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

David-aviator

Well Known Member
Six or seven reports been filed on another thread on the problem of paint blisters over fuel tank rivets. I sent a summary of those reports to Van's in an attempt to determine what is causing the phenomenon. This is an on going issue that started on my airplane over 2 years ago. I thought I was alone with the problem but that is not true as others are seeing the same thing.

I believe Van's would like to solve the problem but they do not have enough data points to begin an investigation. This was essentially where we left it 2 years ago. What follows is a response from Gus Funnel today on the subject.


We don't have any info on the subject other than what you sent
here. Be assured that if we had an answer, we'd let you know. I
realize that may not satisfy those who believe Van's knows the whole
story, but keeps it locked in a safe with the really good instructions
for the sliding canopy.

These are anecdotal reports, not data that can be analysed. The
paint types and methods of prep and application are mostly
unknown. It references only 6 airplanes out of 4700+ flying, so the
sample is very small. Not all the airplanes are QBs. I guess what one
would like to see is a common thread to distinguish these from other
RVs. I don't see that any conclusion can be drawn from what we
have here, other than that apparently < 0.2% of RV builders have
problems with paint on tank rivets.

Vans


If there are just 6 airplanes out of some 4700+ flying, we have a problem. If there are more, we need to know about it and the circumstances in an effort to determine what is causing it. So, if you've got blisters over tank rivets, please report it.

Thanks.

David Domeier
Troy, Missouri
RV-7A N707DD
 
Tank Blisters

David-aviator said:
Six or seven reports been filed on another thread on the problem of paint blisters over fuel tank rivets. I sent a summary of those reports to Van's in an attempt to determine what is causing the phenomenon. This is an on going issue that started on my airplane over 2 years ago. I thought I was alone with the problem but that is not true as others are seeing the same thing.

I believe Van's would like to solve the problem but they do not have enough data points to begin an investigation. This was essentially where we left it 2 years ago. What follows is a response from Gus Funnel today on the subject.


We don't have any info on the subject other than what you sent
here. Be assured that if we had an answer, we'd let you know. I
realize that may not satisfy those who believe Van's knows the whole
story, but keeps it locked in a safe with the really good instructions
for the sliding canopy.

These are anecdotal reports, not data that can be analysed. The
paint types and methods of prep and application are mostly
unknown. It references only 6 airplanes out of 4700+ flying, so the
sample is very small. Not all the airplanes are QBs. I guess what one
would like to see is a common thread to distinguish these from other
RVs. I don't see that any conclusion can be drawn from what we
have here, other than that apparently < 0.2% of RV builders have
problems with paint on tank rivets.

Vans


If there are just 6 airplanes out of some 4700+ flying, we have a problem. If there are more, we need to know about it and the circumstances in an effort to determine what is causing it. So, if you've got blisters over tank rivets, please report it.

Thanks.

David Domeier
Troy, Missouri
RV-7A N707DD

I have blister on the rivets of my tanks on RV7A slow build, Who do you suggest I report it to.
 
casper said:
I have blister on the rivets of my tanks on RV7A slow build, Who do you suggest I report it to.

Good question.
Kahuna started this thread with "Question on tank vent pressure at high speed", this forum.
Perhaps, to get things organized, we should tack the blister story to his thread answering the following questions.

1. Brand of paint and primer used.
2. Was the surface acid etched.
3. What cleaner was used to wipe down proseal.

Add anything that might point toward a cause of the gas out, extreme temperature swings, etc.

We need to identify a common element.

For example, my skins were acid etched and washed down before paint. For sure some acid came in contact with proseal at some of the rivet heads. We do not know what effect an acid etch would have on proseal, but if every airplane with the problem did an acid etch, it is a valid area to investigate.

There is a common thread. We need to find it.

dd
 
Just a thought: maybe solvent from the paint seeps into the tiny gap between the rivet head and the skin (if not filled with proseal), is trapped when the paint cures, then is heated by the sun and blows a bubble. For a bubble to grow there must be something to fill it under pressure.

Conor McCarthy
RV-9A 90990 fuselage
QLD, Australia
 
I did a QB kit and do not have any blistering on my tanks (or anywhere else). They have been painted for nearly 3 years. My plane is usually hangared, but has been tied down, outside, during trips out west and down south during hot summer months.

I prepped for paint using scotch brite to scuff the surface. No acid was used. I cleaned using laquer thinner, MEK, then finally Polyfiber Paint Cleaning Solvent C-2210. The exterior surfaces were primed with Polyfiber EP-420 white primer. The top coats were done using Polyfiber Aerothane (white and red).

It is very important to let any solvents gas out during painting. Let your epoxy primers cure for 7 days prior to top coating. Lightly scuff the primer coat with scotch brite and clean with C-2210 prior to topcoat.

This worked for me.

Roberta
 
Thank you for the post, Roberta.

This helps because we know what did not cause the annoying blisters.

I am wondering about the acid etch process. Not many people do it. Did any of the blister reporters use this process?

dd


robertahegy said:
I did a QB kit and do not have any blistering on my tanks (or anywhere else). They have been painted for nearly 3 years. My plane is usually hangared, but has been tied down, outside, during trips out west and down south during hot summer months.

I prepped for paint using scotch brite to scuff the surface. No acid was used. I cleaned using laquer thinner, MEK, then finally Polyfiber Paint Cleaning Solvent C-2210. The exterior surfaces were primed with Polyfiber EP-420 white primer. The top coats were done using Polyfiber Aerothane (white and red).

It is very important to let any solvents gas out during painting. Let your epoxy primers cure for 7 days prior to top coating. Lightly scuff the primer coat with scotch brite and clean with C-2210 prior to topcoat.

This worked for me.

Roberta
 
robertahegy said:
<Snip>

It is very important to let any solvents gas out during painting. Let your epoxy primers cure for 7 days prior to top coating. Lightly scuff the primer coat with scotch brite and clean with C-2210 prior to topcoat.

This worked for me.

Roberta

Hi Roberta,

very interesting, I have "read" that typically you need to topcoat the epoxy primers within 24 hours, before it Cures. By lightly scuffing I guess you recreate a key.

Regards
Rudi
 
Does anyone have pictures? This sounds like fuel leaking around the rivets to me. Very common on Mooneys, wet-wing Cessnas, Commanders, and especially Piper PA-28 series. Rivets will start to seep fuel, which bubbles the paint. If it goes on long enough, sometimes the bubbles will crack, and the blue dye will come out. Someone should cut the paint bubbles to see if there is fuel on the inside, if there is, the solution is to pull the tanks and reseal them.
 
Blisters!

Just discovered this problem on my plane a few weeks ago. Been flyin a little over a year. Quick build tanks. Kit serial number 81217. Only a few at this tme. Do not completely cover the rivet head in some cases, in fact, one starts at the edge of the rivet and migrates out. Busted one open about a week or so ago, no fuel from this cut so far. Seems to be another layer of paint or primer visible under the cut.
Other info to throw in the pot-
Three color paint scheme.
Washed wings with purple stuff, wiped down with prep solv before primer was applied.
Did not acid etch , but did use an etching wash primer.
Blisters are only in the red color on the tanks so far, not in the blue or yellow.
Blisters are only on top of the tanks.
Plane is hangered most of the time, but did spent some time outside a few months back, very hot at the time.
Rocket style fuel tank vents.
May try to get some pictures to post tonight.
 
Last edited:
Used Siken paint system.
COlor is DARK red
Did not use etching acid.
Normal scuff, wipe with MEK, then prep with 2 solutions provided by paint shop. Degreasers I believe.

I have cut a dozen of these blisters and there is no fuel, nor has there been any in the blister. No evidence of fuel ever being in the blister. And after sanding them off, no fuel vents out of the rivet.

I do think this is pressure related. Question for the physics buzzheads. If a 1/4" vent line goes 1' above the tank level, how much pressure builds up in the tank to get that fuel pushed up and out? I have never seen anything come out my vent line. My ventless caps are sealed tight with fuel lube on both the center o-ring and the outter big ring (I hate to see fuel streaming out of my cap on a full tank). Nothing ever vents out of the caps even when very full. So perhaps my very dark red paint heats up the air in the tank and creates pressure, not enough to push out the vent?

Talked to barefoot Billy earlier who just posted before me and he has the 'rocket' style vent tube curled in the wing root and dumping there. So maybe Im off base here. But Im still thinking this is tank pressure related.

Need answer on the tank pressure required to vent.
THanks
 
pressure

Well, water is 43.4 pounds per 100 feet so a one foot coloumn is .43 psi.

Av gas is about 2/3 the weight of water.

I estimate your one foot of fuel will create about 1/3 psi.

Mike
 
Theory??

After pondering this situation during my walk at lunch, I have come up with a theory. Throwing it out for discussion.
Here?s what I?ve seen mentioned-

1. Happens on the fuel tank rivets, not in other areas
2. Only seems to occur on the top surfaces
3. Seems to happen mostly on dark colors (which would see the most heat) but I think there have been reports on light colors also (which may have taken longer to develop?)
4. Only seems to be air in the bubble, no notice of fuel that I?ve seen mentioned
5. Doesn't seem to be a major pressure buildup in the tanks themselves, but does seem to be a pressure related problem

Okay, since the bubbles only have air in them, and we are not seeing any fuel come out of the bubbles once they?re opened up, is it possible air, or vapors of some type, for whatever reason, are being trapped in the dimple area of the rivet? This air, over repeated heat and cool cycles (expansion and contraction), is finally breaking the adhesive bond of the paint and forming these bubbles. While all areas are well prepped, because of the dimple, the area around the rivet doesn?t get the prep other areas receive, simply because you can?t get to it, you?re real careful in these areas, whatever. So the adhesive bond in this area could be weak and fairly easy to break loose. Why doesn?t it happen elsewhere? Because rivets in other areas of the plane are not sealed on the back side like the fuel tank rivets. They cannot build up this pressure.
Other questions do occur to me though. If this is the case, why do so few planes seem to have this problem? Could it be the chemistry of the new materials, or different materials, has changed or differs such that the flow is not the same, hence sometimes not flowing in these voids behind the rivet? Are people who put their rivets in wet having this problem? They would be the most likely not to have the voids.
 
Last edited:
Tank rivet blisters

I have been pondering this for three yrs. The only common thread here is tank sealer, When you get it figured out would you please tell me.
 
rvpilot said:
After pondering this situation during my walk at lunch, I have come up with a theory......... Are people who put their rivets in wet having this problem? They would be the most likely not to have the voids.
Interesting point. I wonder if specifications called out for the construction of the quickbuild tanks specifically include wet installing the rivets. If so, (and it should be) are the assembler/laborers who actually build the tanks always complying with the spec? How likely is it the contractor/vendor would freely volunteer such information? In a previous post I suggested drilling out an easily accessed tank rivet to visually confirm once and for all that traces of sealer exist around the countersink. If you do not find sealer traces in one countersink, chances are you may not find it in others.
 
Solvents expanding?

My ship is not yet painted nor flying, but last week, I was touching up some interior fuse pieces with Raldolph epoxy primer followed by PPG concept. In an attempt to harden the paint, I put the parts in a 170F oven for a few hours. I got bubbles! Some small, some larger, made the part look like it has poison ivy.

The paint had cured for over a week, the epoxy primer under it cured a week before I covered it with the PPG urethane.

When I picked off the bubbles (in disgust at the waste of my time...) I noticed that they were coming from under my recently applied touch up paint. It was paint that was a few years old and was rattle can stuff, not the epoxy primer. It was a rattle can automotive 'filler primer'.

Now, I thought that this filler was fully cured, which it must have been. Perhaps it absorbed some of the epoxy primer's solvents and did not fully out-gas them.

Could the proseal under the rivets be absorbing some of the paint solvents, thus, entrapping it? Then, the top coat goes on and hardens, not allowing any solvent to pass. Over time, the sun heats the metal, the solvents expand and since they cannot find any where to go, they expand and eventually bubble up the paint.

Just a thought.

Art in Asheville
 
Has anyone contacted the folks who make proseal and inquired about its ability to absorb solvents? Ooh, wait! I've got a nice idea: Get a nice glob of cured proseal, drop it into a measured quantity of solvent (I'd use urethane reducer) and let it sit for a bit, pull it out and see how much solvent remains in the beaker. Alternatively, put the glob on a gram scale before and after soaking. My money is on the theory that this stuff holds tiny amounts of paint solvent in the rivet dimple and then gives it back up once it gets heated. It's interesting to note that Roberta reports no problems, and that she took the somewhat unusual step of letting the primer cure before painting. Hmm. :confused:
 
Same issue

All,
My RV7A has been flying for 17 months, the first 5 months it was unpainted. The plane was painted last September by a high end quality shop. I've used them before on a Commander 114. We had a very hot spell in Michigan last month and I started to notice the same bubbles everyone is discussing. Only on the tops skins, none on the bottom. My wings were quick build.

My hanger mates? first flight in his unpainted 7A was in January this year. He had it painted by the same shop in April and is also seeing the same issue to a lesser degree.

Both planes are painted in Mattahorn white on the fuel tanks so the darker color issue doesn't apply. The paint shop will gladly strip the tanks and repaint the effected area but they want to have a good look to see what the issue is first. I'm to busy flying so the repainting will have to wait for later this year.

Gary
N715AB
 
Interesting commentary.

To summarize so far, it is not a quick built issue. The problem is occuring with slow build tanks also.

Paint color and heat probably are not an issue. My airplane is hangared with white tanks. The blisters first began on the bottom of the one tank, then the bottom of both tanks, then finally on the top of both tanks. This was progressive over a 2 year period. More rivets are now showing lifted paint than rivets still flat. The tanks have not been subjected to unusual heat or prolonged sun light except in flight.

It seems very logical that proseal is reacting with something used in the paint process. We need to illiminate acid etching. Has anyone had the blisters without acid etch?

Ater acid etch is scratched, and I think it will be, we need to focus on types of primers. i will find out what my painter used and post it in a few days.

David Domeier
RV-7A
Troy, Missouri
 
vent pressure

I have been told by an engineer that 2.3ft. of water colum is equal to 1lb.

Ted -4 finishing wiring.
 
Blister on tank rivets

I think Art in asheville is on the right track. As I said I have been pondering this for 3 yrs, can't stop flying to fix. I believe the tank sealer around the rivets is absorbing some thiner and does not gas out right away. As for as acid etch, I think you can scratch that. I did not acid etch, unless you consider self etching Mar Hyde as acid etching. On the my slow build 6 I used vynel wash, epoxy primer and matahorn white, NO problem. On my slow build 7 I used self etching Mar Hyde and matahorn white, Blisters on tank rivets. Mar hyde works but it is a short cut method and I would not do it again. That is my 2 cents worth. Hope it helps.
 
Kahuna said:
I do think this is pressure related.
If it was pressure related, I would expect the problem to be worse on the bottom of the tank. The pressure is the highest at the bottom when you pull g. The fact that it is only seen on the top of the tank suggests that it is heat related.
 
.......Could the proseal under the rivets be absorbing some of the paint solvents, thus, entrapping it? Then, the top coat goes on and hardens, not allowing any solvent to pass. Over time, the sun heats the metal, the solvents expand and since they cannot find any where to go, they expand and eventually bubble up the paint......
.....I believe the tank sealer around the rivets is absorbing some thiner and does not gas out right away.

While prudence certainly dictates nothing should be ruled out as a possible cause, I do find it difficult to reconcile the above thoughts with the fact that thousands of military and commercial jets.....many of which (for purposes including pressurization) have proseal under the heads of thousands of exterior fasteners including screws, hi-loks, jo-bolts, taper-loks, and rivets. And fasteners represent only a partial list of prosealed items because many parts are fay-sealed onto the exterior airframe and squeezed out sealer is simply painted over. If paint blistering was experienced on the skins of these aircraft, one would think engineers long ago isolated the cause and amended surface preparation to compensate.
 
Last edited:
Good call, Rick

Good call on the proseal deal Rick. I totally forgot that if there was something inherently wrong with the combo of proseal and paints the airlines would be hurting.

I'm out of theories for now. Perhaps another variable could be what was used as a clean up solvent during the tank build, different solvents breaking down the uncured sealant differently?

Art
 
Is it gasoline vapor pressure?

Since the blisters develop only over a few rivets, let's assume that there is sometning different about these rivets.

Could the difference be a pinhole in the proseal which is small enough not to leak gasoline due to its viscosity, but large enough to allow gasoline vapor to leak into the area around a rivet head, and eventually blister the paint?
 
Fuel Tank Rivet Blister

I noticed a single rivet on the top of the right tank was seeping AvGas (Blue) after I filled the tank the first time (QB Tanks). It was obviously lack of a good proseal around the rivet. I thought I had the seepage stopped using penetrating (green) locktite before it went to the paint shop but after about 10 hours of flying after painting I started to see a little AvGas seepage
around the same rivet even after painting.
 
Blisters on aft tank flange rivet heads

RV8 N842TL

AC painted summer '05. AC assembled and 1st flight 11/05. Blisters appeared late summer 06. Blisters only on rivets of aft tank flange both top and bottom; both tanks. 75% of the aft flange rivets. Similar quantity top and bottom. AC is QB. Prep was soap & water w/ scotch brite on sander for clean up, Alumaprep 33 acid etch then water rinse followed by Aladyne (sp) then water rinse. Northstar epoxy primer and sealer, then Northstar poly white, then poly colors, then clearcoat. Time between primer and color less than a week. Then less then 2 days for clear coat.

No blisters for a year. Noblisters anywhere else on AC, just on the line of rivets that fasten aft flange to tank skin. When cut open there is no trace of gasoline - no odor, no blue die or any other discoloration.

Question - who has repaired the blisters and how successful was the repair?

Tom Lloyd
Sandpoint, ID
posted 6/26/07
 
twlloyd said:
RV8 N842TL

AC painted summer '05. AC assembled and 1st flight 11/05. Blisters appeared late summer 06. Blisters only on rivets of aft tank flange both top and bottom; both tanks. 75% of the aft flange rivets. Similar quantity top and bottom. AC is QB. Prep was soap & water w/ scotch brite on sander for clean up, Alumaprep 33 acid etch then water rinse followed by Aladyne (sp) then water rinse. Northstar epoxy primer and sealer, then Northstar poly white, then poly colors, then clearcoat. Time between primer and color less than a week. Then less then 2 days for clear coat.

No blisters for a year. Noblisters anywhere else on AC, just on the line of rivets that fasten aft flange to tank skin. When cut open there is no trace of gasoline - no odor, no blue die or any other discoloration.

Question - who has repaired the blisters and how successful was the repair?

Tom Lloyd
Sandpoint, ID
posted 6/26/07
This is a twilight zone issue. As far as I know, No one has figured out why.
 
Me too...

Really glad I spotted this thread - wasn't aware so many were also having this problem.

For the record - for me only 2 blisters so far. Flown my RV-8 230 hours in the last 14 months since completion and no blisters until last month when the hot weather started. 2 blisters on the top of right wing tank only. In the silver section of paint (my leading edges are black - can't get any hotter than that in the sun - so forget about paint color).

QB wings, scotch brited wings, then cleaned with mineral spirits, then used etching epoxy primer (PPG), then dry and more scuffing with scotch brite and PPG single stage paint.

Popped a blister to check it out - no blue dye, no fuel, no nothing. Weird stuff.

I have forward facing fuel tank vents - stock location. My tanks were pressure tested and came out great with no leaks prior to final install.

Weird voodoo stuff going on.

-Rob
 
Funny its only happening to quickbuild tanks! There is a obvious problem that Vans is not recognizing. I have the same bubbles only on one tank. Also a leaking rivet which leaves a long blue streak.

Maybe one day I'll build a set of tanks myself.

O, yes, I also had the tank sealent go tacky on me. Vans said is was my fault as the cover was seeping slightly on the proseal. I redid all the factory sealant. I have tried to replicate my sealant going tacky like the factory one did. Been 3 months and it just doesnt .

O, well. Just one of those things I guess.

EJ
RV7
 
Not just QB Tanks...

Funny its only happening to quickbuild tanks!
Happened on Kahana'-8 and his were built from a standard kit. Mine were QB tanks, got a few of the blisters. I pin pricked them, no leaks. That was last summer. I have had no more come up since then, knock on wood!!
 
My QB tanks have been doing it for over 3 years....some new blisters noticed just recently. Most are bottom but top is catching up.
 
I'd like to throw the following points into this discussion:

1. I have noted Vans seems to have changed Proseal manufacturer/source over the years. First data point I would collect is detail of the manufacturer listed on the can. Clearly this is not relevant for QB tanks but for those who manufactured their own tanks it would be good to know.

Caution though - there are very few manufacturers but many companies repackaging the product for resale. It may be a bit difficult to determine the true origin.

2. Once a polysulphide (proseal) has cured it is extremely resistent to all solvents and is also very stable. It is unlikely that any solvents have penetrated the material, it is more likely to not be fully cured.

3. Various methods (materials) are used to harden the polysulphide and the curing rates will vary. I don't know the actual chemistry (I talk mathematics & physics only) but I will ask someone who does and see if there is some wisdom he can share. I suspect that with air excluded the cure may take longer than expected.

4. Being that this is being observed more frequently in quickbuilds it may be that the tanks are simply not sitting around for years before the paint goes on. The proseal is just not getting to full cure.

5. In the last 12-18 months I understand a new process is being employed for sealing tanks. IE the tanks is clecoed together with proseal, is left to go off for 24hours, then riveted. My guess is that the proseal remaining between the surfaces is thicker than was the case when tanks were riveted 'wet'. This larger volume may take longer to cure since there is more material trapped.

6. If you plan to test the ability of proseal to take up solvents do so by preparing some cured material, and weigh it very accurately. Immerse the material in the test solvent, and weigh again at periodic intervals. ASTN would help if you are serious about this test.

Doug Gray
 
Perhaps old cars can help us find the solution to the paint peel question

robertahegy said:
I did a QB kit and do not have any blistering on my tanks (or anywhere else). They have been painted for nearly 3 years. My plane is usually hangared, but has been tied down, outside, during trips out west and down south during hot summer months. Let your epoxy primers cure for 7 days prior to top coating. Lightly scuff the primer coat with scotch brite and clean with C-2210 prior to topcoat.
Roberta
Perhaps my old Chevys can help us find the solution to this dilemma. According to the Sherwin Williams primer data sheet, epoxy primer must be painted within 7 days or scuff sanded like Roberta did along with solvent. Failure to adhere to this rule will reduce adhesion between the next layer and the primer.

Second, on two properly prepared & painted 57 Chevs, the only place the paint gets weak and eventually lifts is behind the gas filler door which is actually a small doghouse that encases vapors rising from the vented gas tank. Within a year, the paint on virtually all 57 Chevs will weaken and peel off inside the gas filler door doghouse. The primer remains intact while the paint will peel off in layers.

My suspicion is the same thing is happening at the wing rivets which represent a weak seal for rising vapors. I suspect if the gas cap were left off the wing the vapors would rise out of the tank w/o seeking another exit. Of course, this is not a good solution.

Given that Roberta lives in cold country and her plane is hangared is also not a coincidence. Cold weather reduces vapor buildup and hangars eliminate sun heating of the wing & more vapor buildup. An occasional flight and parking in the sun may not be enough to induce the problem. If Roberta really wants to test her paint, she can loan me her airplane for six months and park it here in Tucson (hahahaha).

This thread is particularly timely for me because I plan to paint my 9 in the next few weeks. My plan will be to primer (after appropriately prep) and paint within 24 - 48 hours. That should promote adhesion between paint and primer and allow the two to latch into one another.

Perhaps other folks will offer comments on how to improve tank venting to reduce vapor buildup (my theory). One "crazy" idea would be to replace the gas tank caps with caps that allow vapors to rise but prevent rain and dirt from entering. Obviously, a big red flag to be attached to said caps so some nitwit doesn't fly off w/o replacing them first.

I welcome comments. Repainting each year is not acceptable and my plane will suffer the Tucson sun 7 days a week.
 
Its got to be Avgas or the proseal causing the bubbles. Nobody has ever complaint of blisters elsewhere.On the plane that is.
My opinion is that the factory doing the QB did not mix the proseal properly or used inferior product.
Avgas and heat are causing the bubbles.
Stop looking for the miracle cure or the paranormal cause. Buy quality milspec proseal and build the tanks yourself.
EJ
RV7
 
rv72004 said:
Its got to be Avgas or the proseal causing the bubbles. Nobody has ever complaint of blisters elsewhere.On the plane that is.
My opinion is that the factory doing the QB did not mix the proseal properly or used inferior product.
Avgas and heat are causing the bubbles.
Stop looking for the miracle cure or the paranormal cause. Buy quality milspec proseal and build the tanks yourself.
EJ
RV7

Mine was mil spec proseal, built myself. I got the bubbles.
I stripped the tanks of paint, put down an epoxy primer, and repainted.
Had about 40 bubbles in the summer of heat.
Now after rework above, I have 2 with the summer heat. ALl may reappear. I dunno. And the 2 I have are not on rivets where I had them before. Its bizzare.
 
rv72004 said:
Its got to be Avgas or the proseal causing the bubbles. Nobody has ever complaint of blisters elsewhere.On the plane that is.
My opinion is that the factory doing the QB did not mix the proseal properly or used inferior product.
Avgas and heat are causing the bubbles.
Stop looking for the miracle cure or the paranormal cause. Buy quality milspec proseal and build the tanks yourself.
EJ
RV7

I use mogas with alcohol.

The blisters are happening ONLY at rivets treated with proseal and in a fuel fume environment. Conclusion, whatever is going on involves proseal and/or fuel fumes. (would seem to be basic CSI 101)

I suggested long ago, a miss matched batch of proseal could be the problem but others state this is nearly impossible as the stuff always cures.(?) I have a difficult time accepting such a conclusion as any 2 part system of anything requires thorough mixing and at the correct ratio, whatever it is. Van's shot me down on this theory (there is no way their people in foreign lands could screw this up) and so have others on the forum.

I believe that when we move on the next world, we get answers to unanswered questions. I'm placing my bet on proseal as the problem. :)
 
I've been prepping and painting lately and have an observation. When you scotchbrite or sand the surfaces, minute amounts of residue accumulate in the tiny gaps around the rivets. A good etch and rinse removes it, but I wonder if it would be harder to remove on rivets that were prosealed in. I know zilch about chemistry, but I wonder if this residue embedded in this little teensy crevice might account for the problem.
 
Kahuna said:
Mine was mil spec proseal, built myself. I got the bubbles.
Tracking down an answer to a problem such as this can be maddening because quality control practices can and will vary from builder to builder. I am not convinced the problem can be traced to defective or poorly mixed proseal. Case in point. I am STILL using proseal to do the odd job on the project including fay and fillet sealing and plugging gaps in the assembly particularily as is called out to fume seal the firewall. That proseal expired in the early 2001 and I mix it by eyeball alone, judging what is a 10-1 ratio more or less. It always sets up as advertised. Certainly, I would not use expired proseal or rough guess the mix ratio when it comes to fuel tank construction, but I am saying that stuff is very forgiving of minor errors.

A common theme seems to be the blistering occurs only on those rivets associated with the fuel tanks.....and the blistering seems to be more common on quickbuild tanks. It is difficult to know exactly what production practices are in place overseas. I worked in a factory long enough to know that some workers can be casual or even dismissive about applying proseal per specification.

Has anybody actually peered inside a quickbuilt tank and verified the shop heads of the rivets are properly encapsulated in proseal? Has anybody drilled out a rivet on a quickbuild fuel tank and confirmed a trace of telltale proseal residue within its countersink?

Kahuna....you say you built the tanks yourself. Let me ask you this. Did you take the steps I just mentioned and as importantly....did you dab wet sealer around the countersinks before inserting and shooting the rivets? If you did...well I guess I'm back to square one along with everybody else.

fwdbaggage11415xl1.jpg
 
Last edited:
Rick6a said:
Kahuna....you say you built the tanks yourself. Let me ask you this. Did you take the steps I just mentioned and as importantly....did you dab wet sealer around the countersinks before inserting and shooting the rivets? If you did...well I guess I'm back to square one along with everybody else.

I did not dab on each rivet. BUT.. If proseal did not squeeze out from each rivet through the top skin on shooting it, it was drilled out and reset. I also line the rib and rivet after shooting with the stuff.
I have no answers... just questions.
Best
 
I did the loctite 290 thing that vans told me to do. The rivet is still leaking avgas .The bubbles are still there .

I feel a bit disapointed ,and dont know what to do next. O Yes, lets send a email to Vans. Keep you posted.

EJ
RV7
 
RV-7A Quickbuild Paint Blisters/Fuel Tank Rivets

I also have a problem with the Paint Blisters/Fuel Tank Rivets on both fuel tanks of my RV-7A quickbuild. I must have 15 blisters on each tank that just apeared this past week. The wings were Veri primed over a year ago and then kolar primer was applied a few months later and then painted with Imron white about 3 months ago. Does anyone have a fix for this. Am I going to have the same problem if I repaint the fuel tanks. Any help will be apprecited
 
discussion forum on paint over rivets??

n824rv said:
......and then painted with Imron white about 3 months ago. Does anyone have a fix for this. Am I going to have the same problem if I repaint the fuel tanks. Any help will be apprecited
IMRON is really tough stuff so if that popped...

IMO this deserves some kind of forum where ideas & data can be combined (Doug??). Within the two weeks I expect to be priming & painting (read lotsa $$$) so this subject is REAL interesting to me. My guess is venting but lotsa planes sit in the sun, few have this problem.

Barry RV9A wiring, paint, then bye bye Mother Earth. After 14 months, we're 30+/- days and a wake up till liftoff
 
QB Tanks

Just so happens that I am installing a flop tube in an existing QB tank. Here are some shots of the proseal and how it is applied. These tanks were received in the last 6 months.

These are pictures of the first internal rib after removing the outside rib.

img2365ie0.jpg
img2367kq9.jpg
img2366tb4.jpg

They looked OK to me but then look at the back of the rib I removed.
img2369cs4.jpg
img2370te3.jpg

See next post for internal pictures of sealed tank
 
MoreQB Tank

Here are internal and external shots showing the seal on the outside rib and its rivets.
img2379of2.jpg

img2378jr1.jpg

img2377ms1.jpg

img2375th5.jpg


Is it possible the proseal itself can outgas and cause these problems? The QB tanks seem to have it applied with a heavy hand.
 
jdeas said:
Is it possible the proseal itself can outgas and cause these problems? The QB tanks seem to have it applied with a heavy hand.
I am not at all concerned about the look of the proseal and while seemingly applied with a "heavy hand," it may not look pretty but will not cause anything other than additional weight.

I have had suspicions all along. In fact, I described those suspicions in a recent post to this thread and your detail photos tend to validate those thoughts. Good shop practice would have the builder encapsulate the shop heads of the rivets and I do not see that in your photos. You should not be able to see a shop head. I enclosed photos of a tank constructed a few months ago for comparative purposes. Notice that you cannot see shop heads as they are encapsulated by proseal. If the builder did not seal the shop heads adequately and/or did not seal the countersinks prior to shooting the rivets, it seems very plausible to me that fuel fumes can eventually find a migration route through unsealed rivet holes, especially since some pressure occurs within the fuel tanks.

Van's fuel tank instructions can be a bit ambigious. I quote from Section 7 page 7-7 in the RV-8 manual: "Dab a bit of sealant over every rivet head." Since the context was clearly addressing the inside of the fuel tank, it may have better read "Dab a bit of sealant over every SHOP rivet head."


img2367kq9edot6.jpg
img2379of2edbf1.jpg

fueltanks00815af3.jpg

fueltanks00815jj4.jpg
 
Last edited:
tank sealant

Another builder friend suggested the use of JEFFCO. Here is the Spruce description:

Jeffco 9700 is a 100% solids epoxy system which is the highest quality fuel and chemical resistant lining and coating material available. It contains no solvents and no corrosive or carcinogenic substances to assure low toxicity and ease of application. Provides superior low temp. curing, impact and abrasion resistance, and cures in the presence of moisture or humidity. Brushes on easily. Sold in 3 gallon kit containing 2 gallons of resin and 1 gallon of hardener. One 3 gallon kit can coat tanks of average size homebuilt. Used extensively on Lancairs and other homebuilts. Shelf life one year.

If it brushes on, it seems to me the $438 price tag could be split by several builders whose only usage is to brush the stuff inside the tank along the top of the tank where the rivets are.

Thoughts?

Barry
 
The great mystery

Kahuna said:
I did not dab on each rivet. BUT.. If proseal did not squeeze out from each rivet through the top skin on shooting it, it was drilled out and reset. I also line the rib and rivet after shooting with the stuff.
I have no answers... just questions.
Best

Does the above statement mean that you applied Proseal to each rivet shop head after it was set ie if one were to look inside your tanks there would not be any rivets showing at all. Is that what you mean.
 
Back
Top