Sealing leaking fiberglass fuel tank

I have a Avid Flyer with fiberglass fuel tanks. One of the tanks has developed a small seeping leak. Are there any products such as sealers or sloshing compounds that anyone has successfully used to seal a leak like this? What advice do you have for repairing the tank? The factory formed fiberglass tanks that came with the kit were laid up with polyester resin which isn't resistant to alcohol and although I have been careful testing for alcohol in the fuel some contamination may have occurred.
Any feed back on how to seal the leak will be appreciated.

Assuming this is just a pinhole leak and not a bigger problem, the repair on this is not that difficult. Mix up some of that polyester resin that the tank was made of. Put some negative pressure on the tank (it won't take much at all, and too much can cause more damage). You may be able to do this through your vent. Apply the resin at the source of the leak and let the negative pressure suck it in through the leak. Release the pressure, let cure and check to ensure the hole was completely filled.

I used the same vacuum procedure for sealing a leak in the end rib of my Glasair's wet wing fuel tank. Worked well but took a couple of rounds. I used a shop vac. Monitor the tank for signs of collapse while applying the vacuum...it doesnt take much. I measured the vacuum with a manaometer. Good luck!

Thanks for the suggestions. The tanks are molded to be a structural item of the wing and covered with fabric so access to the leak is limited. I'm hoping someone might have an easier solution other than removing fabric, recovering, and repainting. I will consider the clever negative pressure idea if I have to cut into the wing.

I was able to fix a pin hole leak on my COZY3 right strake tank using the slight vacuum method to suck in epoxy. Took me two trys. Finding the leak was the hard part. Put a slight presure on the tank and removed exterior and interior skin until I found the leak at the bottom of the level glass.

You can buy sloshing compounds from the usual suspects. they do take several days to dry, and are ideal if you cannot locate the source of the leak.
If you know where the leak is, then it would be quicker to cut the fabric, do a fiberglass cloth and polyester ( or epoxy.) resin repair. Double check for more leaks then repair and repaint the fabric.
Brian Evans.

Your problem is probably not due to fuel contamination. Years ago I had a similar problem with a fiberglass tank, and in the process learned that there can be a small pin hole somewhere in the interior which will allow fuel to wick along the fibers until it finds a pinhole or scratch somewhere on the exterior. I eventually ended up sloshing the enterior with commercial compound as well as painting the exterior with resin. I do like the vaccum and resin idea - especially with a thinner resin - something I should have tried! Good Luck!

Bare glass laminates can be attacked by sustained exposure to mogas with ethanol, a slower deterioration with epoxy matrix but still degrading. Best solution is to coat exposed surfaces and block direct contact with a novalac resin which is more impervious to ethanol effects. These novalcs are an epoxy/phenolic compound under the name of Jeffco 9700 or Rhino 9700. They are commercially used as coatings for concrete floors and have low viscosity so they can be sloshed or brushed on. I have the Jeffco in my Pulsar glass tanks for 7 yrs with constant exposure to 10% ethanol Calif mogas and no leaks....yet.
Bob H

Thanks Bob for the sugestions. Can Jeffco 9700 be used as a sloshing compound in a tank that has had fuel in it? I looked on the web for instructions and it appears that brushing it on is the most common usage. Any thoughts on how one would prepare the inside of tank that is installed in a wing and only accessible through the fill hole?
Todd Madison

Todd;
Yes, the Jeffco will adhere to almost any surface, and as long as it is dry, should provide good adhesion. I have used it as an interior cowl coating for oil/fuel dripping and it withstands contact; does turn slightly yellow with time/exposure.
If your tank is fixed in place, then sloshing would not work so only option is to brush coat. The smaller the opening, the harder to gain access to tank surfaces. I'd try a 1" wide brush attached to a bendable rod and try to touch all the inside surfaces with coating. Novalacs have really low viscosity and a little goes a long way for surface coverage. Mix small quantities, like 1/2 cup at a time, per mix ratio because it will exotherm in larger amounts, especially in warm weather.
For anyone with glass tanks not installed, the time to coat is now when tank can be handled and sloshed.
Bob H

Thanks to everyone for your input and suggestions. I have now have better plan to go about repairing my leak.
T Madison

When I bought a fiberglass homebuilt awhile back it had tank leaks. I tried sloshing something (red) from PolyFiber that a friend gave me and that was a large mistake. Never cured well, etc. I have no experience with the compounds that are mentioned in this thread and they may work well (fuel & alcohol resistant, adhesion, curing well), but I wound up having to remove my tank, cut it open, sand the surfaces, and coat with PolyEsther Resin. It's impervious to ethanol, bonds with epoxy resin. I have had no leaks in the 3 yrs since and am flying with mogas (Chevron). A big pointer that is mentioned in the thread is that the pinhole you find on the outside is not neccessarily where the inside hole begins. The vacuum method is not going to suck compound all the way along that path.

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Originally Posted by flyrgreen

The vacuum method is not going to suck compound all the way along that path.

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It doesn't need to. It just needs to do it enough to plug the leak. Pin hole leaks aren't very big and normally don't take much resin to seal.

Polyesters are low viscosity, cheap and are not as fuel resistant as epoxies. Many tanks for kitplanes are made from it because of cost and you can identify polyesters by sanding a tiny corner and smelling for styrene. Epoxies would have no styrene odor.
The novolac (epoxy/phenolic) is lower viscosity and more fuel resistant, so it would be a better choice. If your tank is sealed and working, just keep the material choices in mind for next resealing.

In my previous reply I mis-identified the compound I used to repair my fiberglass tank. I in fact used Vinyl Ester Resin, from reading in one of the EAA publications, that recommended Vinyl Ester for it's resistance to ethanol (and alcohol in general). I'm hoping to hear from some of you that this was the right move. -rg-

If you used a vinyl ester resin to repair a structural issue in tank and left it bare, it will eventually breakdown in ethanol mogas over several years. It also depends on the concentration of the ethanol. In Calif, it's 10% ethanol. If you used the vinyl ester and coated it with novolac to keep ethanol from contacting the ester, tank will last much longer. So it depends on how ester was appiied and it's exposure. If you can still coat tank interior, no matter what the structural resin system, it wold be beneficial to avoid breakdown over time.

If you put a tank into service and monitor the fuel filter, gradual breakdown will produce a fine sludge and then small bits of glass fibers. By the time fibers are showing, the breakdown is progressing. Coating at that point may keep damage from accelerating and save tank. I feel it's better to coat first and avoid any breakdown.

Often on threads like this, people come from different situations so it's hard to give an overall answer to every question. Some will swear that bare structure of any resin will withstand mogas exposure, only to find that their mogas has no ethanol or a very low concentration so they really have no dissolution issues. Others with high concentrations will eventually have a problem. My recommendations are based on a high ethanol (10%) continuous exposure.

Re the last post: This is simply not true... Vinylester IS impervious to fuel and needs noadditional coating. How do I know this? I own a Glasair III that is constructed using Vinylester resin (yes, even the fuel tanks) and there is no need to coat the tanks with anything. Hundreds of Glasairs have been flying for the last 25+ years without a problem.

The problem concerned mogas with ethanol. If you are using avgas without ethanol, no problem, as almost all of the tank resin systems will work. But if you are using mogas, there will be gradual degradation without a coating.

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Originally Posted by Brian E. Evans

You can buy sloshing compounds from the usual suspects. they do take several days to dry, and are ideal if you cannot locate the source of the leak.
If you know where the leak is, then it would be quicker to cut the fabric, do a fiberglass cloth and polyester ( or epoxy.) resin repair. Double check for more leaks then repair and repaint the fabric.
Brian Evans.

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A P-51 Test pilot with over 13,000 hours died in Florida on his second flight in a Stewart P-51 and this was due to the lack of integrity of all sloshing compound sealants. I do not recommend ANYONE using this product for ANY application whatsoever. It will desegregate and clog causing fuel starvation.

Sincerely and Respectfully,

Yellowhammer

Quote:

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Originally Posted by Yellowhammer

A P-51 Test pilot with over 13,000 hours died in Florida on his second flight in a Stewart P-51 and this was due to the lack of integrity of all sloshing compound sealants. I do not recommend ANYONE using this product for ANY application whatsoever. It will desegregate and clog causing fuel starvation.

Sincerely and Respectfully,

Yellowhammer

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Can you provide some specifics on the cause of that fatal crash?

Thanks,


BJC

I posted some info to this thread in 2011 and didn't revisit until now. I wrote that normal Epoxy Resin will break down from exposure to Ethanol in Mogas, but EAA and others say Vinyl Esther Resin will not. I see that Bob H. has made a comment that this is not true. Bob, if you're still here, please provide your source for saying VE Resin cannot withstand ethanol. You are saying that EAA's info is incorrect.
As for the recent questions here about sloshing compounds-- there are many and I doubt one can lump them all in together. Some may be tolerant to Ethanol.... But another issue is actual sloshing & coating process. That's dicey. Since you can't see inside the tank as you work the slosh, you don't know if you have gotten that stuff in the fuel exit hole, or the vent hole. Or on the fuel level sensor apparatus, if you weren't able to take it out. The guys who owned my KR-2 before me tried this and failed. Compound was in both the areas I mention. I had to cut the tank open and completely resurface the whole thing.

Here is an example of epic sloshing failAttachment 7794

Most polymer laminating systems will eventually breakdown in presence of ethanol and that includes both epoxies and vinyl esters. The resistance to breakdown is in the degree of crosslinking of the resin; higher linking, higher resistance. Most epoxies get the higher linking by heat curing. A 350F curing epoxy will have high linking and will withstand solvents like ethanol. A room temp epoxy has lower cross linking density and will be suseptible to eventual breakdown.
Polysulphide sealants are formulated to resist breakdown and make good fuel/ethanol seals.
The Rhino 9700 novalac is a coating with great chemical breakdown resistance, however it is brittle and can develop cracks over time, especially if the tank sees any flexing. I have used the 9700 as a protective barrier for the RT cure epoxy but it eventually cracks and that allows ethanol fuel to come in contact with laminating epoxy. I did find a flexible polysulphide from Spruce ( $38/qt kit) that is brushable and now use it whenever I want to seal tank joints that might flex. Has worked well for 2+ yrs on Pulsar integral glass tanks.

Any sort of bond depends on the surface ability to bond. I would think a fuel tank in service is a poor surface to expect bonding. Fuel might contain oils.
Usually, a good bond requires sanding away or chemical removal of the surface before bond. If the surface had oil or silicone a proper slosh bond may be impossible.

At the risk of derailing things, I've always wondered why they haven't come up with a bladder to insert in spaces like that, much like the stuff they make fuel blivets for the Army out of, but thinner.

Cessna 180’s do have rubber fabric bladders stuffed in the wings. They have problems with age.

Bob H-- Your comments seem well-grounded in knowledge and experience. I'm sure the tech counselors at EAA who have promoted Vinyl Esther resin as being ethanol resistant would like to have a discussion with you. Seriously, this is critical info that they have apparently gotten wrong and need to correct.

Bill Berson-- You are absolutely correct about surface prep before applying any resin. I talked to pro fiberglass people about applying to "in service" glass; they said an acetone wash at the very least, sanding if possible.

In the bonding business, surface preparation is the most important factor for good adherence. For non-metallic surfaces like epoxy laminates, you would like both mechanical abrasion and chemical activation for the adhesive or coating to bond to. Sanding provides the mechanical "tooth" and solvent wiping just prior to application of adhesive provides chemical activation. This gives a good combination for a strong bonding surface. Actually, a light grit blast is even better.

On metals, the chemical activation is absent as most metals are not reactive to normal solvents. A variety of metal surface activation processes were developed in the aerospace business like Phosphoric Acid Anodizing (PAA) or FPL etching followed by a heat cured primer. This gives a strong surface for adhesion on aluminum and provides corrosion resistance.
But for a metal tank that's not open for accessibility, these techniques won't work. A metal tank that can be grit blasted and cleaned would give a good bonding surface.
If you just throw a solution into a tank and slosh it around, you may not get strong adherence to the metal, and the coating could eventually separate and cause more problems.
So for a tank made of organic materials (epoxies, vinyl esters, etc), you want to mechanically abrade and chemically wipe at the time of coating application.

When folks have discussions about dissolution effects of ethanol on tank materials, there are many variables in play like concentration of the ethanol, tank material, temp of operation, time of exposure, and more. Most chemical testing is done on ethanol exposure measured in weeks or months. Yet most aircraft tanks hold ethanol fuel for years. Someone may say that a particular tank material is impervious to ethanol exposure, but you need to make sure the tank material is seeing very long-term exposure before giving it a blessing. My technical opinion is that most homebuilt structural laminating resin systems will be susceptible to ethanol exposure if the surface is left bare and you need a coating to keep the ethanol from the resin to maintain laminate integrity.

Sorry for the long answer.

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Originally Posted by Bob H

Most polymer laminating systems will eventually breakdown in presence of ethanol and that includes both epoxies and vinyl esters. The resistance to breakdown is in the degree of crosslinking of the resin; higher linking, higher resistance. Most epoxies get the higher linking by heat curing. A 350F curing epoxy will have high linking and will withstand solvents like ethanol. A room temp epoxy has lower cross linking density and will be suseptible to eventual breakdown.
Polysulphide sealants are formulated to resist breakdown and make good fuel/ethanol seals.
The Rhino 9700 novalac is a coating with great chemical breakdown resistance, however it is brittle and can develop cracks over time, especially if the tank sees any flexing. I have used the 9700 as a protective barrier for the RT cure epoxy but it eventually cracks and that allows ethanol fuel to come in contact with laminating epoxy. I did find a flexible polysulphide from Spruce ( $38/qt kit) that is brushable and now use it whenever I want to seal tank joints that might flex. Has worked well for 2+ yrs on Pulsar integral glass tanks.

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Are you refering to the Bill Hirsch automotive gas tank sealer ( p/n 09-03477)? The description did not mention polysulphide.

Does anyone else have experience with this product?

Wayne

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Originally Posted by Eckertwa

Are you refering to the Bill Hirsch automotive gas tank sealer ( p/n 09-03477)? The description did not mention polysulphide.

Does anyone else have experience with this product?

Wayne

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I sloshed the Epoxy resin glass tanks in one of my planes when I was building it using the Bill Hirsch Alcohol resistant sealer. The tanks have been in service for 22 years now, and well over 1200 flight hours with no hint of delamination or peeling. I did slosh them when they were new, so had never had any oils or petroleum products in the tanks. Sloshing tanks requires proper prep for proper adhesion, just like painting.