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  #1  
Old 08-08-2018, 06:12 PM
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Default Flamemaster Tank Sealant Questions

Hi All,

I started my fuel tank sealing last weekend, beginning with the skin stiffeners. I decided to go with the method laid out by Rick Galati in the "sticky" thread. so far the sealing at least has gone well, but I have a question and a caution.

First, the caution, which is not really directly related to the fay sealing method, but more to methods of masking. I chose to mask areas around the stiffeners so that I could avoid getting a mess of sealant on the skin. Turns out I needn't have worried much, and caused myself more problems overall by doing the masking.

My main bad decision was using "scotch tape" (actually Staples brand "invisible tape", P/N 34-8711-4390-3) to mask. Most of the experiences I've had with this kind of tape made me think it really didn't stick much.

What I failed to consider was that when you prepare an aluminum surface to maximize adhesion, the tape will stick far better than you ever imagined that this kind of tape can stick. It becomes a film that is only fully removable with lots of physical effort and solvent.

Which brings me to the question: how tenacious should this sealant be? I am using the Flamemaster CS-3204 B-2 provided by Van's. Tech sheet here: http://flamemaster.com/wp-content/up...rev-09-131.pdf

The tech sheet says "For surface preparation as well as removing fresh or cured CS 3204, Methylene Chloride can be used. Cured CS 3204 will
require a soaking period in Methylene Chloride bases stripper for satisfactory removal. "

I have been using MEK, acetone, and ethanol to remove the "scotch" tape residue. MEK seems to work the best, followed by acetone, with ethanol being a very distant third, almost useless in getting the tape off, but it does a decent job on the underlying tape adhesive. Note that I have been doing a very good job of keeping the solvents away from the sealant!

I was nervous about getting MEK and acetone too close to the sealant itself, because of other things I have read that say MEK can be used to remove the sealant.

However, everything I have read indicates that the sealant should be extremely difficult to remove. I understand that until the sealant reaches full cure, it will be easier to remove, but even without solvent, I find I can remove it from the aluminum surfaces pretty easily just by getting my fingernail around the edge and then pulling on it.

Should I be able to do this at all? I set this sealant on Sunday afternoon, struck rivets on Monday evening, and now on Wednesday, I can still peel back the sealant fairly easily.

The aluminum was prepped by acid etching and alodining several weeks ago, and then cleaning with MEK, drying, scuffing with maroon Scotch Brite, and then cleaning again with MEK, and drying prior to sealant application. I can't think of anything more I could have done to prep the surface better.

The sealant has an expiration date of 09/18, but I have kept it in the freezer since I received it in April. I warm it up to room temp (mid 70s fahrenheit) thoroughly before mixing and using. The mix is definitely correct (used 5g B : 50g A)

The sealant seems to have a solid hold until I mess around with it with my fingers. Is this normal?
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Old 08-08-2018, 06:31 PM
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Default

One happy coincidence here is that at least 100LL appears to dissolve scotch tape pretty well, and presumably it doesn't do much to the tank sealant.
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Old 08-08-2018, 07:27 PM
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RVbySDI RVbySDI is offline
 
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Default

"Is there anything else I can do?"

Well, MEK does leave a residue so one other thing you might do is go buy some cheese cloth and wipe down all surfaces that had MEK.

As for getting proseal on the skins, don't even worry about having extra on things. It is not going to make any difference. Slop it in and cover EVERY seam and EVERY hole with lots of proseal.

Ask me how I know, but you don't want to have a leak when you are finished. Sealing the fuel tanks is not a beauty contest. Don't skimp on proseal and just get it sealed and move on.
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Last edited by RVbySDI : 08-08-2018 at 09:28 PM.
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Old 08-08-2018, 07:35 PM
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Quote:
Originally Posted by RVbySDI View Post
"Is there anything I else you can do?"

Well, MEK does leave a residue so one other thing you might do is go buy some cheese cloth and wipe down all surfaces that had MEK.

As for getting proseal on the skins, don't even worry about having extra on things. It is not going to make any difference. Slop it in and cover EVERY seam and EVERY hole with lots of proseal.

Ask me how I know, but you don't want to have a leak when you are finished. Sealing the fuel tanks is not a beauty contest. Don't skimp on proseal and just get it sealed and move on.
What residue does MEK leave?

I mean, other than whatever was dissolved in it when it evaporates? Which should have been nothing, since I washed and wiped it multiple times.

Last edited by 1001001 : 08-08-2018 at 07:45 PM.
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Old 08-08-2018, 08:51 PM
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Default MEK

I'm no chemist but I think the issue is the MEK does something to the sealant or the bond. Many have had leak issues due to using MEK as a cleaner. Use a less volatile solvent to clean up the tape or any other areas.
Keep a sample of the sealant and date it. It makes a good control. You can compare to the control sample. Often mix rate and temp can effect the set time.
I only used MEK to clean the areas before sealant. Nasty stuff. Use a good respirator.
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Old 08-08-2018, 09:09 PM
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Quote:
Originally Posted by wirejock View Post
I'm no chemist but I think the issue is the MEK does something to the sealant or the bond. Many have had leak issues due to using MEK as a cleaner. Use a less volatile solvent to clean up the tape or any other areas.
Keep a sample of the sealant and date it. It makes a good control. You can compare to the control sample. Often mix rate and temp can effect the set time.
I only used MEK to clean the areas before sealant. Nasty stuff. Use a good respirator.
Yeah, I have found that ethanol works OK for dissolving the tape if left to sit long enough. 100 LL works well to clean up the residual adhesive (from the tape).

MEK is pretty low on the totem pole of toxic chemicals I come in contact with regularly in my work. I of course use protection but it's not that much to worry about in the grand scheme of things.

I agree MEK might thin the sealant (it is not recommended as a sealant thinner for other reasons, but has that effect). I'm not sure it does much to the bond unless it is worked under the bond physically.

Anyway, I think EtOH and 100LL are the way to handle this problem now.

Thanks!
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Old 08-09-2018, 06:49 PM
Tommy123 Tommy123 is offline
 
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Default MEK

I spent decades doing fuel tanks and pressurized skin repairs on Boeing and Douglas aircraft. MEK is the only efffective way to clean up fuel tank sealant. The sealant laughs at alcohol. MEK will not dissolve cured sealant with incidental contact, if applying new over old sealant it will help the bond if you wipe down and dry with MEK. It will not leave a residue but wipe the area dry, don’t let pools evaporate.
MEK has been effectively been banned in the commercial world and replaced by MPK which is nowhere as effective. Lowe’s still carries MEK.
Yes MEK is nasty stuff that causes cancer use your brain when dealing with it.
If you need thinner sealant use type A rather than type B.

Last edited by Tommy123 : 08-09-2018 at 06:57 PM.
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Old 08-10-2018, 04:53 AM
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Quote:
Originally Posted by Tommy123 View Post
...
MEK has been effectively been banned in the commercial world and replaced by MPK which is nowhere as effective...
Yes MEK is nasty stuff that causes cancer use your brain when dealing with it.

Thanks for your reply! I have to note however, that your assertion that MEK causes cancer is unsupported by evidence. It is not listed by any agency that I could find as a carcinogen. Even California's Office of Environmental Health Hazard Assessment does not list is as a carcinigen.

I have not found any evidence that MEK (more properly known as butanone) is the subject of any general bans in commerce. Yes, it requires the use of appropriate PPE as it has some health effects, but causing cancer is not one that has been supported by evidence.

I don't wish to be harsh here, but it pays us to be aware of facts and not fearmongering. I don't accuse you of it, but there is lots of unfounded fear about "chemicals" out there, and plenty of people who don't care to know the facts--only to sow fear and discontent. As a chemical professional, I have unfortunately been seeing this my whole career and try to fight it when I can.
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Old 08-10-2018, 06:47 AM
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Quote:
Originally Posted by wirejock View Post
I'm no chemist but I think the issue is the MEK does something to the sealant or the bond. Many have had leak issues due to using MEK as a cleaner.
MEK use was not a common factor in fuel tank paint blisters. I very much doubt MEK on a cleanup rag is a factor in leaks.
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Old 08-10-2018, 08:28 AM
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Default Retraction

I stand corrected. Need to book a few nights in Holiday Inn.
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Donated 12/01/2017. Plus a little extra.
RV-7A #73391, N511RV reserved (1,800+ hours)
HS SB, empennage, tanks, wings, fuse, working finishing kit
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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