Overcoating sealer outside the tank

170 driver · #1 10-18-2017, 01:31 PM

I was wondering if anyone has found anything that can be used to overcoat the exposed sealer on the outside and rear of the tank to prevent the blue dye from a small leak from softening the sealer in a big area and causing massive rework? It seems that there should be some coating that is impervious to the blue dye. This could make small leaks an easier repair.

170 driver · #2 10-19-2017, 07:06 AM

It's not the 100LL that softens it, otherwise the sealer would be soft inside the tank. It is only when the fuel evaporates and leaves the blue dye on the sealer that it becomes soft. It must have an effect on the hardener that is in the sealer. If you have an rv, you will eventually see this I'm about sure. I don't think it is possible to construct a completely leakproof tank, my right tank held for 9 years till a sending unit screw just started seeping onto the sealer and softened it. The left tank only lasted 2 years before I had to repair it.

Snowflake · #3 10-19-2017, 07:28 AM

I'll go one step further - It's probably neither the fuel nor the blue dye. If the sealer is softening, it's more likely that it wasn't fully mixed, or wasn't mixed in the right proportions.

erich weaver · #4 10-19-2017, 08:10 AM

Quote:

Originally Posted by Snowflake

I'll go one step further - It's probably neither the fuel nor the blue dye. If the sealer is softening, it's more likely that it wasn't fully mixed, or wasn't mixed in the right proportions.

What he said.

E

rvbuilder2002 · #5 10-19-2017, 08:30 AM

Quote:

Originally Posted by Snowflake

I'll go one step further - It's probably neither the fuel nor the blue dye. If the sealer is softening, it's more likely that it wasn't fully mixed, or wasn't mixed in the right proportions.

Quote:

Originally Posted by erich weaver

What he said.

E

Search the archives here in the forums... there is a lot of past discussion.
One in particular..... My cured Pro-Seal has turned to goo!
http://www.vansairforce.com/communit...light=pro-seal

It will indeed happen with sealant that was properly ratio'ed and mixed.

How do I know?
I have seen it happen on sealant that had been (thoroughly) mixed from one of the small pre-portioned kits (besides numerous other times).

To answer the original question - If all of the softened sealant can be removed and the surface well cleaned, fresh sealant will adhere very well to old/cured sealant. This will sometimes resolve a leak depending on what the leak source is.

RVbySDI · #6 10-19-2017, 08:49 AM

To borrow from Hans and Franz: "Hear me now and believe me later!"

The only way to accomplish what you are trying to figure out is to figure out a different way to build an RV fuel tank. Be assured there is only ONE way to stop the blue dye (fuel) from showing up on the outside of a fuel tank seam. Find the leak, open the tank up and reapply the proseal from the inside of the tank. No amount of attempting to seal from the outside will affect the leak.

Ok, go ahead. Ask me how I know!

rvbuilder2002 · #7 10-19-2017, 09:20 AM

Quote:

Originally Posted by RVbySDI

To borrow from Hans and Franz: "Hear me now and believe me later!"

The only way to accomplish what you are trying to figure out is to figure out a different way to build an RV fuel tank. Be assured there is only ONE way to stop the blue dye (fuel) from showing up on the outside of a fuel tank seam. Find the leak, open the tank up and reapply the proseal from the inside of the tank. No amount of attempting to seal from the outside will affect the leak.

Ok, go ahead. Ask me how I know!

I agree that you are correct for the majority of leak instances but tiny leaks do occasionally get repaired by sealing from the outside which is why I wrote "depending on what the leak source is".

RVbySDI · #8 10-19-2017, 09:47 AM

Quote:

Originally Posted by rvbuilder2002

I agree that you are correct for the majority of leak instances but tiny leaks do occasionally get repaired by sealing from the outside which is why I wrote "depending on what the leak source is".

I speak from my personal experience (7 of them actually). I did have experience with very very small pinhole leaks. In multiple attempts to seal those small pinhole leaks from the outside not one of the attempts worked for more than a couple of months before they started leaking again. I am now coming up on 4 years of leak free flying after drilling out 5 four inch diameter holes in each bay of my left fuel tank, resealing with proseal all seams on the inside of the tank, and sealing up the holes with the Vans Fuel Tank Repair Kit (5 of them).

It is somewhat concerning to think about removing a fuel tank, opening it up, and especially drilling a great number of new holes into the tank (including one great big hole). Given that, I will say with confident assurance, doing so does work.

170 driver · #9 10-19-2017, 11:34 AM

I can say with certainty that the Proseal 890 sealer was properly mixed and in the correct ratio as weighed on a digital scale and well within expiration date. Only the areas with blue stains are soft and the rear baffle was sealed with all the same mixed batch. My left tank has the 4 holes cut in it with the Van's repair kits, it continues to hold after a year. It just seems unnecessary for a 1 foot section of the rear baffle lower seam and the inboard lower rib to all be soft and have to be repaired due to a tiny leak at one fuel sender screw. I know if I don't repair it properly from the inside it will eventually leak in those areas due to soft sealer. I have talked to a knowledgeable guy on polysulfide sealer and epoxy coatings and he said the chemical that is breaking down the sealer is breaking it down at a molecular level and not just deactivating the hardener in the sealer. I will brush on two part epoxy Scotchweld DP460 on all the exposed sealer outside the tank, he says hardened epoxy is the most chemical resistant coating he can think of. It can't hurt. Fuel leaks are the pits.

erich weaver · #10 10-19-2017, 04:45 PM

Quote:

Originally Posted by rvbuilder2002

Search the archives here in the forums... there is a lot of past discussion.
One in particular..... My cured Pro-Seal has turned to goo!
http://www.vansairforce.com/communit...light=pro-seal

It will indeed happen with sealant that was properly ratio'ed and mixed.

How do I know?
I have seen it happen on sealant that had been (thoroughly) mixed from one of the small pre-portioned kits (besides numerous other times).

Huh. Do you have any explanation for what exactly causes this, or a solution for stopping it from occurring? Its a little disturbing to think that the very substance recommended by Vans to seal tanks is, in at least some cases, turned to goo by ingredients in aviation fuel.

erich