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Weird paint bubbles. Looking for a cause/solution

Darren S

Well Known Member
I first noticed these weird dome shaped paint bubbles during my pre-OSH clean up.

History: Plane was built in 2006, not by me, has 725 hours on it, 500 by me.

I've never noticed these before. In my haste to pack up for OSH I cut into a couple of the bubbles, then using thumb pressure crazy glued the paint back down. Upon returning from the trip I now notice several more. Something is going on.

This paint phenomenon is only on the underside of the right wing. The bubbles appear along the aft rivet line on the tank.

I suspected some sort of tank leak but there was no blue AVGAS trail when I cut into the bubble. The areas I fixed with the crazy glue seem to be ok ie. no re-occurance of bubbling.

Anybody seen this before ? Please tell me I don't have to take the tank off ?!! How to fix ?

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Thanks,

Darren
 
The bubbles appear to be around or on rivets that are part of the fuel tank.

If that's the case, leaky rivets on fuel tanks have been the scourge of paint jobs for years. A search for "weeping rivets" or something like that will probably get you an evening's reading.

None of the solutions are easy. Doable, yes. Easy, fast, or cheap, no.
 
Fuel tank rivet paint bubbles

You'll find lots of information if you do a search on fuel tank rivet paint bubbles or some combination. Lots of data, no definitive solutions. Most likely insufficient proseal on inside of tanks allowing fuel to weep under the paint and blister the paint.
 
I dug through the aircraft journey log. Looks like back in 2009 a paint blister was repaired on the underside of the same wing.

Also, reading the archives I've learnt that, since the bubbles are full of air and not gas, I may be having some tank "pressure" issue, not necessarily a fuel leak.

No solutions yet though.

Darren
 
I first noticed these weird dome shaped paint bubbles during my pre-OSH clean up.

Darren

Darren, this is the definitive VansAirforce thread on the matter if you have not already found it.

http://www.vansairforce.com/community/showthread.php?t=10187&highlight=paint+blisters

I don't believe there is any mystery now to this phenomenon. It's caused by lack of quality control in the initial fabrication of the tanks. Rick Galati has outlined the issue and his posts 100, 105, 113, 135, 207 and 289 are all worth reading.

It is possible that some sort of pressure differential might exacerbate the problem....but the root cause is poor workmanship in the initial application of the proseal.
 
Hey Bob,

Thanks for the link. I spent all last night and this morning reading it. Lots of talk on higher level chemistry and lab testing etc....

Seems like the cause is obvious but no one chimed in on a possible external fix. At least none I could find. I really don't want to pull the tank off at this time so I tried my own thing this morning.

I'm thankful that my bubbling issue is only on the underside of the right wing, and about 8 spots. SO FAR:)

Here's what I did. I mounted a pencil in a cordless drill. Lead end in the chuck. On the eraser end I double sided sticky taped a small piece of 220 grit sand paper. I spent an hour and sanded through the bubbles and cleaned a couple of millimeters around the rivet head. Down to bare metal and feathered the ends. I took acetone and gave all the dime sized defects a good cleaning. The defect areas were slightly countersunk. Then I skimmed some JB Weld in the defect and with a straight edge built up the countersunk area. Much like we've all done with Bondo. It's only a few paint layers thick.

I'll lightly sand and apply some brushable touch up paint tomorrow.

Will other bubbles appear? Probably:) Will bubbles reappear in these areas? Probably:). I'm just trying something. Pulling the tank is a last resort for me. A Winter project if it gets to that. I trust the JB Weld more than the loctite suggested in the other thread.

Darren
 
The defect areas were slightly countersunk.

Bingo.

Will other bubbles appear? Probably:)

When they do, please measure the actual outer diameter of the cut countersink before you fill them with JB Weld.

0.1790" is perfect
0.1814" is .001" too deep
0.1838 = .002
0.1862 = .003
0.1885 = .004
0.1909 = .005
0.1933 = .006
0.1957 = .007

It's easiest done using a 10X magnifier and a plate with pre-sized holes. Just find the hole matching the countersink diameter.

1iij3q.jpg
 
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Hey Bob,

Thanks for the link. I spent all last night and this morning reading it. Lots of talk on higher level chemistry and lab testing etc....

Seems like the cause is obvious but no one chimed in on a possible external fix. At least none I could find. I really don't want to pull the tank off at this time so I tried my own thing this morning.

I'm thankful that my bubbling issue is only on the underside of the right wing, and about 8 spots. SO FAR:)

Here's what I did. I mounted a pencil in a cordless drill. Lead end in the chuck. On the eraser end I double sided sticky taped a small piece of 220 grit sand paper. I spent an hour and sanded through the bubbles and cleaned a couple of millimeters around the rivet head. Down to bare metal and feathered the ends. I took acetone and gave all the dime sized defects a good cleaning. The defect areas were slightly countersunk. Then I skimmed some JB Weld in the defect and with a straight edge built up the countersunk area. Much like we've all done with Bondo. It's only a few paint layers thick.

I'll lightly sand and apply some brushable touch up paint tomorrow.

Will other bubbles appear? Probably:) Will bubbles reappear in these areas? Probably:). I'm just trying something. Pulling the tank is a last resort for me. A Winter project if it gets to that. I trust the JB Weld more than the loctite suggested in the other thread.

Darren

Darren,

It is not a safety of flight issue so don't ground yourself over it.

I flew with much worse blisters for several years. After the initial shock of seeing them the first time, you gradually get used to it. I did not let it detracted from enjoying the great flying qualities of the airplane - it is a cosmetic issue.

I do not have an easy fix for it but that's not to say there isn't one.
 
Hey Mike,

I ran the cordless drill slowly and removed the clear coat, paint and primer. I extended things until the rivet head was completely exposed. Deepest area of the preparation is probably the thickness of your fingernail, at most.

So I did create the countersink.

Who knows if this crazy idea will work. I had to try something. I know it's not flight safety related. Thankfully:) and I'm thankful it's on the side of the wing only the gophers see:)

Darren
 
More new bubbles.

Much to my disappointment, paint bubbles now have appeared on the top of the left wing :(

6 years, 700 hours and nothing, now in the span of 3 weeks, a dozen.

I am going to leave them for now and then during the winter down time I'm going to pull both tanks.

I found a local guy who has repaired these types of things before. His way is to cut a hole in the rear baffle of each tank bay and apply Proseal. Then close up the opening.....obviously :)

I'll have to get the tanks repainted afterwards as my ugly JB weld fix is just that.... ugly!

So it won't be easy or cheap but I can't let my baby fly around the skies with pimples on her face :)

Darren
 
6 years, 700 hours and nothing, now in the span of 3 weeks, a dozen.

Think hard.....what have you done different lately? Pulled G's, hard landing, high temperatures, new fuel shipment at your home airport, parked empty, parked full, used auto gas, got too close to another RV with blisters.....anything?
 
After 90 hours on the Hobbs, I found my first blue rivet, top of rear baffle. My tanks are unpainted so I plan to pull the tank, remove the rivet, clean up the countersink, liberally apply proseal and squeeze.

Could it be the blistering summer heat??
 
My 2.5 cents...

Darren,

It almost defies explanation the rate at which your tank is producing blisters. I would suggest that you consider a new replacement tank rather than having the existing tank repaired. Patching multiple leaks through access panels is very labor intensive and the long term results are far from certain. Until the tank is opened, it would be difficult for the shop to give you an accurate estimate of repair costs.

I would bypass the uncertainties of the tank repair and opt to purchase a new tank from Van’s with the intention of building the tank yourself or hiring someone to build it. Five years ago, as a buyer, I had looked at an -8A for purchase. The owner failed to tell me that both tanks were blistered on top and bottom (note to future buyers, ask that question before leaving home). Upon inspection of the aircraft, I counted over 60 blisters. I contacted Van’s about the costs of new tanks. Buying two tanks, having a shop in Northern California (forgot the name) build them for about $900, and then have the tanks painted at home, the estimate was about $3200 USD.

Before committing to the tank repair, give Van’s a call for an updated price of a completed tank. This may be the safest and most cost effective way to go.

Regards,
 
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Before committing to the tank repair, give Van?s a call for an updated price of a completed tank. This may be the safest and most cost effective way to go.

May be.....but even new replacement tanks from well known pros have blistered.
 
Maybe it is not a fuel issue. I have not built an rv yet, but I did build a velocity. There was a concern of air being trapped in pin holes under paint. When you flew up high the air pressure difference eventually wore the paint and blisters appeared.

So now to the rv. if the dimples were done with tank dies and they are deeper, maybe there is air trapped under the paint or primer, or is there thicker paint there causing the bubble to start. There are theories about fuel leak or bad proseal application, even paint prep.

Has anyone looked at regular dies verses tank dies, or as one post mentioned are the dimples deaper than need be?

Bob K
 
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May be.....but even new replacement tanks from well known pros have blistered.

Yes, it is a bit of a **** shoot...but all things being equal, I would take my chances with a new tank.
 
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Hi Darren, please excuse my naivety but out of interest, do you know if the wings were QB when originally purchased in 2006? If not, do you have any idea if this is likely to happen to QB wings?
 
Yes, it is a bit of a **** shoot...but all things being equal, I would take my chances with a new tank.

I'd take the re-seal, and here's why. The standard assembly method slides the rear bulkhead into place to close the tank. That means it is not possible to install a proper sealant fillet along the bulkhead-to-skin seam. The best we can do is sort of a bow wave of sealant pushed up along the seam as the bulkhead slides into place.

A nice smooth concave sealant fillet is the ultimate seal. The very thin sealant film between components (as little as 0.001" thick near the fasteners) is subject to rupture by relative movement due to structural and thermal loads. The thick sealant fillet easily accommodates any relative movement. Of the three seal types (fastener, fay, and fillet), fillet sealing is the most reliable in service.

Going in via access openings allows fillet formation along all seams.

27zcbrq.jpg


35annza.jpg
 
This is not to say Dan's suggestion is without merit but to submit another perspective on resealing offending fuel tanks.

I opened my tanks before deciding to build new tanks. After some 5 years of using 100LL and mogas I found a thin film of unknown residual matter all over the inside of the tanks. It was not a build up but just a film that would be removed with a swipe across it with a rag.

It was decided it would be very difficult to sufficiently remove this matter to provide a sure seal between the old sealant (a light brown version of pro-seal from 2002 that was applied with a brush - the inside finish was very neat and smooth) and the new sealant, so I built new tanks. Truth is, I already had the tank kits on hand and it was not a difficult decision although I could have sold them.

That was a year ago. So far, my friend Jerry Cochran in Oregon who owns the -7A today has not reported a reappearance of blisters - and I keep my fingers crossed on that subject.

A lot of sealant was used building those tanks (and the tanks I just completed with the -8 build). Van's says "a single sealant kit should be enough for 2 tanks but some builders use more". I used more, one kit plus half of another plus 2 of the tube kits. I don't know if that is a guarantee of no blisters but the fact is, many tanks do not develop blisters and it may, as Rick Galati says, have something to do with the application the sealant (and maybe the quantity). The one caveat on using lots of sealant is a tank can end up slightly larger than when it was clecoed together and matched to wing leading edge, but fortunately Rick Galati has a cure for that outcome also. :) It was an easy fix shimming up the leading edge to match the tank. Purely cosmetic stuff.

Note: the old tanks had dozens of blisters, mostly along the bottom aft baffle rivet line but there were random blisters in other areas along ribs lines on the top and bottom of the tanks. The blisters did not appear all at once but continued to show up until the tanks were removed and replaced.
 
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I have blisters on both my tanks - only the tanks - top and bottom. Van said it's a builder issue while sealing the tanks, but they went silent when I reminded them that they were QB wings. In short, they don't want to know.
Personally, I think it's not a fuel issue at all - there isn't even a fuel smell when you pop a big blister. I'm convinced that it's actually a ProSeal issue. Think about it, it only happens on rivets that have ProSeal on them. Nowhere else.
John
 
David has a good point....used tanks would need cleaning. The tanks in the photo were brand new.

John, remember, proseal is used in airframe locations other than tanks, but there are no reported blisters in those locations.
 
Double-Walled Tank with Vented Interstitial Space

I'm just reading here, and trying to pay close attention since I'm now working on my wings. I hate the idea of doing my very best on the tanks and using even more proseal than is required and still ending up with paint blisters, so I'm trying to think outside the box.

Forgive me, but just a dumb question. Has anyone ever designed/built a double-walled tank, with say an 1/8" insterstitial space that was vented to the outside? It would be more work, more expensive, add more weight, and would reduce fuel quantity slightly, but if fuel did drip through the prosealed rivets or seams of the inner skin, such a small amount would evaporate via the vent before leaking through the outer skin. Plus, the outer skin wouldn't be subject to the hydraulic pressure of the fuel 24/7 during fllight or temperature variations on the ramp.

This would be a lousy solution, but since this seems to be such a frustrating problem, I can see where it could be a solution. Maybe some variation of a vented double-walled tank that more experienced builders could come up with.
 

That was a year ago. So far, my friend Jerry Cochran in Oregon who owns the -7A today has not reported a reappearance of blisters - and I keep my fingers crossed on that subject.

A lot of sealant was used building those tanks (and the tanks I just completed with the -8 build). Van's says "a single sealant kit should be enough for 2 tanks but some builders use more". I used more, one kit plus half of another plus 2 of the tube kits. I don't know if that is a guarantee of no blisters but the fact is, many tanks do not develop blisters and it may, as Rick Galati says, have something to do with the application the sealant (and maybe the quantity). The one caveat on using lots of sealant is a tank can end up slightly larger than when it was clecoed together and matched to wing leading edge, but fortunately Rick Galati has a cure for that outcome also. It was an easy fix shimming up the leading edge to match the tank. Purely cosmetic stuff.


David and I talked by phone today and agreed I would inspect the tanks he constructed last year for the -7a I purchased from him last fall. Today I checked the tanks and found no rivets with an issue. Because of medical issues and updates I'm doing to the plane, it has been a hangar queen for the past 6 months or so, but no issues with the tanks like others have seen

I note from this site that even QB tanks have had this issue and that Van's seems not to be involved in nailing down the cause. Interesting....

.
 
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Plastic fuel tank

I have a plastic 350 gallon water tank I use on the ranch to water some transplanted trees. It rattles around over terrain my Ranger ATV barely makes. It never leaks. I have had plastic portable gas cans for years - no problem. I know that the plastic water tank is much stronger than the tanks I am building for my -9. I was at the supplier yesterday and noticed all the different sizes and shapes of tanks.

With as many RV's as are built, I would think it would be worth it for a company to form a plastic tank that could slide in modified ribs. I don't know if the tanks on all the models are close enough so one size tube would fit everything, but I bet no more than a couple sizes would be needed. Maybe if the tube had to be smaller for fit, it could be longer and go through more ribs. Replacing the tanks might require wing removal or some other way, but to eliminate all chances of leaks, it may be worth it. With what is charged by tank builders and I can get a 350 gallon tank for $250, there is room for profit. I would pay a premium to eliminate the chance of leaks or blisters. Fixing a paint job is not easy or cheap.

In the picture, if the rib was cut on the blue line - or even closer to the edge, I think it could work.
904rib.jpg
[/IMG]
 
I'm no engineer, but I think a cutout that size on the tank ribs would very significantly reduce wing strength.
 
maybe not

I'm no engineer, but I think a cutout that size on the tank ribs would very significantly reduce wing strength.
I know I can stand on my tank and it doesn't bend at all. Think about the plastic kayaks - they are very strong. I think the tank may be able to be made that simply bolts onto the spar. The front - tank area of the wing is not the "support" for the wing - the spar is. The ribs hold the skin apart and allow for shear transfer to be rigid. Im not an engineer either, so I may be way off, but if the tanks were made to match the rest of the wing - no aluminum skin except maybe to fasten it to the wing, it could work. If you needed additional strength, interior baffles could be glued or formed in the interior of the tank. It might look corny - like a bumper on a car, but it wouldn't leak. I think the shape of the airfoil in the front of the wing is the critical item and doesn't provide much strength to the wing.

Imaging just being able to bolt on a new tank, plastic so it easy to clean, and almost damage proof. My water tank has been in the sun for 5 years and looks like new - with no finish on it at all.
 
Are all Brands of "pro-seal" equal?

This may have already been discussed but I haven't seen it mentioned here (in this post). Just to throw coals on the fire, I bet not everyone is using the same brand / grade of proseal. I'm about to be building my tanks in the near future... One look at ACS's website & a simple search for proseal yields several different brands at several different price points. HMMM! that's gotta tell you something about grades & quality. I know of a builder who got leaks years after this build was complete, upon inspection of his tanks, it seemed to him that the proseal never set up completely. Was this a case of bad proseal across the board for all proseal or just a bad batch made by one company. Call me crazy but could this issue be as simple a matter of you get whay you pay for. Kinda like habor freight tools vs. Cleaveland tools. Now if there was only one supplier of "proseal", you could definately figure out the failure point, the goo or the builder, correct? Just more food for thought.

Personally, I had thought a while back about doing what Dan H. did & put additional access plates in the tank to ensure a nice filet of sealant along the rear baffle (where most blisters are appearing first). Leaks in an access panels are way less painful to repair than a blistered $ 10K paint job.
 
It also only happens on rivets that are exposed to fuel. Nowhere else.

Aahh, very true. But, I used ChemSeal from ACS on the trailing edges, not ProSeal. Could it be a brand issue? Or perhaps it's a "curing" issue because of the thickness of the ProSeal....

As an additional data point, I have noticed that I'm getting fewer and fewer blisters over time. I always lance the back side of the blister with an Exacto knife and blisters "usually" shrink and rebond to the rivet. Only one has lost the paint in the airstream.
John
 
John, is someone keeping a database of what product is yielding the most blisters? Is that database available?
 
My Cessna 150 is 40 years old and has never had a paint blister from leaking fuel. I've had a small fuel leak in one tank at the level sensor, but it never blistered. Why? -- it's not a wet wing -- it has internal stand alone tanks, and there is no significant amount of fuel standing at the outer skin.

I'm sure there is some reason that we are building planes with wet wings, but why can't they be buillt with separate internal tanks or a bladder? What am I missing? Loss of aerobatic capability? I'd rather have a leak proof aircraft, or at least one that doesn't ruin a $10k paint job.
 
I'm sure there is some reason that we are building planes with wet wings, but why can't they be buillt with separate internal tanks or a bladder? What am I missing? Loss of aerobatic capability? I'd rather have a leak proof aircraft, or at least one that doesn't ruin a $10k paint job.

Sure there is a reason RV's have a (semi) wet wing tank... lighter and much less expensive.
Just like there is a reason other airplanes do have bladders or separate internal tanks (Cessna), and some have true wet wings (Mooney), and some have removable built up tanks like RV's (Piper Cherokee). All likely a result of different engineering decisions (you would have to ask them the reasons).
BTW, all of these other tank designs have also had their fair share of fuel tank problems. You can not assume RV fuel tank problems would be solved if they just had a different fuel tank design.
 
I know I can stand on my tank and it doesn't bend at all. Think about the plastic kayaks - they are very strong. I think the tank may be able to be made that simply bolts onto the spar. The front - tank area of the wing is not the "support" for the wing - the spar is. The ribs hold the skin apart and allow for shear transfer to be rigid. Im not an engineer either, so I may be way off, but if the tanks were made to match the rest of the wing - no aluminum skin except maybe to fasten it to the wing, it could work. If you needed additional strength, interior baffles could be glued or formed in the interior of the tank. It might look corny - like a bumper on a car, but it wouldn't leak. I think the shape of the airfoil in the front of the wing is the critical item and doesn't provide much strength to the wing.

Imaging just being able to bolt on a new tank, plastic so it easy to clean, and almost damage proof. My water tank has been in the sun for 5 years and looks like new - with no finish on it at all.

I agree with you.............:D
 
Sure there is a reason RV's have a (semi) wet wing tank... lighter and much less expensive.
Just like there is a reason other airplanes do have bladders or separate internal tanks (Cessna), and some have true wet wings (Mooney), and some have removable built up tanks like RV's (Piper Cherokee). All likely a result of different engineering decisions (you would have to ask them the reasons).
BTW, all of these other tank designs have also had their fair share of fuel tank problems. You can not assume RV fuel tank problems would be solved if they just had a different fuel tank design.

All of that I understand, and I agree, there is no perfect, leak-proof solution. On the other hand, the Beechs, Cessnas, and Pipers I've flown have never had a visible leak nor paint blisters, although I'm sure they probably had leaking tanks (like my C-150). I can only base my learnings on what I've experienced.

I guess what concerns me is that folks seem to be doing everything right X 2 and still ending up with leaking tanks and paint blisters. Doesn't seem to me that sticking with what we've got is the answer, especially if the only reason for doing so is that it's already been done that way 5,000+ times. There's always a need for a better mousetrap, especially when you have a very smart mouse! :rolleyes:

To be honest, at this point it probably does not matter for me, as I will be building my own tanks very soon, and most likely within a few years will be posting about my ruined paint job. I just wish I had other options. Unfortunately, there just do not appear to be any other immediately available options. Guess I'll just build them X 3 and hope for the best.
 
I agree with you.............:D
Im not sure what part you think is not possible about building a plastic tank. Structurally it would work. The tank could be blown with ribs or some other structural features that would make it easily as strong as the aluminum ribs - skin used now. It would take an engineer to run the numbers for thickness and material, but it would work. Weight is everything in an airplane and that would be the the problem to overcome. Maybe it would be worth one gallon less fuel to assure the tank wasn't going to leak.
I found this for $40. Includes senders and fittings.
20galtank.jpg
[/IMG]
 
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I guess what concerns me is that folks seem to be doing everything right X 2 and still ending up with leaking tanks and paint blisters. Doesn't seem to me that sticking with what we've got is the answer, especially if the only reason for doing so is that it's already been done that way 5,000+ times. There's always a need for a better mousetrap, especially when you have a very smart mouse! :rolleyes:

To be honest, at this point it probably does not matter for me, as I will be building my own tanks very soon, and most likely within a few years will be posting about my ruined paint job. I just wish I had other options. Unfortunately, there just do not appear to be any other immediately available options. Guess I'll just build them X 3 and hope for the best.

I don't disagree with the idea that we shouldn't continue doing something just because we always have, but it also makes no sense to make a change in the process just because, when we haven't been able to find any common thread related to the problem.

I realize this is a rather high profile issue (know one wants this to happen on their new airplane) but in reality, it is still a rather small percentage of flying RV's that have had this occur. I don't thank any builder should start out building their tanks already accepting the idea that the will have paint blisters in the future. The odds are actually very strong in favor of you not having the problem.

I wish I could give everyone a secret tip on what to do to prevent paint blisters (and I would if I new of one) but at this point there is no strong evidence of any one specific cause.
At this point, I am still leaning towards the changes that have occurred in paint formulations over the past 15 years or so as being a possible cause for some people and not for others.
One data point... Of the 5 Van's Aircraft demonstrators built within the past 12 years, that have the traditional wing tanks (I'm not counting the RV-12) have been painted with the exact same brand of paint.
Nothing special was done (at least compared to what many builders are doing lately) during tank assembly.
On 4 of them the paint used was Valspar 852 Sunthane, a single stage polyurethane. The 5th one (the RV-7A), was painted with a 2 stage base coat / clear coat
Of those 5 airplanes, two of them were built using Philippines assembled quick build kits.
None of these airplanes have ever had any paint blisters. The oldest of the 5 is the RV-7A
If anyone has used the Valspar Sunthane and experienced blisters on their fuel tanks, please get in touch with me.
 
Not Quite

...... I am still leaning towards the changes that have occurred in paint formulations over the past 15 years or so as being a possible cause for some people and not for others.......
This is where I must respectfully disagree with you Scott. So much has been written on this subject over the years. It is not that complicated an issue despite those who offer this theory or that, or those who confuse and dazzle us with their arcane technical knowledge of proseal. Proseal is tough forgiving stuff and it takes some doing to screw it up, but it MUST be applied correctly in the first place. An awareness of proper fay sealing and fillet sealing and encapsulation is absolutely essential. I continue to remain convinced that it is nothing more than improperly applied proseal that is the root cause of the blistering problem, nothing more. Some much conversation has elapsed over the years that the newbie who never so much as looked at proseal in his life until he built his first tanks or bought a QB is understandably confused. Certainly paint formulations have changed over the years, no one can dispute that. I maintain that if the proseal is properly applied in the first place, fuel or its fumes should not come into contact with newly formulated high tech paint in the first place.

Partly as a result of my urging, Dave Domeier built new fuel tanks heeding my technical advice. A year later he continues to report no paint blisters have occurred and I doubt that blistering will ever occur. The only thing that changed was his increased awareness and application technique.

All one has to do is review the graphic images in posts 100 and 163 in the famous paint blistering thread to understand how sloppy craftsmanship shouts out loud and clear as to the problem. Beside, the paint blistering problem has occurred for a long time, long before new paint formulations came onto the scene. Rerread this 1980 newsletter from the Pazmany folks regarding the vexing issue:
http://www.pazmany.com/newsletters/PL-1_and_2/64.pdf

No one likes to be told they are doing something wrong. Without proper training in the application of proseal it is a wonder even more cases of paint blistering have not cropped up.
 
... but at this point there is no strong evidence of any one specific cause.

Not entirely true, but certainly no specific proof.

At this point, I am still leaning towards the changes that have occurred in paint formulations over the past 15 years or so as being a possible cause for some people and not for others.

First a plausible theory, then development of experiments to prove or disprove. Can you offer a plausible theory, a reasoned chemical, mechanical or statistical basis for further investigation?

If anyone has used the Valspar Sunthane and experienced blisters on their fuel tanks, please get in touch with me.

The current blister database does include a Valspar single stage user, over Valspar epoxy. I will contact the builder and inquire about specific formulation, i.e. 852 Sunthane.
 
Partly as a result of my urging, Dave Domeier built new fuel tanks heeding my technical advice. A year later he continues to report no paint blisters have occurred and I doubt that blistering will ever occur. The only thing that changed was his increased awareness and application technique.

No one likes to be told they are doing something wrong. Without proper training in the application of proseal it is a wonder even more cases of paint blistering have not cropped up.

Just to keep the record straight, the first tanks on the 7A were QB (2002 era). The tanks I built last year were my first venture with pro-sealing - I did not build the original tanks. So far so good with the new tanks.

I thoroughly agree with Rick on his conclusion as to what is going on here with the blisters. With reasonable care and diligence with fay and fillet sealing the outcome will be OK. I did use Rick's method of clecoing the fay seal and letting the it cure for a day or so before riveting. Otherwise, the process was in accordance with the instructions in the build manual with no skimping on the amount of sealant used.

(a while back I went off on a tangent thinking excess MEK screwed up pro-seal but that simply is not true in that some builders thin the sealant with MEK and it cures fine - lately for non structural applications of the sealant, I have gone to mixing it to a pleasing color that looks right and it cures just like the stuff I weighed out. Pro-seal and Flamemaster are good products and it is difficult to not have it do its thing)



As has been noted on this thread and other threads on this subject, there have been many, many fuel tanks built by first time builders and they have not developed blisters. Take heart in this fact and press on! :)
 
This is where I must respectfully disagree with you Scott. So much has been written on this subject over the years. It is not that complicated an issue despite those who offer this theory or that, or those who confuse and dazzle us with their arcane technical knowledge of proseal. Proseal is tough forgiving stuff and it takes some doing to screw it up, but it MUST be applied correctly in the first place. An awareness of proper fay sealing and fillet sealing and encapsulation is absolutely essential. I continue to remain convinced that it is nothing more than improperly applied proseal that is the root cause of the blistering problem, nothing more. Some much conversation has elapsed over the years that the newbie who never so much as looked at proseal in his life until he built his first tanks or bought a QB is understandably confused. Certainly paint formulations have changed over the years, no one can dispute that. I maintain that if the proseal is properly applied in the first place, fuel or its fumes should not come into contact with newly formulated high tech paint in the first place.

Partly as a result of my urging, Dave Domeier built new fuel tanks heeding my technical advice. A year later he continues to report no paint blisters have occurred and I doubt that blistering will ever occur. The only thing that changed was his increased awareness and application technique.

All one has to do is review the graphic images in posts 100 and 163 in the famous paint blistering thread to understand how sloppy craftsmanship shouts out loud and clear as to the problem. Beside, the paint blistering problem has occurred for a long time, long before new paint formulations came onto the scene. Rerread this 1980 newsletter from the Pazmany folks regarding the vexing issue:
http://www.pazmany.com/newsletters/PL-1_and_2/64.pdf

No one likes to be told they are doing something wrong. Without proper training in the application of proseal it is a wonder even more cases of paint blistering have not cropped up.

I have never said blisters haven't been caused by poor workmanship. I know of tank blisters that have had fuel in them when punctured. It is pretty obvious those were caused by workmanship issues.

Where I think you are totally wrong Rick, ismaking the assumption that because evidence of poor workmanship has been detected, that that is automatically the cause of all paint blisters.
I am also well aware that tank blisters are not a new problem, but until more recently, they were a rather rare problem.

I will throw out a few questions of my own that I think need answers if we are ever going to solve this problem.

- I have been involved with RV construction for over 24 years. It is only in the last 5-7 years that paint blisters on tanks have become more than just an occasional occurrence ( BTW, all of the early instances I can remember all had wet fuel within the blister so it is obvious what the cause was).
So, considering that only in recent years have online forums made it possible for amateurs to get more educated about how to properly seal a riveted tank... Why weren't we seeing this through out the 90's when the volume of RV's being built really started to grow. Was everyone just lucky?

- I know of at least one instance where an owner contracted with a popular professional fuel tank assembler (who has probably built hundreds of tank sets by now), to build him a new set of tanks (his originals had lots of paint blisters). The new tanks were repainted by the same painter that had painted the airplane the first time (I assume with the same paint system, but I do not know that detail). The new tanks blistered.
Should we assume that the professional builder was less lucky than thousands of other amateur RV builders that have not experienced paint blisters on their tanks?

One other data point.. take it for what it is worth.
To date I have built or been directly involved with building at least 20 sets of RV fuel tanks.
On every one of those tanks, no special effort was taken in regards to proper fay sealing and fillet forming. I did not cover each shop head with sealant after setting. I did not use tank dimple dies.
What I DID do, was clean all parts very carefully (Naptha). Used a carefully applied layer of sealant on the rib flanges, and then was very careful inserting them into the skin so that no sealant was wiped/transferred from the rib, and clecoed as needed to develop a net fit of the rib to the skin. I then removed the sealant from the dimple depressions <gasp> before inserting the rivets, and set the rivets with the sealant uncured.

There has never been a leak or paint blister in any of these tanks.

I know this goes against standard practice, and I am not advocating that builders use this procedure. I am just offering it as another data point, to suggest that "just because someone hasn't used your recommended procedure, doesn't mean they are doomed to have paint blisters".

Was I just luck? (like the thousands of RV builders prior to paint blisters becoming a recognized problem). If so, I need to start spending my vacation time in Vegas.

Bottom line....
I don't disagree that some of the blistering has probably been caused by workmanship issues.
Where I do disagree, is categorically assuming that all of the paint blister issues up to this point could have been prevented by simply using the assembly techniques you advocate.
 
First a plausible theory, then development of experiments to prove or disprove. Can you offer a plausible theory, a reasoned chemical, mechanical or statistical basis for further investigation?

Actually, my theory is pretty much based on statistics. I don't have the smarts or education background to make any reasonable comments regarding chemical or mechanical factors. Some testing has been done by people who do have the smarts and background, but the results have so far been inconclusive.


The current blister database does include a Valspar single stage user, over Valspar epoxy. I will contact the builder and inquire about specific formulation, i.e. 852 Sunthane.

I would appreciate that information.
Along with any other details available pertaining to the painting process.
Such as the surface prep. and cleaning process used. Whether the primer was topcoated within the maximum specified amount of time (24 hours), etc.
 
Gentlemen, I appreciate this discussion, and to be honest it is making me feel better knowing that I may in fact build a tank that does not develop blisters.

I am curious if you believe that proper preparation of the metal could also be a contributing factor, although I'd imagine most builders do everything they can to prep the material properly. I see that naptha was used to clean the parts, and I was planning to use acetone or MEK, so probably same thing. I was also planning to scuff the surfaces well prior to cleaning. If there's anything else that you think is appropriate, please advise.

I'm hoping there will be other paint data published, but I'm not sure how the fuel or vapors could affect the paint unless there was first a failure of the proseal.

Anyway, thanks to you fellows for sharing your significant experiences. To us newbies this is one of the most challenging aspects of building an RV.
 
Folks have mentioned the posibility of changes in paint formula or changes in sealent formula-------what about changes in fuel formula???

What about a stackup of all of the changes????
 
I would appreciate that information.

Scott, it was Valspar Omega 2K HS, not 852 Sunthane 2K. No current listing on the Valspar site.

We read the same reports. I suspect the newer paints are more impervious at the vapor level, but I've not researched the matter. If so it would tend to increase the incidence of blisters, although it would not be the cause.

Known blistered paints currently include:

Valspar Omega
PPG Delfleet
PPG Concept
PPG Deltron
Jetglo
Stewart
Imron AF5000
House of Color
Dupont Centari
Dupont Chroma
Sikkens
 
Scott, it was Valspar Omega 2K HS, not 852 Sunthane 2K. No current listing on the Valspar site.

We read the same reports. I suspect the newer paints are more impervious at the vapor level, but I've not researched the matter. If so it would tend to increase the incidence of blisters, although it would not be the cause.

Known blistered paints currently include:

Valspar Omega
PPG Delfleet
PPG Concept
PPG Deltron
Jetglo
Stewart
Imron AF5000
House of Color
Dupont Centari
Dupont Chroma
Sikkens

Thanks for the reply.
 
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