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My cured Pro-Seal has turned to goo!

ArVeeNiner

Well Known Member
So, I finished my fuel tanks back in August of 2004. They have had fuel in them since my first flight back in May of 2012.

A little over a year ago I noticed a small fuel seep at the inboard end of my left fuel tank. It was very small and so I worked on other minor issues first...until today.

I pulled the tank and noticed that the Pro-Seal in the vicinity of the leak has turned to goo. It has the consistency of uncured Pro-Seal.





I don't know if the fuel caused the Pro-Seal to turn to goo or vice versa. I find it doubtful that fuel caused it to turn because resistance to fuel is the whole point of Pro-Seal.

Maybe I got the mix ratio wrong but in all areas but the area where the leak occurred, the sealant seemed to cure just fine, including areas adjacent to the leak area. The right tank has no leaks at all.

I only found goo at the bottom of the rear baffle and the bottom of the end rib. All goo locations are external to the tank.

Has anybody else ever seen anything like this?

As far as the repair, I'll clean off all the bad sealant and re-apply. Also, I'll put a large fillet in the area of the leak inside the tank. Here is a shot of the rear baffle from the inside. It looks a bit light on sealant:



Here is the inside corner. This is where I suspect the seepage occurred:



Sound reasonable?
 
Likely, a mix issue

I have worked with Proseal and other similar sealants often at my day job over the last 35 years, and this does occasionally happen when during the mix, a pocket of the curing paste is not mixed in fully. We now use power mixers which helps, but if you have other areas that are fully cured with no problems, I suspect this may be what happened in your case.
 
I agree with Bill that it was most likely a mixing issue. I have a heated temperature controlled epoxy cabinet in my shop from building a Cozy MKIV, so I kept my Pro-Seal in the cabinet during the tank builds. Kept at around 110* IIRC, the Pro-Seal is very EZ to work with and mixing in the hardener was a breeze.
 
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Very common (search the forums), and yes I have seen it many times.

Tank sealant will act just like yours did if it has a prolonged exposure to being constantly whetted with fuel, and a source of oxygen.
 
Very common (search the forums), and yes I have seen it many times.

Tank sealant will act just like yours did if it has a prolonged exposure to being constantly whetted with fuel, and a source of oxygen.
Do you mean very common if the sealant was not mixed properly or do you mean that it happens very often even with properly mixed sealant?
 
You described exactly my thoughts when it happened to me (goo) #4 post and the factory will tell you the same thing. Use paint thinner,acetone, or any number of bad chemicals with a small wire brush and a plenty of elbow grease. Remove any pro seal that has blue stain not just the gooy part it has been effected also. I learned the hard way had to go through this twice. Mix well new batch of pro seal and apply liberally.
Good luck
G.P.
 
Do you mean very common if the sealant was not mixed properly or do you mean that it happens very often even with properly mixed sealant?

I mean that it is common in a situation where a leak has been allowed to continue for an extended period of time and sealant has been constantly whetted with fuel.
It has nothing to do with how the sealant was mixed.

There is no oxygen inside a tank that contains fuel. Fuel vapors are heavier than air.... they displace the oxygen. Different story on the outside of the tank.
 
Very common (search the forums), and yes I have seen it many times.

Tank sealant will act just like yours did if it has a prolonged exposure to being constantly whetted with fuel, and a source of oxygen.

OK, let's split a few hairs here - how much oxygen? The interior of the tank has lowered oxygen due to the vapor pressure of the fuel. That is why the free space in a gasoline tank won't support combustion, oxygen ratio t fuel is too low. So how low is needed for pro-seal to retain it's properties i.e. not turn to goo?

The interior is wetted, but not constantly evaporating, like a small weep, so is a weep necessary for the exterior to have deteriorated? Or did this begin from the interior?

What are the bench/lab validation results for dipping in fuel, what are the quantified acceptable parameters for long life?

Depending on the answer -the question is - will ALL tanks eventually have leaks at the top where the fuel does not touch when parked?
 
Depending on the answer -the question is - will ALL tanks eventually have leaks at the top where the fuel does not touch when parked?

No, or thousands of RV's would now be leaking (and that is not the case).

If there is a leak or seep where sealant is always being exposed to evaporating fuel, the sealant will become soft.

If you want to know the chemistry explanation you will have to contact the sealant manufacturer, but they will tell you the same thing
 
Thanks everybody. It seems like this is a normal phenomenon and maybe not the result of an improper mix ratio. Who knew?

I'm in the middle of cleaning up all the soft stuff and fuel and should have ample amounts of new sealant in place in the interior of the tank in the next day or two. I'll also lop some more on externally just for good measure.

Thanks again!
 
There are a lot of variants of "Proseal". At least 3 different manufacturers and 2 or 3 varieties for each manufacturer. What stuff are you using on the fuel tanks?
 
What are the bench/lab validation results for dipping in fuel, what are the quantified acceptable parameters for long life?

There are no standards specific to 100LL exposure. All the standard tests use JRF:

http://standards.sae.org/air4275/



If you want to know the chemistry explanation you will have to contact the sealant manufacturer, but they will tell you the same thing

Oddly enough, a few years ago my contact at Flamemaster said he knew nothing about it. Mind getting the full explanation for us?
 
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Oddly enough, a few years ago my contact at Flamemaster said he knew nothing about it. Mind getting the full explanation for us?

Dan, I have not ever personally talked with anyone at Flame Master about this, but in response to people inquiring with tech support regarding this issue, at least someone at Van's has.
Since I have seen it numerous times (once a very mild case on my own airplane), and the word that someone at Flame Master acknowledged it can happen, that has always been enough information for me.

They way I look at it... I don't need to know why.... I just need to know to always be inspecting for fuel leakage, and then fix it as soon as it is detected.
 
Dan, I have not ever personally talked with anyone at Flame Master about this...

Sure, sure, but you know how it is...sometimes a vendor will honor a request from an OEM when the rest of us poor schlubbs get blown off. Yet, the schlubbs, being dedicated to education and recreation like we are, would really like to know the chemistry. You could ask 'em to write it down for us, and then post it here. That would be great.

BTW, oxidation is a maybe, but I soaked a cured sealant sample in 3% hydrogen peroxide nearly 4 years without softening. It did eat the metal can.

And I recently examined a softened polysulfide sealant sample taken from inside a tank. It wasn't fully reverted (more like not very sticky week-old chewing gum, or old-fashioned window glass glazing putty), but certainly not normal-as-cured. The owner removed the rivets and easily peeled the skin off the ribs. Samples from the top of the tank (vapor/splash exposure) and the bottom of the tank (submerged exposure) were similar. Samples of the same sealant from outside the tank (zero fuel contact) were solid/normal. Built circa 2005, sealant brand unknown; checking now.

Postscript: Sealant was Chem Seal (Flamemaster) 3204-B....same stuff common to RVs.
 
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Maybe it just a coincidence, but everytime I've seen this it was with the flamemaster stuff.
 
Maybe it just a coincidence, but everytime I've seen this it was with the flamemaster stuff.

So this was my point in asking what people were using. The company "Proseal" hasn't existed for years, it was purchased by Courtaulds, then Courtaulds (former PRC) was purchased by Akzo then PPG. or at least something like that. PPG now has the products of both former companies. PS890 is the common and original "Proseal" product that meets Mil-S-8802. PR1422 and PR1440 are of the old PRC products for fuel tank sealant, but there are many others. This could be a product specific problem.

I have some work experience (more than 30 yrs) with PS890, PR1422 and PR1440 and never heard of this problem with avgas. Problems from inproper mixing and curing in an environment that was to cold, yes, but not properly mixed and cured.
 
I have some work experience (more than 30 yrs) with PS890, PR1422 and PR1440 and never heard of this problem with avgas. Problems from inproper mixing and curing in an environment that was to cold, yes, but not properly mixed and cured.

Builders here have been hearing about it for quite a while. Here's an example...note date on the photo. A Flamemaster rep has also seen this photo.

 
Builders here have been hearing about it for quite a while. Here's an example...note date on the photo. A Flamemaster rep has also seen this photo.

l'll say it a bit differently. I have not worked withthe Flamemaster product, only the PRC product. Has anyone seen this problem with the PRC product?
 
l'll say it a bit differently. I have not worked withthe Flamemaster product, only the PRC product. Has anyone seen this problem with the PRC product?

Now we are getting to an investigation, when were (date) the failed tanks made, was it pro-seal or Flame-blah at that time? How long after the units were put into service was the condition found? Was it internal or external or both? Calendar time, not flight hours.

This can begin to tell us the failure rate (or MTBF) in calendar days, etc.
 
Sealant turned to goo because the leak wasn't addressed.

Mine was a factory tank in other words a quick build kit. Be sure to check for the blue tell-tail sign of a tiny leak during annual. This will save a lot of grief next year.
 
I've been down this road with quick built tanks that did not leak but showed dozens of blisters at rivets and am not convinced anyone has hit on what is going on with the sealant going goo or blisters that do not show fuel stains or building technique applying the stuff.

What I do know, and it is not conclusive or prove anything for sure, is if you apply enough of the stuff inside the tank at ribs and covers and rivets, the tanks do not leak and the blisters do not appear - at least so far in my history with this stuff.

The RV-7A now owned by Jerry Cochran is not showing blisters to my knowledge (about 6 years,new tanks I built) and neither is the RV-8 (about 2 years). So the message is - use lots of sealant, don't be bashful about it, cover every possible place a fuel can leak out with much of it.

With any luck at all, it won't leak. And don't get all hung up with the cosmetics of how it looks. The worst cosmetic effect is seeing blue on the outside of the tank.
 
I've been down this road with quick built tanks that did not leak but showed dozens of blisters at rivets...

Off topic, so just a footnote....the blister problem was/is NOT limited to QB tanks alone. Although much blame was placed on QB's initially, collected data showed blisters were equally common in kit-built tanks.

Returning to sealant reversion....

This from a study conducted for the Navy:



The complete paper is available for download here:

http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA087267

There are some interesting clues regarding oxidation of fuels (which apparently leads to sealant reversion) in this paper:

https://web.anl.gov/PCS/acsfuel/preprint archive/Files/35_4_WASHINGTON DC_08-90_1277.pdf

100LL also has significant quantities of antioxidant added to meet the requirements of long-term storage. This list of approved antioxidants is from the UK 100LL standard; North America and AUS assumed to be similar:



I would suggest a theory ("theory" = an unproven supposition needing work to determine if it is true or false) that when 100LL gets outside the tank (like one of these fuel leaks) the antioxidant evaporates or is combined/dissolved (i.e. all used up), leaving the leaked fuel subject to a high level of peroxide formation. Acid formation may be involved/required per the paper quoted above. The acid contribution seemed to be an unknown at the time of publication (1980).

I am not a chemist, which is why I would like to see a detailed technical explanation from the sealant manufacturer. Failing that, perhaps we can crowd source a qualified individual from our ranks; we have a huge collection of intellect and education lurking on VAF.
 
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Soft ProSeal

This thread sparked my interest since I recently observed this on an aircraft that was in service for nearly 10 years. Thing is, the softening was occurring on every sealed joint on both tanks. Even those that showed no staining from leaks. If the softening is the result of the presence of oxygen and gas, well guess what, they are both constantly present. If this is the case proseal is a poor choice.

After looking at the multiple threads on this, I tend to agree with the observation that it appears to be manufacturer specific, especially in occurrences after years in service. I wonder if an informal tally of occurrences would point this out. The difficulty is many aircraft are no longer owned by the builder so identifying the product manufacturer will be difficult. Further complicated by whether or not the builder documented the source of the sealant.

I have inquired with some jet service center techs that regularly use proseal type products on fuel tanks and none have seen this. The common response was "the older it is the harder it gets". The opposite of what is occurring in these threads. Of course these shops are going to be very conscientious regarding MIL-Spec and source to meet certified standards. Experimentals are not held to that.

Maybe we all need to take stock in the old adage: you get what you pay for! There are simply some corners that should not be cut.
 
FWIW - 3M - Response

Since this came back up in another thread http://www.vansairforce.com/community/showthread.php?t=142499

I will update my (dead end) probe. I called 3M and eventually talked to a PhD in their engineering/research for the polysulfide (?) products. I sent her the pictures and thoughts from this thread about the possible cause of the color additive and the ASTM for 100LL. There were several discussions and exchanges. I followed up with her in a month (it takes a long time in large companies to fit in projects and get answers). The answer was that the even with 100LL she could not find any evidence that their product variants had exhibited "reversion". She was clearly not a marketing type and got very technical, very quickly, and seemed be genuinely interested in understanding the issue, but since there was no direct link to 3M produced material, the investigation stopped. That seemed reasonable.

If someone does use 3M and has this let me know and I can give you the contact information and get it to this engineer/scientist.

Meanwhile, my fingers are crossed for tanks.
 
To add another layer to the mystery..

Has this happened on any sloshed tanks? My tanks are over 23 years old(pro seal and sloshed) and have been fueled for about two years now, and knock on wood, no leaks. Maybe the extra layer helps.
 
Has this happened on any sloshed tanks? My tanks are over 23 years old(pro seal and sloshed) and have been fueled for about two years now, and knock on wood, no leaks. Maybe the extra layer helps.

You are going to have your own pile of problems with the slosh - just do a search on here for that subject...
 
I've read the threads on the slosh, some do and some don't have problems. If I had to do it over again, I wouldn't slosh, but I did it exactly by the book and no hints of any type of problem so far. Keeping fingers crossed on that.
 
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i am wondering what mix ratios people are using? i have been using Proseal, flame master and other types of sealants as well as a lot of epoxy resins for decades on commercial aircraft and helicopters, and have never seen sealant fail as described, unless its mix ratios are not correct, or the resin/sealant is 2 years out of date or longer.

Working with Epoxy resins, we have a general rule, of never divide by more than 1.

Usually resins come in tins of 100Grams of part A, and, for example, 22 of part B

so, divided by 1, would be 50 grams of part A and 11 Grams of part B. never smaller.

using this example, (which is Hysol 9309.3NA structural bonding adhesive) we have 100 % resin, and 22 % part B. 1 gram mistakes in measurements = 1% variation in the mix for the resin, and 5% in part B.

so, if using half, 50 resin /11 part B, then 1 gram error will = 2% but a 1 gram error in part B is nearly a 10% variation, and this will effect the quality of the final cure and its properties.

so, if you are trying to be frugal, and use 25 grams of resin, then you need 6.5 of part B, and a 1 gram error when mixing will result in a mix that doesn't cure correctly or at all. and this 1 gram error can come about by hardener (part B) that sticks to the mixing stick, or side of the container and never mixes, or unmixed resin in the corners of the container. or just scales that arnt calibrated properly, or have an accuracy variation over differing weight ranges.

Im not suggesting that this is the reason for the failed sealant described in the original post, but it is something that has to be considered when mixing sealants for critical areas such as fuel tanks, and pressurisation areas, and especially when mixing structural adhesives for composite work and bonding structural components.
 
I used 10:1 by mass, and a digital scale that displayed to .01 grams*. I'd get the hardener to within .02 grams of the target. I figured that was close enough with a claimed accuracy of .02 on the device.
 
I've mixed test samples with radically wrong ratios. They all cured, which is not a huge surprise; the manganese dioxide is a catalyst. There are minor differences in properties (shore, flexibility, tensile), but nothing radical.

The cured samples were then soaked in both a MEK/lacquer thinner mix, and in 3% hydrogen peroxide....for years. Eventually the peroxide ate the cans, but the sealant samples were intact. None reverted to goo.



This is an illustration from an Essex Chemical paper on polysulfide sealants. I have no useful knowledge of chemistry at this level, but I'm sure we have readers who do.

 
Working with Epoxy resins, we have a general rule, of never divide by more than 1.

Usually resins come in tins of 100Grams of part A, and, for example, 22 of part B

so, divided by 1, would be 50 grams of part A and 11 Grams of part B. never smaller.

Isn't that dividing by 2? Just sayin'.;)
 
GooGate Status Report

Well since this thread got resurrected I might as well give a status report regarding GooGate.

After a performing a cleaning of the area as best as I could, my fix was to lay some bigger fillets of sealant over the seams inside the first bay of the tank. I also cleaned up the goo on the outside really well and reapplied fresh sealant.

Here we are more than a year and a half later and no more leaks or goo! :)
 
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Completely anecdotal, but in the course of working at two different helicopter MRO facilities, none of the old heads would touch a can of Flamemaster sealant if it was provided with a kit, even for non-fuel sealing.
The first time someone told me not to even bother to unwrap the Flamemaster sealant that came with a medical floor kit, I figured it was just a case of "The old man's grumpy again", which was a well-known phenomenon with this particular individual. After the 3rd person at two different facilities said the same thing (almost verbatim), I figured there might be something to it.


Again, completely anecdotal. Outside A&P school, I've never worked on anything that runs on avgas, so I don't have first-hand experience with this phenomenon. I've seen sealant soften, wrinkle, and debond in integral fuel tanks (mid-'80s to mid-'90s vintage S-76 fuel tanks - whether it was the cause of the leak, or the result of the leak, is something we never attempted to determine), but never turn to goo.
 
Having not seen this thread last year when it came up, i'll just add another anecdote to the pile.

My 1996 RV-6 had the tanks opened at some point after completion, to have the anti-rotation bracket installed. Near as I can tell, all that was removed was the inboard inspection cover, with the sender and fuel pickup mounted on it. After the bracket SB was applied, the covers were re-sealed and closed. I don't have the exact date for this work, but I know it was after 1996 when it was built, and before 2010 when I bought it.

About a year and a half ago I started finding blue drips at the bottom corner of my passenger-side tank. It took a couple of months to find the source, sure enough the sealant around the cover plate had turned to goo and it was weeping around the lower half of the cover. But it wasn't doing anything more than weep a couple of drips between flights, so I left it while I figured out what to do to fix it.

Last fall I came out to the hangar one day and found a large blue stained patch under my airplane, a much larger blue stain on the belly beside the tank, and 30L of fuel missing from my tank. I drained what was left and marked that tank INOP until I could get it repaired. Last winter I took the tank off, removed the cover, cleaned everything up, and re-sealed it with new sealant from Van's.

I used the "replacing a fuel sender cover" kit, which was exactly enough for one cover, with sealant generously applied. Per Van's recommendations, no gasket was used when everything was closed up again. I re-did the seal on the fuel sender as well, as it looked like the rubber seal under it was also showing some weeping.

Of course, lucky me, I found blue stains under the other tank the last time I flew... Same problem, gooey sealant on the sender cover. So the other tank will need the same treatment this fall. Oh well. Now that i've done one tank, the other one won't take long at all.
 
Proseal failure on unused tanks

Here's another data point, with a twist, for tank Proseal that has reverted to goo.

The tanks were built about 25 years ago and have been stored empty since then (very slow build RV-6A and tanks not yet installed). I just removed the inboard access plate to complete the SB to safety the nut on the pickup tube and discovered that the Proseal on the inside of the tanks is soft paste that can be rubbed off. This includes the Proseal that is on the pre-made pickup tube screen from Vans. So there are two batches of Proseal mixed by different people, which implies the failure was NOT caused by improper mixing or a bad batch of sealant. The Proseal that is on the outside of the tanks is still all sound.

The only thing that has been in the tanks while they have been stored indoors is air, and a few litres of Avgas for initial leak testing a long time ago.

I have no idea what caused this failure but it means I now need to open up the tanks for cleaning and resealing.
 

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Anyone need two quarts of Flamemaster at a discount?

Well sh!*. I just ordered two quarts of Flamemaster from Vans to do my tanks and now rethinking whether I should use something else.
 
Sealant from Vans

Let me guess, ‘chemseal or Flamemaster’

I'm not sure what brand it was Walt and I no longer have the can but I bought it direct from Vans, in good faith, along with the pre-made fuel pickup tubes. It was shipped separately, some time after the wing kit, so that the use by date would not be expired.

I've just opened up the second tank access panel and it too is like goo inside, both the sealant in the fuel tank and on the pickup tube that was ready made.

There must be other RVs flying around in this condition. The only reason I found out about the internal state was due to opening up the tank for the SB. It seems this type of sealant is not really fit for purpose if it can fail so readily without any indication of the cause.
 
Seen it, fixed it

I have been sealing stuff for 42 years at my day job with large commercial and military aircraft. I have only used Destoto/3M/Courtalds/Products Reasearch Co.PRC , and most recently PPG products, AKA "Proseal". 1422,1440, 890,870 and the other variants produced by the above mentioned vendors,certified for the major aircraft MFG's. I currently manage KC-10 refueling tanker Depot overhaul..biggest flying fuel tank in the world, so I have seen a warehouse full of sealant in my time. Also, the entire fuselage of pressurized airliners are assembled with it, every seam, every rivet. There have been bad batches (very few), poor mixing applications (quite a few)but otherwise very few reversions related to softening not attributed to one of the mentioned causes. In my RV world, I built my -4 with Proseal (no goo in 20 years) , and repairing various other tanks, I have seen a lot of the "Goo sealant", some of which doesn't have the characteristics and identifiable color of the legacy sealants I work with. I'm not bashing any other products, I'm just stating my observations. Mixing, preparation, application and environment all contribute to the longevity and adhesion of a good sealant job, and some builders are not understanding of these factors. VANs ,VAF and the forums have really helped with the current generation of building to eliminate some of these mistakes. I'm not a chemist, and I can't say the softening is/is not caused by over/under exposure to any particular condition, I'm only speaking to a lengthy working history with the products I mentioned and the documents I must adhere to for their preparation and application in the certified aircraft world.
 
I have been sealing stuff for 42 years at my day job with large commercial and military aircraft. I have only used Destoto/3M/Courtalds/Products Reasearch Co.PRC , and most recently PPG products, AKA "Proseal". 1422,1440, 890,870 and the other variants produced by the above mentioned vendors, certified for the major aircraft MFG's. . . . . .

Bill, interesting addition of experience to the fray. I once had some projects with the 3M research center, so felt comfortable contacting them in regards to reversion. This was maybe 8 yrs ago when DanH was digging into it. I got a PhD from the lab to call me and discussed the product at length. She was so super knowledgeable and factual about the subject as to embarrass me. The buck stopped at her desk as being the top of the technical chain for responsibility for this product.

She said (summary) after having been responsible for this product in various adjusted forms, for more than a decade, she had never found any reversion of properly mixed and cured product exposed to any avgas. BUT, did say it could be something there that was a contributor as it was not tested against 100LL. She was aware of instances of reversion but they had all been traced to other causes not related to 100LL . . like mixing mostly, or contaminated product by unknown causes. She did say, use 3M, mind the instructions, and if it ever happened again to let her know. I suppose that would be all one could ask.

Her comments seems to mirror your experience as well.

Use a good brand, pay attention to the dates, and mix accurately and thoroughly.
 
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