Tank seal... Issues afterwards

[FlyingDude]

Hi guys,

I fixed a leaking tank successfully in June. It stopped leaking. I could fill it up and come back a few days later to a clean underbelly... But now, 4 months later, it started leaking from the same spots. What went wrong?

1) was the surface prep not good? I had cleaned all previous sealant and wiped the surface with alcohol profusely.

2) were the 2 parts not mixed properly? Though I did count to 60 (not 50 as in the instructions) while mixing it.

3) what else could have gone wrong?

Also: when you buy the quart size that comes in cans (not the syringe) what equipment do you use to mix it? 

Please give PIREPS based on your experience. 

Thanks.

[Browncbr1]

Go over it again with the red honey top coat again.   It takes a few tries sometimes.  

[FlyingDude]

38 minutes ago, Browncbr1 said:

Go over it again with the red honey top coat again.   It takes a few tries sometimes.  

Is that the cs3600? I don't get it: how will applying top coat fix today's leaks? Isn't it too late? A channel has already opened through the cs3204. How will too coat fix that? By seeping into the cracks?

Thanks.

[Shadrach]

On 10/10/2021 at 8:17 PM, FlyingDude said:

Is that the cs3600? I don't get it: how will applying top coat fix today's leaks? Isn't it too late? A channel has already opened through the cs3204. How will too coat fix that? By seeping into the cracks?

Thanks.

A leak on the inside near your old repair could manifest itself externally in the exact place where the previous leak showed.  Methyl Ethyl Ketone (MEK) is superior to denatured alcohol for surface prep. MEK will temporarily soften the the surface of existing sealant helping a new repair to adhere. Lint free microfiber should be use, not cotton. 
Was the soapy water vacuum test used to find the first leak? I agree with comments above that you should use a generous coat of PR1005 after laying down the CS3204. Disagree that you should try to repair a leak with just PR1005.

 

[FlyingDude]

Thanks for the responses and info.

So, I didn't actually patch the leaks. I stripped those edges completely and resealed the 2 sides of the stringer and top and bottom edges of the inboard wall. So any issue with adherence was between bare aluminum and cs3204. After I removed the old sealant, I cleaned the surfaces with isopropyl alcohol. Was that bad? Should I have used MEK on the bare aluminum? Why didn't it stick?

Thank you.

 

 

 

[Shadrach]

3 minutes ago, FlyingDude said:

Thanks for the responses and info.

So, I didn't actually patch the leaks. I stripped those edges completely and resealed the 2 sides of the stringer and top and bottom edges of the inboard wall. So any issue with adherence was between bare aluminum and cs3204. After I removed the old sealant, I cleaned the surfaces with isopropyl alcohol. Was that bad? Should I have used MEK on the bare aluminum? Why didn't it stick?

Thank you.

 

 

 

What did you strip it with? Di you flush the tank thoroughly with water before prep?
You don’t know that it didn’t stick. you will need to Do the soapy water trick to see where it’s actually leaking.

[N201MKTurbo]

8 minutes ago, FlyingDude said:

Thanks for the responses and info.

So, I didn't actually patch the leaks. I stripped those edges completely and resealed the 2 sides of the stringer and top and bottom edges of the inboard wall. So any issue with adherence was between bare aluminum and cs3204. After I removed the old sealant, I cleaned the surfaces with isopropyl alcohol. Was that bad? Should I have used MEK on the bare aluminum? Why didn't it stick?

Thank you.

 

 

 

Thank you!

I hate the word “patch”. There is no approved procedure for patching a tank. 
 

The repair procedure is in the maintenance manual. 
 

Don’t feel bad, I’ve had to go into a tank a few times before it gets all the issues. Most likely, your repair was good and whatever caused the original leak manifested itself somewhere else. Maybe if you just went one more inch in that direction, you would have got it.

The repairs are usually minor work compared to the access panels.

[FlyingDude]

5 minutes ago, Shadrach said:

What did you strip it with?

Acetone and muscle power.

I didn't flush it because I didn't use polygone. Acetone just evaporates, right? You think it left some residue?

I didn't do the soap test but I redid the entire side and it stopped all leaks. For 3 months, I could keep the tank full. Now it's leaking from the same side again (inboard wall). Maybe it's not leaking from the exact same spot as before but it's leaking from the freshly sealed wall. So, my reseal job has failed. 

[Shadrach]

6 minutes ago, FlyingDude said:

Acetone and muscle power.

I didn't flush it because I didn't use polygone. Acetone just evaporates, right? You think it left some residue?

I didn't do the soap test but I redid the entire side and it stopped all leaks. For 3 months, I could keep the tank full. Now it's leaking from the same side again (inboard wall). Maybe it's not leaking from the exact same spot as before but it's leaking from the freshly sealed wall. So, my reseal job has failed. 

Acetone and alcohol should have been sufficient to prep. Did you finish with PR1005?  Do the soap test and report back. It should be an easy touch up.

[FlyingDude]

3 minutes ago, N201MKTurbo said:

Don’t feel bad

Thanks mate

So far I've spent $200 on materials. The hours will count towards my AP apprenticeship. I'm not feeling too bad. I just want to figure out what I did wrong and then do it right this time. Winter is coming so I need to get it done while the compound can still cure

Could you answer my following questions:

1) how do you prep bare aluminum for best adhesion?

2) what equipment do you use to mix the quart size cs3204 that comes in cans and not syringes?

3) how do you tell that the compound has been mixed well enough apart from counting the twists? 

4) given the tight spaces and lack of top access panels, I applied the compound with putty spreaders. What would you have used?

thank you very much.

 

[FlyingDude]

3 minutes ago, Shadrach said:

Did you finish with PR1005?  

No. 

At this point, I'm thinking if I should just blast those edges/walls with polygone and start over. I can do the soap test and do a spot repair but as you said, the access panels are the longest part of the process, so I'd rather redo those edges than to enter the tank 3-4 times...

[MB65E]

MEK will leave a residue. 
denatured alcohol will not.
Everyone swears by MEK but I’ve used it less and less over the years.  But I   Agree on the softening properties of MEK. 
-Matt
 

[N201MKTurbo]

I mix it in Dixie cups with popsicle sticks. I thin it a bit with MEK and apply it with a 1 inch chip brush. I throw away both after use. If you get the 1/4 inch stir sticks for the black stuff and. 3/4 inch stick for the pink or grey stuff and get a similar dollop on both, it is a good mixture. 
 

Prep the surface as the manual says. Clean it with a fresh cloth with MEK until the cloth comes out clean.

Edited October 11, 2021 by N201MKTurbo

[FlyingDude]

Thank you for your help. I'll let you know how it goes...

[FlyingDude]

One more question: how much polygone is used for one tank? Thanks

[carusoam]

Follow the instructions as closely as you can…

make no substitutes for cleaning and prep materials…

Alcohol has an unwanted ability to bring moisture with it….

 

When it comes to mixing viscous materials… squeeze and thin, squeeze and thin, repeat, a lot…

You can’t over mix it, but it is easy to under mix….

Don’t be in a rush to toss out your unused mixed samples…. You will know exactly how well things are mixed the following day… if they are still tacky, days later… you have a problem… could be mixing, could be age of materials, could be a freshness issue caused by a leaky package…

 

Some two part epoxies use two colors to help visualize the quality of mixing…

When it comes to mixing polymeric materials… you are trying to get molecules of one material to intermix with the other as closely as possible…

 

Mixing on a flat surface is like spreading peanut butter, recollect, and spread again….  About 1k times will work really well… 

Its like stretching and folding dough… doing it 1k times, one layer is automatically 1/kndths of the original thickness….

It sounds like a lot of stirring, but it is really hard to get anywhere near the molecular level…

 

keep folding everything in… or the percentages don’t work out as planned… if you leave edges of the surface not blended into the mix…

 

Two types of mixing and mass transfer are occurring…. Turbulent and laminar… stirring is one kind, knife spreading is the other…

Stirring helps bring one side of the container to the other…good for bulk mixing… spreading brings one layer of molecules in contact with the others… very localized mixing…

If you approached this like stirring water based paint… that’s probably not enough stirring…  similarly, the final painting of a thin layer is often the final mixing step…

Oddly there are dual syringes with attached mixing heads… that do a pretty good job of the first stirring step…  wouldn’t want to rely on that to work on a project that should last 20+ years…

Don’t be afraid to over mix, unless you are running out of time or temperature or daylight… or some other limitation…

PP thoughts only, not a polymer chemist… I may have mixed some viscous materials at work…

Best regards,

-a-

 

 

[N201MKTurbo]

57 minutes ago, carusoam said:

Don’t be in a rush to toss out your unused mixed samples…. You will know exactly how well things are mixed the following day… if they are still tacky, days later… you have a problem… could be mixing, could be age of materials, could be a freshness issue caused by a leaky package…

I always set the Dixie cup, brush and stir sticks aside. You can check them the next day to see how they set up.

[N201MKTurbo]

1 hour ago, FlyingDude said:

One more question: how much polygone is used for one tank? Thanks

I’ve never used Polygone, I just scrape with a plastic scraper and clean up with MEK. I would worry about polygone affecting the existing sealant during a repair.

[JWJR]

How long did you give it to cure prior to adding fuel again? The longer the better. 7 days at reasonable temps and humidity or longer is best.

I would start over and do the soap test first. You want to see the EXACT spot inside the tank. Use plenty of soap and blue painters tape to secure the plexiglass and remove the tape and move the mirror around a few times and re-tape the plexiglass to find the bubbles.The leak (bubbles)you see below was not the same place as the fuel stain and dripped under the wing.

The sealants used today adhere very well to most anything so perhaps you missed the spot.

Please do follow up and let’s us know what you find when you go back in the tank. Good luck




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[N201MKTurbo]

Blue painters tape? That’s crazy talk! Duct tape is the stuff!

I bet you take off without flaps, fly LOP and do touch and gos.

[Shadrach]

1 hour ago, N201MKTurbo said:

I’ve never used Polygone, I just scrape with a plastic scraper and clean up with MEK. I would worry about polygone affecting the existing sealant during a repair.

This is a concern. The work around is to manually remove the borders of the area to be repaired. Then apply the polygone to the area inside or below. I recently did the bottom of the inner, rear left fuel cell. I used polygone but removed the 1/2 inch above the filet manually. It came out nice. Cleaning the area around the sump without having polygone would have been tedious. In truth, It was pretty tedious with polygone.

 

 

 

 

Edited October 11, 2021 by Shadrach

[N201MKTurbo]

If it isn’t tedious, you are doing it wrong.

Its a sucky job.

[JWJR]

Blue painters tape ( yes lots of it) comes off easy so you can pull the plexiglass and move the mirror a few times. Lol no touch an goes
As I like to keep the gear cycles to a minimum.
I forgot to mention that a pump sprayer filled with water is great for flushing the tank with water to remove the soap.


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[JWJR]

https://web.archive.org/web/20200220152111/http://donmaxwell.com/fuel-tank-repairs-how-we-fix-them/


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[FlyingDude]

Thanks for all your info.

1) Don Maxwell page refers to cs-3600 for top coating, not pr-1005. How come? I saw that 3600 is a glue!!

2) I did build plexiglass windows. I laid down window sealing ribbon bands following the outline of access panels to achieve seal. Used thin plexiglass, so that it breaks before vacuum reaches any level that could implode the tank. Though I don't know if I can use the soap method with extended tanks because I only have access from the bottom. Do the soap bubbles persist after vacuum is gone, so I can look for them AFTER removing vacuum and plexiglass windows? You think I could use a dye? Maybe water soluble ink?

3) I used B1/2 as it takes me 11 minutes to go through one syringe. Yes I set a timer that beeps every 10 min. Waited 40 hrs in June, 33% longer than in the instructions. Hot and humid, as Michigan gets. Then cleaned it with alcohol and then sealed the access panels and waited another 14hrs for the cs3330b1/2 rather than the 10hrs per instructions... So in total ~60hrs before adding fuel. You think that was too soon??? 

4) I might get the gel version of polygone and apply it on edges that butt against other edges to be removed, to prevent damaging edges that are to remain. 

5) so should I do the final clean up with Mek or alcohol? I read mek releases residues but it softens the CS, whereas alcohol is hydrophilic and introduces water but cleans up residues. Which one is it?

6) I miss flying... My repair/fly ratio has exceeded 10:1 and I'm not really happy about it.

Thanks guys.