My cured Pro-Seal has turned to goo!

[ArVeeNiner]

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?

[fixnflyguy]

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.

[9GT]

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.

[rvbuilder2002]

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.

[alpinelakespilot2000]

Originally Posted by rvbuilder2002

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?

[David Paule]

Does this imply that the tanks must be full after every flight?

Dave

[aturner]

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[gmpaul]

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.

[rvbuilder2002]

Originally Posted by alpinelakespilot2000

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.

[BillL]

Originally Posted by rvbuilder2002

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?