Paint Blisters/Fuel Tank Rivets

[mike newall]

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

[scsmith]

Originally Posted by rvbuilder2002

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.

[rocketbob]

Originally Posted by scsmith

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.

[Mel]

Originally Posted by rocketbob

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.

[rocketbob]

Originally Posted by Mel

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.

[FORANE]

Originally Posted by rocketbob

blisters don't occur on the bottom side.

They did on the RV-9A I owned; top and bottom had blisters.

[rocketbob]

Originally Posted by FORANE

They did on the RV-9A I owned; top and bottom had blisters.

Mine didn't as it was rare that I parked it for an extended period without filling the tanks first.

[BillL]

Originally Posted by Huskyhipdoc

https://www.dropbox.com/s/3e3khte17h...0991.jpeg?dl=0
https://www.dropbox.com/s/15ytz90ram...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.

[DanH]

Originally Posted by Huskyhipdoc

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?

[ColoCardinal]

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!