What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

proseal/tanks sealant problems

R

rv72004

Well Known Member
The proseal on my lhs wing inner rib has gone totally sticky [can smear it off with a finger] after flying with a leaking tank for 2 months. The wings are quickbuilt and the inspection cover was leaking. Avgas has leaked onto the factory applied proseal on the bottom of the inner rib. [just below the cover]

I queried this with Vans and they said that the blue dye in avgas and oxygen cause the proseal to soften. I cannot argue with them, but they couldnt explain why this happened.
The proseal that did not have fuel leaking on it is ok.
I know I should have attended to the leak sooner, but flying was more important at the time. Had I known I would have taken care of it sooner.

What I still dont understand is why the proseal went totally soft. Can anyone explain ??

EJ
 
Are you referring to the fuel tank rib?

To my knowledge, there is no solvent for cured proseal, especially avgas. That's what it was meant to seal. It's amazing someone at Van's told you that. What did they suggest you do?

It sounds like the proseal is defective. Either a bad A-B mixture, a bad batch of proseal, or the shelf life had expired.
 
Gus at Vans said that there are no fuel fumes on the outside of the tank, so as the fuel drips onto the proseal, it evaporates and leaves the blue dye behind. This will lead to the proseal becoming soft and sticky and resembles uncured proseal. At least this is how I understand it.

I asked how its possible because it is a fuel sealer, and he said they are not quite sure.

Basically they say its my fault, [which I wont dispute as the inspection cover had weeped fuel for 2 months] ,but i still would like a technical explanation why this happened.[ie why the proseal softened]
Either way I have to sort it out.

It is the bead of proseal from the leading edge to the rear spar on the outside of the inner rib that has gone soft.

EJ
 
EJ,
Tom is right. The sealant was either mixed incorrectly or was bad to begin with. The military uses the same sealant in their aircraft and I've never seen Pro-seal, (B-1, B-2 or B -half, military equivalent) deteriorate once it's cured.
Charlie, Tucson AZ
 
EJ,

If I were you, I would call one of the sealant manufacturers and explain the problem to them. They could tell you if Van's explanation makes sense. If they tell you it is due to improper mixing or application, I would go back to Van's and see what they will do for you since they are quickbuild tanks. I'm not sure which product Van's uses for their quickbuld tanks, Flamemaster Chemseal or PRC Proseal, as they sell both, but you can reach Flamemaster at (818) 890-1401. All of the sealants are basically the same so you should be able to get a proper answer from any of the manuyfacturers.

Let us know what you find out.
 
I emailed Vans and asked them to find out from their proseal supplier why this happened. As soon as I get a reply I will post. Maybe I can save someone else the same hassle.

EJ
 
I have seen this before

I few years ago I was called by a local FBO to review and help repair an RV-4 that was recently purchased by an individual.

The brakes failed on landing and the owner brought the RV to the FBO. The FBO started looking over the RV and found several things wrong. One of which were leaking fuel tanks.

The tanks were removed and just as you described the Proseal along the inboard rib (bottom bead) was tacky. I too wondered why this could be. We scraped the old proseal off and applied new beads and replace the senders, flop tube and resealed the access covers.

The tanks were really built poorly. It looked like the original builder built the left tank thinking it was the right and the right thinking it was the left tank. So to fix the problem there were patches on the bottom of the tanks where the incorrect filler flange hole was cut. Also the outboard ribs had an access covers riveted on.

In general the who aircraft was a mess.

Paul
 
Paul,

These tanks were built by Vans and are perfectly done. Was the prc soft anywhere else or just at the bottom of the rib?

EJ
 
Wasn't mixed properly

Wasn't mixed properly




This was never mixed properly to begin with, (AVGASS DOES NOT BREAK DOWN PRC). What you see is prc that never set properly. This can happen when there is not enough hardener or the mix isn't properly mixed.

Solution: scrape the (never mixed properly) prc with a plastic scraper and fingernail, the best you can, and clean with lacquer thinner and properly mix some new prc and apply as required. The plastic bag cake decorating method in the preview plans works best.
Thoughrogh mixing of both components is critical and mix both components completely so they are one color, white streaks in the mix means not mixed enough. Mix by volume 15:1. No need to get anal about measuring weight. Then mix some more. Ok and some more. Get the idea! Also don't worry about expiration dates of the product no factor trust me. If using the tube just mix it thoughroughly no need measure.

If there are no other leaks, press on.
 
I've seen this on a re-seal job that was done on our Cessna Cardinal. I scraped it all out of our tanks and reapplied with new/good proseal. That is NOT normal, don't believe Van's on this one.
 
Vans has been promising to speak to their supplier to get me the facts. I have been patiently waiting for a answer ,but none yet. The clearly told me they mixed it correctly and that it was my fault it went soft.[fuel shouldnt leak on it]

I dont want to make a issue about it, but feel a bit short changed at the moment. Vans has always been great about sorting out issues. I wonder why they are avoiding this one ??
As I said before, if its my fault ,so be it. However everyone I speak to says its not, and Vans doesnt seem to agree.
What should I do ?
EJ

ps if I could figure out how to post pictures I could show how it looks.
 
Any result on this? The rv10 in am working on has had a fuel leak and the pro seal is all soft where the fuel has run on it. Going to drain the tank tomorrow and investigate where it is leaking. The plan was to clean it up and spread fresh pro seal over the area. The leak could end up being just the fittings. The pro seal is fine where the fuel is not on it, so it seams like vans could be right. Strange that that would be the case though.
 
I always buy prc proseal from acs

You get what you pay for. Vans is all about saving us a few dollars. I also used only 5052-O tubing.
 
After cleaning up the soft pro seal today, the only area that was soft was where fuel was running onto the pro seal and sitting. As soon as I got out of the blue stain area the stuff was fine. I do not see this as an improper mixture of the product as the area would have all been placed at the same time. The product deffinately does not hold up to fuel and air at the same time. Pretty strange as there are lots of this kind of a situation inside the tank, but never an issue I have heard of in there. I assume that the line of fuel and air is constantly changing so it does not have enough time to do anything. Not sure why the stuff vans sells would be any different than the prc that is sold elsewhere. The key, keep up your maintenance and inspect everything regularly. If you have a leaky fitting fix it ASAP. I am amazed at all the problems I am finding on this import.
 
So i wonder what is going on inside my fuel tank of the airplane i have sitting in my hanger for the past month unmoved, that is at the level line? Wouldn't this be the same problem?
Mike
 
mbetti said:
So i wonder what is going on inside my fuel tank of the airplane i have sitting in my hanger for the past month unmoved, that is at the level line? Wouldn't this be the same problem?
Mike
Click to expand...

Not flying for a month, your poor airplane.;) I wish I knew.


I may just test that. Put some pro seal on the side of container and pour fuel in so there is a line to the pro seal. Then check it every month to see if it starts to deteriorate the pro seal at the "line". Maybe it takes six months? Maybe it only does it of there is a small film of fuel weeping on it.:confused: I always liked science projects as a kid.
 
mbetti said:
So i wonder what is going on inside my fuel tank of the airplane i have sitting in my hanger for the past month unmoved, that is at the level line? Wouldn't this be the same problem?
Mike
Click to expand...

The inside of the tank probably has a lot more fuel vapor than oxygen. Could be there are not enough O2 molecules to support what goes on outside the tank when 100LL drips on the exposed sealant in an O2 rich environment, well at least relatively rich at 16-17%. It is much less inside the tank.

I've read the tech data supporting the tank sealant we use and it says nothing about its properties outside the tank. Inside the tank it is quite durable.

I have also experimented with "thinning" the stuff with MEK. It got thinner but as soon as the MEK evaporated, it was back to its original stiffness. I did not use it on the tank. I also figured out the stuff we use is Class B, designed to be applied with a gun or popsicle stick, it won't run or sag. The same product comes as a Class A which is a brush-able material... I am certain that is what was used building my QB tanks in 2002. It will run and sag.
 
There was a good bit of discussion about this particular issue, both here and elsewhere, back in 09. I'm not aware of any clear explanation.

Basics.....this from a very qualified individual who is not allowed to speak online:

.....the liquid pre-polymer molecules each contain 2 or 3 SH-groups (sulfur-hydrogen). SH groups in each molecule react in the presence of a peroxide (contains oxygen), split out water, and form an S-S bond (sulfur-Sulfur). This produces the chain extension or crosslinking. The curing agent (catalyst-accelerator) in the case of common aerospace sealants is manganese dioxide (MnO/2).

.....the following reference is suggested: Concise Polymeric Materials Encyclopedia, Joseph C. Salamone (ISBN 9780849322266)

A VAF contributor located a technical paper linking elastomer deterioration to peroxides. However, a careful read of the polysulfide sealant conclusions finds:

....From the available data it is uncertain whether catalyzel oxidation or acid catalyzed hydrolysis at the formal linkage is the primary degradation process. The latter mechanism is favored....

The manufacturer's rep discounted peroxides, but did report sensitivity to paint strippers.

Just of the heck of it I mixed sealant samples in correct and incorrect proportions. After cure, three samples were immersed in a 50/50 mix of MEK and lacquer thinnner. A fourth was immersed in ordinary drugstore 3% hydrogen peroxide. They've been there a long time now (since 11-16-09); none show any obvious change, certainly not reversion to goo. I am a chemistry idiot, so I'll leave conclusions, if any, to others. For sure 3% peroxide will reduce a new paint can to rust:

34gatzk.jpg


FWIW, there is no specification requiring the manufacturer to test sealant in avgas. The test fluid is called "JRF", for "jet reference fuel".

Nobody has ever offered evidence (a chemical process, physical mechanism, a measurement or test) to validate the "dripping avgas" theory. We can safely assume most of the avgas components evaporate, and thus concentrate the remaining component(s). That remaining component should be obvious if someone would simply hire a lab to run a softened sample through a GC/MS for comparison to a good sample.

Or you can debate a few more years ;)
 
Last edited:
I must agree. It is NOT a Proseal problem.
I had the same thing happen on my old 8. Where the leak was present for almost a year, the sealant became very sticky. Upon opening up the tank, ALL of the proseal on the inside was just fine. the only place it softened up was right where the leak was, so I have to Defend Vans on Their Answer.
Nordo
 
Last edited:
ASSUMING the tank seal used was MC 236-B2, the black part is oxygen accelerator. It speeds up the process of hardening the white part, which when EXPOSED to air would eventually harden on its own without the the black part.

Once the seal is hard oxygen or the lack of it does not soften it. Once hard, the accelerator or mix does not matter. This is not epoxy.

Vans statement that the dye without fuel attacks hardened seal could in fact be true. I doubt oxygen has anything to do with it. Oxygen is what cures the seal in the first place. Perhaps if you filled the tank with 100% blue dye used in Avgas all the seal would melt. The dye while suspended in 100LL might not be strong enough to attack.
 
Had some extra time this afternoon, did some searching....

The blue dye is 1,4 ? dialkylamino antraquinone. There are other interesting thngs in there too. Ok, chem majors, let's hear it.....

1imjyc.jpg
 
FWIW, I found the proseal in my Grumman AA5 tanks (which are similar to the RV design) had softened after 38 years of being soaked in avgas. The areas at the bottom along the inboard rib had softened to the consistency of modeling clay, and could be scraped off with a fingernail. This was only evident for about an inch from the bottom - above that it looked good. That is probably the only area that was always soaking in avgas, since it's probably near the limit level of useable fuel. Maybe only an occasional drying out is needed to prevent the problem?

Scraping and resealing fixed the leak.

Stan
 
splevy said:
FWIW, I found the proseal in my Grumman AA5 tanks (which are similar to the RV design) had softened after 38 years of being soaked in avgas. The areas at the bottom along the inboard rib had softened to the consistency of modeling clay, and could be scraped off with a fingernail. This was only evident for about an inch from the bottom - above that it looked good. That is probably the only area that was always soaking in avgas, since it's probably near the limit level of useable fuel. Maybe only an occasional drying out is needed to prevent the problem?

Scraping and resealing fixed the leak.

Stan
Click to expand...

FWIW............... is nothing.

Your tanks were NOT sealed 38 years ago with MC 236-B2. It was developed long AFTER your AA5 was built. MC 236-B2 was in fact developed by a chemist at Morton Thiokol.
 
DanH said:
Had some extra time this afternoon, did some searching....

The blue dye is 1,4 ? dialkylamino antraquinone. There are other interesting thngs in there too. Ok, chem majors, let's hear it.....
Click to expand...

A forum speaker at OSH a couple years ago said 100LL was formulated with 82 ingredients. His point being, alternate fuel from plant life would have 6-8 elements.

OK - so what IS causing the sealant to go soft outside the tank?
 
I wonder if this is just a Flamemaster sealer issue or does it happen with Proseal 890 also,,,what type sealer did you guys have the problem with? I used Flamemaster from Vans and had the same issue with the area of the leaks becoming soft. I have used proseal 890 (I believe it is a PPG product) on other aircraft for years and have never seen this problem. I believe both these sealers are Mil Spec 8802 sealers but there may be a difference in them.
 
You must log in or register to reply here.
Back
Top