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Paint Blisters/Fuel Tank Rivets

Go to Hobby Lobby - look in the bracelet/trinket/bangle section and look for tiny, tiny discs.

They are for either bracelets or rings. Made out of copper but plated.

I bought a bag of tiny ones for a dollar or so. Trim the ring tag off, flat it down with 320 paper and put a weeny blob of epoxy on and stick over the offending rivet.

When set, wet and dry over to remove edges and then prime and touch up.

Move on, fly on :D:D
 
Interesting theory, but when testing the theory we need to consider that the vent design originates all the way back to the RV-4. There are 1000's of RV's with this design, many of them completed in the 80's and 90's with (as far as I am aware) no history of paint blisters.
It has only been within the past 10 years or so that they have been occurring.
My theory is that it is at least in part related to the EPA driven formulation changes that have occurred in paint systems over that time, but that is just a gut feeling.... I don't have any more evidence to back up that theory than any of the others that have been suggested up to this point.

This theory doesn't explain blisters under vinyl wrap.

Might be changes in formulation of the ProSeal though.
 
This theory doesn't explain blisters under vinyl wrap.

Might be changes in formulation of the ProSeal though.

I've been saying for years its the in-fuselage loop in the vent lines that causes paint blisters. Slug of fuel in the loop puts enough pressure in the tanks to cause outgassing via imperfections in the sealant around rivets.

Many certified aircraft that are non-strutted have a vent line that extends to the tips via a Dukes flapper check valve with a small hole drilled in the body of the valve. This does two things: 1. allows for venting even when parked on a sloped surface and 2. Drains the vent line back into the tank to prevent the slug of fuel from increasing pressure in the tank.

I've never seen blisters on wet-wing airplanes, other than RVs.
 
I've been saying for years its the in-fuselage loop in the vent lines that causes paint blisters. Slug of fuel in the loop puts enough pressure in the tanks to cause outgassing via imperfections in the sealant around rivets.

I can't quite buy that theory since, as Scott says, there are literally thousands of RVs built between the late '70s and the mid 2010s per the plans without a single blister.
 
I can't quite buy that theory since, as Scott says, there are literally thousands of RVs built between the late '70s and the mid 2010s per the plans without a single blister.

Variations in proseal thickness can explain it, as well as the fact that blisters don't occur on the bottom side.
 
https://www.dropbox.com/s/3e3khte17hq68ld/IMG_0991.jpeg?dl=0
https://www.dropbox.com/s/15ytz90ramxmz9u/IMG_0992.jpeg?dl=0
Abject despair today... then I found this thread..

2018 QB wings, cleaned with detergent degreaser, wiped down with MEK, then two-pack acid etch primer (P30B) left for 24 hrs then two pack epoxy primer (PR143).
Pressure testing of tanks was fine.
I had 20 litres avgas with fluorescent marker in the tanks for a week with no leaks, then the tanks drained fully and left open for 24 hours, and then the wings stored vertically (leading edge down) with the tanks fully sealed to prevent critters getting in.
Today, I moved the wings and one is fine, the other has 10 blisters, 9 on the lower aft flange and one on a rivet one place closer to the leading edge.
No top coat, and minimal fuel exposure yet Ives still got blisters!
I sanded them all down and obviously no fuel present under them.
Irritating beyond belief, but at least ive found them before spending $10k on a paint job.
So how do I fix the problem? epoxy over the rivets, fibreglass tape and filler?
I feel like setting fire to the bloody thing at the moment! I dont mind sorting out my own ****-ups, but sorting out the result of a "professional' build is maddening!
Darren, if it were me, after calming down a bit . . . I test the primer adhesion. Take a piece of strong adhesive tape, apply to the painted surface and slowly peel it off. Test the tank in several places for adhesion of the primer. The prep did not mention abrading the surface before the process. ;) Do the adhesion test over the rivets on the tank and some other non-tank rivets too. This is just to eliminate some possibilities contributing to the blisters, some that one might be able to control. If everywhere but the blister areas pull no paint, then your process is sound and the issue is focused on the pro sealed rivets.
 
Today, I moved the wings and one is fine, the other has 10 blisters, 9 on the lower aft flange and one on a rivet one place closer to the leading edge.

Was the surface with blisters exposed to direct sunshine, or a radiant heater, or a similar heat source?
 
paint blisters

I can't quite buy that theory since, as Scott says, there are literally thousands of RVs built between the late '70s and the mid 2010s per the plans without a single blister.
Is it possible that only planes painted with catylized paints or "wrapped" are at risk for this? Both are less permiable than the older enamel paints of the past.
As a 25+ year owner of a Cessna Cardinal, I will second Bob's observation that, I too have never seen one with rivet blisters. Could it be that they use a different sealant in the tank?
Very puzzling, indeed!
 
My RV-10 was commercially painted and has a few bubbles on the top tank rivets within a few months. It was built in 2011 and first painted in 2017. It is a slow build plane.
 
Is it possible that only planes painted with catylized paints or "wrapped" are at risk for this? Both are less permiable than the older enamel paints of the past.
As a 25+ year owner of a Cessna Cardinal, I will second Bob's observation that, I too have never seen one with rivet blisters. Could it be that they use a different sealant in the tank?
Very puzzling, indeed!

Back in '84 I purchased a '68 Cardinal which had recently been over painted with DuPont Imron. It was fine until I started running MoGas (pre-ethanol mandate) blisters galore soon appeared on the top surface of the wing tanks.

Moved on to a '75 Cardinal RG in '93 with good original paint, only running AvGas, not one blister. I had it stripped, primed, and repainted in '10 with JetGlo. No blisters to date.

I purchased my '80 RV-3 about 18 months ago and have only run AvGas since I've owned it; no blisters. One interesting note; my RV was owned by Sun 'n Fun for about 15 years and I'm sure the tanks set dry during this period. I think I'll stick with AvGas based just on my personal experience.
 
I built a RV-6 and sealed the tanks with PRC 1422, using the B class for the fay seal, and fillet seal covering the tails with this material. In addition, I overcoated with the A class as a brush application and used this grade for wet setting the rivets. The paint is Imron. No bubbles, no leaks or mushy sealant after 26 years.

The airplane I own now was done with the Chemseal product CS3204, which is qualified to Mil-S-8802 Type II. I did not do this airplane myself, but am sure of the sealant used. After 10 years it has bubbles, and the sealant around the fuel sender plates is mushy and seeping. There is a significant difference in the 2 sealants which was introduced in or around the early 90's. At that time the Mil spec was revised to delete dichromated sealants. PRC 1422 used to be an Mil-S-8802 Type II qualified sealant but the change to the standard caused it to be dropped as a qualified material. PRC had PRC 1440 to take the place of PRC 1422 with respect to the Mil qualification. I had documented this in an article in Sport Aviation back in the late 90's. I am not sure how the Proseal line migrated, and was unfamiliar with Chemseal back then. There were tons of Cherokee tanks sealed in the aftermarket with PRC 1422 and I don't recall blistering as a problem. I am wondering if the change to the sealants has resulted in the current crop of problems. If anyone else has used PRC 1422 instead of either PRC 1440, PS 890 or Chemseal 3204 and has bubbles speak up.

Courtaulds Aerospace (PRC) PRC 1422 - dichromated no longer Mil qualified. PRC 1440and PS890 are Mil-S-8802 Type II qualified- dichromates replaced with maganese.

CHEMSEAL CS-3204 is Mil-S-8802 Type II qualified maganese based.

The products have clear differences from the application standpoint. If you mix up both they have some differing properties. I am sure there are smarter chemist type here that might recognize what effect the replacement of the dichromates with maganese might do to the sealant with respect to resistance to Avgas.
 
I built a RV-6 and sealed the tanks with PRC 1422, using the B class for the fay seal, and fillet seal covering the tails with this material. In addition, I overcoated with the A class as a brush application and used this grade for wet setting the rivets. The paint is Imron. No bubbles, no leaks or mushy sealant after 26 years.

The airplane I own now was done with the Chemseal product CS3204, which is qualified to Mil-S-8802 Type II. I did not do this airplane myself, but am sure of the sealant used. After 10 years it has bubbles, and the sealant around the fuel sender plates is mushy and seeping. There is a significant difference in the 2 sealants which was introduced in or around the early 90's. At that time the Mil spec was revised to delete dichromated sealants. PRC 1422 used to be an Mil-S-8802 Type II qualified sealant but the change to the standard caused it to be dropped as a qualified material. PRC had PRC 1440 to take the place of PRC 1422 with respect to the Mil qualification. I had documented this in an article in Sport Aviation back in the late 90's. I am not sure how the Proseal line migrated, and was unfamiliar with Chemseal back then. There were tons of Cherokee tanks sealed in the aftermarket with PRC 1422 and I don't recall blistering as a problem. I am wondering if the change to the sealants has resulted in the current crop of problems. If anyone else has used PRC 1422 instead of either PRC 1440, PS 890 or Chemseal 3204 and has bubbles speak up.

Courtaulds Aerospace (PRC) PRC 1422 - dichromated no longer Mil qualified. PRC 1440and PS890 are Mil-S-8802 Type II qualified- dichromates replaced with maganese.

CHEMSEAL CS-3204 is Mil-S-8802 Type II qualified maganese based.

The products have clear differences from the application standpoint. If you mix up both they have some differing properties. I am sure there are smarter chemist type here that might recognize what effect the replacement of the dichromates with maganese might do to the sealant with respect to resistance to Avgas.

Interesting - I was reading some book preview on polysulfide sealants (Properties and Applications of Elastomeric Polysulfides
By T. C. P. Lee) and it mentioned that the aerospace versions used dichromate but I looked up the SDS for chemseal and it showed manganese in the hardener. The book also talked about reversion in some formulations , but not the dichromate version. (another failure mode we have seen) I am most certainly not a chemist, but did notice the ingredients. Thanks for sharing. I see the PRC-1422 is available at SkyGeek.
 
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Do note that there isn't any evidence of correlation between reversion and blisters, and blistered rivets have been sectioned and inspected closely. I'm inclined to think they are separate issues.
 
Do note that there isn't any evidence of correlation between reversion and blisters, and blistered rivets have been sectioned and inspected closely. I'm inclined to think they are separate issues.

Right, Dan, those are separate failure modes and did not mean to imply they were linked.

Hey - just saw a post about Vans -14 demonstrator having rivet blisters. Someone take a picture at SnF so the evidence won't get lost!!

I wonder if helium in the tank will show the leakers before paint??
 
My brother and I have a quick build -7A. It is thirteen years old. We have had two blisters appear on one tank and one on the other.
 
Has there been any resolution to this issue? Is MS involved? I received my QB wings in 2014, finished the build in 2019, painted in 2020, 300 flight hrs later the tanks are littered with bubbles. Many of them. It looks terrible.
 
This is a never ending story - but wait there is more

This is a never ending story - but wait there is more.

An RV7 owner phoned me with the following story:- I got someone in to polish my RV7 with no blisters and no leaks on the tanks. RV7 was imported from the USA about five years ago.

First fuel uplift after the polish and it is leaking from many rivets top and bottom. He asked my advice and after weighing up the options the call was made to remove the rear tank baffle by someone he trusts at a sheet metal shop.

Please tell me what has happened here with these tank ribs - there were no visible damage on the outside. They seem to be seriously compromised and bent.
 

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This is a never ending story - but wait there is more.
v
An RV7 owner phoned me with the following story:- I got someone in to polish my RV7 with no blisters and no leaks on the tanks. RV7 was imported from the USA about five years ago.

First fuel uplift after the polish and it is leaking from many rivets top and bottom. He asked my advice and after weighing up the options the call was made to remove the rear tank baffle by someone he trusts at a e sheet metal shop.

Please tell me what has happened here with these tank ribs - there were no visible damage on the outside. They seem to be seriously compromised and bent.

This is such peculiar damage, I can not imagine how and one wonders if it was during the installation or if it has happened after.
 
This is such peculiar damage, I can not imagine how and one wonders if it was during the installation or if it has happened after.

Well that makes two of us
 
Paint blisters

Hope this is helpful.

After roughly 3 years since N80WN (RV7) was painted blisters have started to appear. (Sept 15) ALL are on rivet heads associated with gas tanks. Entire plane was primed prior to paint. No blisters any where else. Plane was QB. 300 + hours. Always hangered. Any thoughts?

Will post photos and research specific aviation paint type ASAP.
 
Hope this is helpful.

After roughly 3 years since N80WN (RV7) was painted blisters have started to appear. (Sept 15) ALL are on rivet heads associated with gas tanks. Entire plane was primed prior to paint. No blisters any where else. Plane was QB. 300 + hours. Always hangered. Any thoughts?

Will post photos and research specific aviation paint type ASAP.
Many have reported this issue and I believe it is still u known as why.
I have my plane painted, now it has been 5 months, and anxiously waiting to see if blisters will show up, none so far.
 
After roughly 3 years since N80WN (RV7) was painted blisters have started to appear. (Sept 15) ALL are on rivet heads associated with gas tanks. Entire plane was primed prior to paint. No blisters any where else. Plane was QB. 300 + hours. Always hangered. Any thoughts?

When were the tanks built?
 
This is a never ending story - but wait there is more.

An RV7 owner phoned me with the following story:- I got someone in to polish my RV7 with no blisters and no leaks on the tanks. RV7 was imported from the USA about five years ago.

First fuel uplift after the polish and it is leaking from many rivets top and bottom. He asked my advice and after weighing up the options the call was made to remove the rear tank baffle by someone he trusts at a sheet metal shop.

Please tell me what has happened here with these tank ribs - there were no visible damage on the outside. They seem to be seriously compromised and bent.

Anyone else think localized heating from the polishing process may be a factor ... ?
 
No, it is from collapse that was induced by the air pressure delta caused by the tank vent being plugged. It has been seen before.
This may very well be the case for this set up of tanks but many have reported, including myself for the last two planes that fuel tank rivets show paint blisters which was not as a result of vent being blocked.

I am waiting to see if my new plane will show the same thing.
 
I didn't say anything about paint blisters being caused by a blocked tank vent.
The comment was related to an earlier post showing crushed nose ribs in a tank. They were caused by a blocked vent.
https://vansairforce.net/community/showpost.php?p=1623889&postcount=420



This may very well be the case for this set up of tanks but many have reported, including myself for the last two planes that fuel tank rivets show paint blisters which was not as a result of vent being blocked.

I am waiting to see if my new plane will show the same thing.
 
No, it is from collapse that was induced by the air pressure delta caused by the tank vent being plugged. It has been seen before.

Hi Scott and others - my apologies for not reporting back. I have personally checked the vent lines - no blockages there. The owner has finally shared what has really happened. He had a puncture in a remote place and his son shoulder lifted the RV form underneath the tank and not on the spar. Expensive mistake :eek:

Years ago I have experienced it while test flying a new RV10. I looked at the left wing and saw how the panels were sucked in between the tank ribs. The FP was still good and I switched tanked immediately. No damage and the source of the problem was a piece of tank sealant blocking the opening of the vent line. It was a QB tank.
 
QB Tank bubbles - Poorly sealed rivets acting like 1 way valves ?

Hi All,

Had the same issue with both my QB tanks, over 20 bubbles on both sides, some are leaking fuel.

Wrote to Vans and got a reply saying its my fault for not priming or painting the tanks properly.

I can see that some QB and self SB tanks have this problem. Some owners have opened up their QB tanks and found deficiencies in the sealing of them.

I have built 2 sets of SB tanks, I am paranoid about sealing so lots of proseal on every shop head and in every fillet. 5 years later, not a single bubble.

I think this is a manafacturing issue. I think that the inadequately or insufficiently sealed rivets are acting as 1 way valves. Because of the shape of the rivet head, and the lack of enough proseal, a tiny amount of fuel or vapour is getting out, it becomes trapped between the paint and the rivet head and now cannot get back in to the tank. As the day warms up the vapour exerts pressure, lifting the paint up and causing a bubble. at night the vapour cools, but the space of lifter paint has now increased, allowing for more vapour to collect, and so the cycle continues and the bubbles get bigger, until they split and then stop growing because the vapour can now escape.

Leak testing the tanks is pointless because the leaks are micro tiny, probably too small to detect without specialist equipment. Stripping and repainting them with a more adherant paint or an epoxy will help but thats a lot of work and extra expense, and a band aid to fix a faulty tank, with no guarantees it won't form more bubbles in the future.

Maybe I will try cutting them or perforating them and see if that stops them growing. But my money is on a micro fuel leak from inadequate sealing in the first place, not on a paint reaction as Vans says.

What do you think?
 
I haven’t read through the 44 pages, but I have built 4 sets of tanks over the years.
One thing that has always perplexed me was the advent of “tank dies” and the concept of filling the manufactured head side of the joint with proseal.
Both of these things will weaken the joint.
Proseal under the head of the rivet in particular seems to be a very plausible mechanism for paint blisters.
People solvent wipe their skins to clean and prep for paint and I can easily see that resulting in gassing off over time even without an actual leak.
 
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