>>

Hmmm. 7000+ members....do we have a chemist in the house?
 
Ratio vs Mixing

Ya'll remember that one when you get tempted to think precise ratio control isn't necessary...mixing epoxy, proseal, polyester, whatever.

Not quite the right observation from our data, which is "do a really good job mixing 2-part systems". Within reasonable limits, precise ratio control effects pot life, not mix (final product) quality. However, if too little catalyst is applied there may be insufficient crosslink and the material may never achieve final quality. Too much catalyst usually just reduces application time.
 
Ya'll remember that one when you get tempted to think precise ratio control isn't necessary...mixing epoxy, proseal, polyester, whatever.

Not quite the right observation from our data, which is "do a really good job mixing 2-part systems". Within reasonable limits, precise ratio control effects pot life, not mix (final product) quality. However, if too little catalyst is applied there may be insufficient crosslink and the material may never achieve final quality. Too much catalyst usually just reduces application time.

I have not counted blisters over pro-sealed rivets but after 4 years they just keep coming and at this point probably 70-80% have done it.

These tanks were Quick Built by foreign workers and I have felt all along the problem is proseal not properly cured for whatever reason. For sure the blisters are not caused by improper pre paint prep resulting in filiform corrosion, as was suggested by the factory. The entire airplane was prepped and painted by one person and the blisters have occurred only over rivets treated with proseal. Fuel as a factor is also ruled out because there is no fuel at the aft flange, the rivets are outside the tank and that's where the blisters showed up first.

One of these days when I become totally tired of looking at the problem, I will build two new tanks.
 
I amy have missed it, but has anyone identified the exact sealant brand and PN applied at the QB facility? Can't chase Bill's idea if we don't know the chemistry. Seems like we need a MSDS at a minimum.

Bill, very good point about mixing. I'm guessing the QB folks use a cartridge system. How well do cartridge systems really mix?
 
Fuel as a factor is also ruled out because there is no fuel at the aft flange, the rivets are outside the tank and that's where the blisters showed up first......
Dave,

I would be very reluctant to conclude that just because "there is no fuel at the aft flange" that fuel is not a factor. Indeed, I strongly suspect more than ever that improper application of proseal is the root cause of the problem. Just because one or two builders have asserted (without I might add, any photographic documentation) that their tank rivets were properly encapsulated and still experienced paint blistering is hardly conclusive of anything. Quality control is the major wild card here. Without a clearly defined and strict quality control standard, "adequate" or "acceptable" or "good enough" are merely relative terms open to virtually any degree of personal interpretation. What I do know is this. Your photographs of your own quickbuild fuel tank innards clearly indicated a lack of shop head encapsulation. That significant little detail alone clearly violates Van's own written instructions when the tanks are builder assembled. If the foreign worker who built those tanks was lax about doing that because it is tedious and time consuming work, why would you suppose he was particularly concerned about carefully applying a proper bead of sealer around the perimeter of aft flange prior to inserting the back baffle? Remember, all that tank has to do is satisfy a pressure test before being released from the shop.

This I also know. When you shoot or squeeze rivets into very wet sealer, in reality only a thin film of sealer remains between the parts because the majority of the sealer is squeezed from between the parts in the riveting process. If the builder fay sealed in a manner that allowed ANY voids to exist in that remaining thin film of sealer...it is all the more reason to suspect that fuel or fuel fumes could eventually find its way into a void or voids hidden within that fay sealed surface.

It is perfectly reasonable to suspect that ANY voids in a proseal boundary whether it be under the manufactured head or the shop head or even between parts...such as at the aft flange that you mentioned could, could be the cause of the paint blistering and as of yet no one has offered up any real, meaningful evidence to the contrary that would compel me to change or at least modify my opinion.
 
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I amy have missed it, but has anyone identified the exact sealant brand and PN applied at the QB facility? Can't chase Bill's idea if we don't know the chemistry. Seems like we need a MSDS at a minimum.

Bill, very good point about mixing. I'm guessing the QB folks use a cartridge system. How well do cartridge systems really mix?

I know nothing of the overseas operation so I can't say for sure. If they do use Semkits (the tube) I would assume (hope) they also have semco mixers which do a very good job mixing. If they manually mix them it's anyone's guess. I'd rather have a tooth pulled than manually mix more than one tube - it's hard work and fraught with variability. The nice thing about using bulk (can) pro-seal and flamemaster is the contrasting color of the two parts. It's pretty easy to see unmixed parts if you use a transparent mixing cup. I was confident of a good mix when I sealed my tanks but I was worried about the quality of the job because my hands were so tired from mixing!:rolleyes:

I've been thinking about the variables in this issue. If my work experiment applies (an oxide meeting sulfur to chemically react to form a pressure bubble), there's sulfur in Polysulfide and minute particles could be reacting with fuel or fuel additives or could be reacting with something in the paint system. I don't have a feel for how long paint remains "active" but fuel and fuel vapor is certainly ever-present. A gaseous path from within the tank can exist where fluids can't pass - thus the dry blisters, but primer/paint reacting to the ring of pro-seal around the rivet could also be the cause. I suspect the non-tank applications of pro-seal point away from this, though. Fuel-wet blisters leave little doubt that a leak path was inadvertantly built in so the dry blisters are more interesting. Fuel is blended differently for each state and for each season, so we'd have to look at the additives for a lot of different applications and determine if any of them could chemically bond/react with pro-seal. We'd also need to look at the primer/paint systems.

I'll explore this with the chemists around here if everyone who has blisters would fill out the following datapoints:

Fuel wet or dry blisters (fuel tank):
Non-tank/pro-seal blisters:
How Many:
Top or Bottom:
Hours in Service When Appeared:
QB or Slow built:
Wet-installed rivets or dry:
Shop head sealed (well):
Fuel Brandname:
Avgas or Mogas or Blend:
State of (fueling) Residence:
Hangared or Stored Outside:
Primer system:
Paint System:
Fuel Injected or Carburator:
Pictures of Blister:
Pictures of Rivet Shophead:

Did I forget anything?
 
paint blisters

i took my plane back to paint shop for blister repair. he used some kind of acrylic on each rivet after removing the blister. those blisters have not reccured but some who were not treated are blistering. all on top of the fuel tank area. only on the top surface. i will ask the painter to remove all the paint on top of the fuel tanks , seal all the rivets like he did before and repaint. robert n661g corpus christi, hot all the time.this is a qb kit
 
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It is a universal truism that success in most endeavors lay “in the details.” Especially so when it comes to airplane construction, close attention to detail often separates the craftsman from the hack, the outstanding from the mediocre, and especially so when we are discussing fuel tank construction... trouble free from troublesome.

Although no definitive cause has been officially determined as the source of the paint blistering problem many builders have reported, my long held suspicions are known, remain unchanged and summed up in post 97 of this thread. Despite the assertion of some builders who claim to have properly assembled their own fuel tanks yet still suffer paint blistering problems and seek to assign blame to some other cause (most commonly if not conveniently) “defective proseal,” the fact is this: No one to date has yet offered up any real meaningful argument or photographic evidence to support that assertion.

I submit the following photographs and I think the images lends credence to my long held view that sloppy craftsmanship and/or improper application of proseal could very well be the source of the random and vexing paint blistering problem. During a routine technical counselor visit, I had the opportunity to closely inspect a pair of older RV-6A quickbuild fuel tanks. It is important to note that these fuel tanks have NOT been installed or even filled with fuel yet. It is also important to note that the construction manual clearly directs the standard kit builder to "dab" sealer on the fuel tank rivet shop heads....in other words, encapsulation. The photographs that follow are only a portion of what I saw and documented. Apparently, subcontracted fuel tank assemblies have only to pass a pressure test to be cleared for eventual sale. Fair enough. But let us understand that paint blistering is a much more subtle phenomenon than obvious leaks discovered during a routine pressure test. Indeed according to some posters, paint blistering may not show up for some time and then become progressively worse months, even years after the plane has been painted. I’ll leave it up to the viewer to draw his or her own conclusions about what I observed taking these photographs.

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Now, I will concede here and now that strictly speaking, rivet shop head encapsulation may not be required on those rivets exposed and in view outside the tank. I prefer to encapsulate those rivets anyway for no other reason than it is very easy to do and the best way I know how to communicate this dynamic........image a soda straw held vertically, filled with fluid and open at the bottom. The only thing keeping the liquid within the straw is your thumb sealing off the top opening. Granted, this an arguable point but I freely admit when it comes to fuel and potential leaks, I tend to errr on the side of conservativism.
 
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Rick - just to clarify - ALL those pictures are from a QB tank? That's a little scary....
 
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